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[PATCH v1 3/3] Allow building only trusted or untrusted PL/Tcl.
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* [PATCH v1 3/3] Allow building only trusted or untrusted PL/Tcl.
@ 2022-05-18 21:33 Nathan Bossart <nathandbossart@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Nathan Bossart @ 2022-05-18 21:33 UTC (permalink / raw)

Presently, when the --with-tcl configuration option is used, both
trusted and untrusted PL/Tcl are built.  However, some users may
only want to build one or the other.  This change introduces an
optional argument that can be used to do so.  If
--with-tcl='trusted' is specified, only trusted PL/Tcl is built.
If --with-tcl='untrusted' is specified, only untrusted PL/Tcl is
built.  If --with-tcl is given without an argument, both trusted
and untrusted PL/Tcl are built.
---
 configure                      | 47 +++++++++++++++++++++++++++++++---
 configure.ac                   | 32 ++++++++++++++++++++++-
 doc/src/sgml/installation.sgml | 23 ++++++++++++++++-
 src/Makefile.global.in         |  2 ++
 src/include/pg_config.h.in     |  6 +++++
 src/pl/tcl/Makefile            | 12 ++++++---
 src/pl/tcl/pltcl.c             | 16 ++++++++++--
 7 files changed, 126 insertions(+), 12 deletions(-)

diff --git a/configure b/configure
index faa8b1a2e3..046fc4dcf0 100755
--- a/configure
+++ b/configure
@@ -726,6 +726,8 @@ with_python
 PERL_UNTRUSTED
 PERL_TRUSTED
 with_perl
+TCL_UNTRUSTED
+TCL_TRUSTED
 with_tcl
 ICU_LIBS
 ICU_CFLAGS
@@ -1563,7 +1565,8 @@ Optional Packages:
   --with-CC=CMD           set compiler (deprecated)
   --with-llvm             build with LLVM based JIT support
   --with-icu              build with ICU support
-  --with-tcl              build Tcl modules (PL/Tcl)
+  --with-tcl[=TRUSTWORTHINESS]
+                          build Tcl modules (PL/Tcl)
   --with-tclconfig=DIR    tclConfig.sh is in DIR
   --with-perl[=TRUSTWORTHINESS]
                           build Perl modules (PL/Perl)
@@ -8097,26 +8100,62 @@ if test "${with_tcl+set}" = set; then :
   withval=$with_tcl;
   case $withval in
     yes)
-      :
+
+  TCL_TRUSTED=yes
+  TCL_UNTRUSTED=yes
+
       ;;
     no)
       :
       ;;
     *)
-      as_fn_error $? "no argument expected for --with-tcl option" "$LINENO" 5
+      with_tcl=yes
+
+  if test "$withval" = trusted ; then
+    TCL_TRUSTED=yes
+    TCL_UNTRUSTED=no
+  elif test "$withval" = untrusted ; then
+    TCL_TRUSTED=no
+    TCL_UNTRUSTED=yes
+  else
+    as_fn_error $? "invalid --with-tcl value: argument must be omitted or specified as 'trusted' or 'untrusted'" "$LINENO" 5
+  fi
+
       ;;
   esac
 
 else
   with_tcl=no
-
 fi
 
 
+
+if test "$with_tcl" = yes; then
+
+  if test "$TCL_TRUSTED" = yes ; then
+
+$as_echo "#define USE_TCL 1" >>confdefs.h
+
+  fi
+  if test "$TCL_UNTRUSTED" = yes ; then
+
+$as_echo "#define USE_TCLU 1" >>confdefs.h
+
+  fi
+
+else
+
+  TCL_TRUSTED=no
+  TCL_UNTRUSTED=no
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $with_tcl" >&5
 $as_echo "$with_tcl" >&6; }
 
 
+
+
 # We see if the path to the Tcl/Tk configuration scripts is specified.
 # This will override the use of tclsh to find the paths to search.
 
diff --git a/configure.ac b/configure.ac
index 0dd440131b..8e7d96a6fe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -810,9 +810,39 @@ fi
 # Optionally build Tcl modules (PL/Tcl)
 #
 AC_MSG_CHECKING([whether to build with Tcl])
-PGAC_ARG_BOOL(with, tcl, no, [build Tcl modules (PL/Tcl)])
+PGAC_ARG_OPTARG(with, tcl,
+[TRUSTWORTHINESS], [build Tcl modules (PL/Tcl)],
+[
+  TCL_TRUSTED=yes
+  TCL_UNTRUSTED=yes
+],
+[
+  if test "$withval" = trusted ; then
+    TCL_TRUSTED=yes
+    TCL_UNTRUSTED=no
+  elif test "$withval" = untrusted ; then
+    TCL_TRUSTED=no
+    TCL_UNTRUSTED=yes
+  else
+    AC_MSG_ERROR([invalid --with-tcl value: argument must be omitted or specified as 'trusted' or 'untrusted'])
+  fi
+],
+[
+  if test "$TCL_TRUSTED" = yes ; then
+    AC_DEFINE([USE_TCL], 1, [Define to 1 to build with trusted Tcl support. (--with-tcl='trusted')])
+  fi
+  if test "$TCL_UNTRUSTED" = yes ; then
+    AC_DEFINE([USE_TCLU], 1, [Define to 1 to build with untrusted Tcl support. (--with-tcl='untrusted')])
+  fi
+],
+[
+  TCL_TRUSTED=no
+  TCL_UNTRUSTED=no
+])
 AC_MSG_RESULT([$with_tcl])
 AC_SUBST([with_tcl])
+AC_SUBST(TCL_TRUSTED)
+AC_SUBST(TCL_UNTRUSTED)
 
 # We see if the path to the Tcl/Tk configuration scripts is specified.
 # This will override the use of tclsh to find the paths to search.
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index 4377e9d51a..8d96152dd2 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -912,10 +912,31 @@ build-postgresql:
       </varlistentry>
 
       <varlistentry>
-       <term><option>--with-tcl</option></term>
+       <term><option>--with_tcl<optional>=<replaceable>TRUSTWORTHINESS</replaceable></optional></option></term>
        <listitem>
         <para>
          Build the <application>PL/Tcl</application> server-side language.
+         <replaceable>TRUSTWORTHINESS</replaceable> is an optional argument and,
+         if provided, must be one of:
+        </para>
+        <itemizedlist>
+         <listitem>
+          <para>
+           <option>trusted</option> to build only trusted
+           <application>PL/Tcl</application>
+          </para>
+         </listitem>
+         <listitem>
+          <para>
+           <option>untrusted</option> to build only untrusted
+           <application>PL/Tcl</application>
+           (<application>PL/TclU</application>)
+          </para>
+         </listitem>
+        </itemizedlist>
+        <para>
+         If <replaceable>TRUSTWORTHINESS</replaceable> is not specified, both
+         trusted and untrusted <application>PL/Tcl</application> will be built.
         </para>
        </listitem>
       </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 53f367ca7a..0262ee6d96 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -528,6 +528,8 @@ DEF_PGPORT = @default_port@
 WANTED_LANGUAGES = @WANTED_LANGUAGES@
 PERL_TRUSTED = @PERL_TRUSTED@
 PERL_UNTRUSTED = @PERL_UNTRUSTED@
+TCL_TRUSTED = @TCL_TRUSTED@
+TCL_UNTRUSTED = @TCL_UNTRUSTED@
 
 
 ##########################################################################
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 2779f5f671..c7eb244050 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -955,6 +955,12 @@
 /* Define to select SysV-style shared memory. */
 #undef USE_SYSV_SHARED_MEMORY
 
+/* Define to 1 to build with trusted Tcl support. (--with-tcl='trusted') */
+#undef USE_TCL
+
+/* Define to 1 to build with untrusted Tcl support. (--with-tcl='untrusted') */
+#undef USE_TCLU
+
 /* Define to select unnamed POSIX semaphores. */
 #undef USE_UNNAMED_POSIX_SEMAPHORES
 
diff --git a/src/pl/tcl/Makefile b/src/pl/tcl/Makefile
index 25e65189b6..842d425969 100644
--- a/src/pl/tcl/Makefile
+++ b/src/pl/tcl/Makefile
@@ -26,11 +26,15 @@ OBJS = \
 	$(WIN32RES) \
 	pltcl.o
 
-DATA = pltcl.control pltcl--1.0.sql \
-       pltclu.control pltclu--1.0.sql
+ifeq ($(TCL_TRUSTED), yes)
+	DATA += pltcl.control pltcl--1.0.sql
+	REGRESS_OPTS = --dbname=$(PL_TESTDB) --load-extension=pltcl
+	REGRESS = pltcl_setup pltcl_queries pltcl_trigger pltcl_call pltcl_start_proc pltcl_subxact pltcl_unicode pltcl_transaction
+endif
 
-REGRESS_OPTS = --dbname=$(PL_TESTDB) --load-extension=pltcl
-REGRESS = pltcl_setup pltcl_queries pltcl_trigger pltcl_call pltcl_start_proc pltcl_subxact pltcl_unicode pltcl_transaction
+ifeq ($(TCL_UNTRUSTED), yes)
+	DATA += pltclu.control pltclu--1.0.sql
+endif
 
 # Tcl on win32 ships with import libraries only for Microsoft Visual C++,
 # which are not compatible with mingw gcc. Therefore we need to build a
diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index 0dd6d8ab2c..57c5fc79fb 100644
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -459,6 +459,7 @@ _PG_init(void)
 	/************************************************************
 	 * Define PL/Tcl's custom GUCs
 	 ************************************************************/
+#ifdef USE_TCL
 	DefineCustomStringVariable("pltcl.start_proc",
 							   gettext_noop("PL/Tcl function to call once when pltcl is first used."),
 							   NULL,
@@ -466,6 +467,10 @@ _PG_init(void)
 							   NULL,
 							   PGC_SUSET, 0,
 							   NULL, NULL, NULL);
+	MarkGUCPrefixReserved("pltcl");
+#endif	/* USE_TCL */
+
+#ifdef USE_TCLU
 	DefineCustomStringVariable("pltclu.start_proc",
 							   gettext_noop("PL/TclU function to call once when pltclu is first used."),
 							   NULL,
@@ -473,9 +478,8 @@ _PG_init(void)
 							   NULL,
 							   PGC_SUSET, 0,
 							   NULL, NULL, NULL);
-
-	MarkGUCPrefixReserved("pltcl");
 	MarkGUCPrefixReserved("pltclu");
+#endif	/* USE_TCLU */
 
 	pltcl_pm_init_done = true;
 }
@@ -690,6 +694,8 @@ start_proc_error_callback(void *arg)
  *				  call this function for execution of
  *				  PL/Tcl procedures.
  **********************************************************************/
+#ifdef USE_TCL
+
 PG_FUNCTION_INFO_V1(pltcl_call_handler);
 
 /* keep non-static */
@@ -699,6 +705,10 @@ pltcl_call_handler(PG_FUNCTION_ARGS)
 	return pltcl_handler(fcinfo, true);
 }
 
+#endif /* USE_TCL */
+
+#ifdef USE_TCLU
+
 /*
  * Alternative handler for unsafe functions
  */
@@ -711,6 +721,8 @@ pltclu_call_handler(PG_FUNCTION_ARGS)
 	return pltcl_handler(fcinfo, false);
 }
 
+#endif	/* USE_TCLU */
+
 
 /**********************************************************************
  * pltcl_handler()		- Handler for function and trigger calls, for
-- 
2.25.1


--ReaqsoxgOBHFXBhH--





^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


--q7xzg7duksj2kgko
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0004-Introduce-pending-flag-for-GUC-assign-hooks.patch"



^ permalink  raw  reply  [nested|flat] 319+ messages in thread

* [PATCH v2 3/6] Introduce multiple shmem segments for shared buffers
@ 2025-02-24 19:08 Dmitrii Dolgov <9erthalion6@gmail.com>
  0 siblings, 0 replies; 319+ messages in thread

From: Dmitrii Dolgov @ 2025-02-24 19:08 UTC (permalink / raw)

Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status

Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.

There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
 src/backend/port/sysv_shmem.c          | 19 ++++++-
 src/backend/storage/buffer/buf_init.c  | 79 +++++++++++++++++---------
 src/backend/storage/buffer/buf_table.c |  5 +-
 src/backend/storage/buffer/freelist.c  |  4 +-
 src/backend/storage/ipc/ipci.c         |  2 +-
 src/include/storage/bufmgr.h           |  2 +-
 src/include/storage/pg_shmem.h         | 24 +++++++-
 7 files changed, 99 insertions(+), 36 deletions(-)

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 62f01d8218a..59aa67cb135 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -149,8 +149,13 @@ static int next_free_segment = 0;
  * 7f4718400000-7f4718401000 /usr/lib64/libicudata.so.74.2
  * ...
  */
-Size SHMEM_EXTRA_SIZE_LIMIT[1] = {
-	0, 									/* MAIN_SHMEM_SLOT */
+Size SHMEM_EXTRA_SIZE_LIMIT[6] = {
+	0, 									/* MAIN_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 10, 	/* BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 1024 * 1, 		/* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* BUFFER_IOCV_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+	(Size) 1024 * 1024 * 100, 			/* STRATEGY_SHMEM_SEGMENT */
 };
 
 /* Remembers offset of the last mapping from the probe address */
@@ -179,6 +184,16 @@ MappingName(int shmem_segment)
 	{
 		case MAIN_SHMEM_SEGMENT:
 			return "main";
+		case BUFFERS_SHMEM_SEGMENT:
+			return "buffers";
+		case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+			return "descriptors";
+		case BUFFER_IOCV_SHMEM_SEGMENT:
+			return "iocv";
+		case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+			return "checkpoint";
+		case STRATEGY_SHMEM_SEGMENT:
+			return "strategy";
 		default:
 			return "unknown";
 	}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1f8e03190..f5b9290a640 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -61,7 +61,10 @@ CkptSortItem *CkptBufferIds;
  * Initialize shared buffer pool
  *
  * This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
  */
 void
 BufferManagerShmemInit(void)
@@ -73,22 +76,22 @@ BufferManagerShmemInit(void)
 
 	/* Align descriptors to a cacheline boundary. */
 	BufferDescriptors = (BufferDescPadded *)
-		ShmemInitStruct("Buffer Descriptors",
+		ShmemInitStructInSegment("Buffer Descriptors",
 						NBuffers * sizeof(BufferDescPadded),
-						&foundDescs);
+						&foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
 
 	/* Align buffer pool on IO page size boundary. */
 	BufferBlocks = (char *)
 		TYPEALIGN(PG_IO_ALIGN_SIZE,
-				  ShmemInitStruct("Buffer Blocks",
+				  ShmemInitStructInSegment("Buffer Blocks",
 								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
-								  &foundBufs));
+								  &foundBufs, BUFFERS_SHMEM_SEGMENT));
 
 	/* Align condition variables to cacheline boundary. */
 	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
-		ShmemInitStruct("Buffer IO Condition Variables",
+		ShmemInitStructInSegment("Buffer IO Condition Variables",
 						NBuffers * sizeof(ConditionVariableMinimallyPadded),
-						&foundIOCV);
+						&foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,8 +101,9 @@ BufferManagerShmemInit(void)
 	 * painful.
 	 */
 	CkptBufferIds = (CkptSortItem *)
-		ShmemInitStruct("Checkpoint BufferIds",
-						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+		ShmemInitStructInSegment("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+						CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
 
 	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
 	{
@@ -153,33 +157,54 @@ BufferManagerShmemInit(void)
  * BufferManagerShmemSize
  *
  * compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
  */
 Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
 {
 	Size		size = 0;
 
-	/* size of buffer descriptors */
-	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
-	/* to allow aligning buffer descriptors */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == MAIN_SHMEM_SEGMENT)
+		return size;
 
-	/* size of data pages, plus alignment padding */
-	size = add_size(size, PG_IO_ALIGN_SIZE);
-	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+	{
+		/* size of buffer descriptors */
+		size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+		/* to allow aligning buffer descriptors */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
 
-	/* size of stuff controlled by freelist.c */
-	size = add_size(size, StrategyShmemSize());
+	if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of data pages, plus alignment padding */
+		size = add_size(size, PG_IO_ALIGN_SIZE);
+		size = add_size(size, mul_size(NBuffers, BLCKSZ));
+	}
 
-	/* size of I/O condition variables */
-	size = add_size(size, mul_size(NBuffers,
-								   sizeof(ConditionVariableMinimallyPadded)));
-	/* to allow aligning the above */
-	size = add_size(size, PG_CACHE_LINE_SIZE);
+	if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+	{
+		/* size of stuff controlled by freelist.c */
+		size = add_size(size, StrategyShmemSize());
+	}
 
-	/* size of checkpoint sort array in bufmgr.c */
-	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+	{
+		/* size of I/O condition variables */
+		size = add_size(size, mul_size(NBuffers,
+									   sizeof(ConditionVariableMinimallyPadded)));
+		/* to allow aligning the above */
+		size = add_size(size, PG_CACHE_LINE_SIZE);
+	}
+
+	if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+	{
+		/* size of checkpoint sort array in bufmgr.c */
+		size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+	}
 
 	return size;
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..ac449954dab 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -59,10 +59,11 @@ InitBufTable(int size)
 	info.entrysize = sizeof(BufferLookupEnt);
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
-	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+	SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
 								  size, size,
 								  &info,
-								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+								  STRATEGY_SHMEM_SEGMENT);
 }
 
 /*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 336715b6c63..4919a92f2be 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -491,9 +491,9 @@ StrategyInitialize(bool init)
 	 * Get or create the shared strategy control block
 	 */
 	StrategyControl = (BufferStrategyControl *)
-		ShmemInitStruct("Buffer Strategy Status",
+		ShmemInitStructInSegment("Buffer Strategy Status",
 						sizeof(BufferStrategyControl),
-						&found);
+						&found, STRATEGY_SHMEM_SEGMENT);
 
 	if (!found)
 	{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 4f6c707c204..68778522591 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -112,7 +112,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
 	size = add_size(size, DSMRegistryShmemSize());
-	size = add_size(size, BufferManagerShmemSize());
+	size = add_size(size, BufferManagerShmemSize(shmem_segment));
 	size = add_size(size, LockManagerShmemSize());
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 7c1e4316dde..bb7fe02e243 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool EvictUnpinnedBuffer(Buffer buf);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
 
 /* in localbuf.c */
 extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 138078c29c5..ba0192baf95 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
 } ShmemSegment;
 
 /* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
 
 extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
 
@@ -105,7 +105,29 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
 
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
 /* The main segment, contains everything except buffer blocks and related data. */
 #define MAIN_SHMEM_SEGMENT 0
 
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
 #endif							/* PG_SHMEM_H */
-- 
2.45.1


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