Subject: Add the ability to limit the amount of memory that can be allocated to backends.

From: Reid Thompson <[email-masked]>
Date: Wed, 31 Aug 2022 12:50:19 -0400

Hi Hackers,

Add the ability to limit the amount of memory that can be allocated to
backends.

This builds on the work that adds backend memory allocated to
pg_stat_activity
https://www.postgresql.org/message-id/67bb5c15c0489cb499723b0340f16e10c22485ec.camel%40crunchydata.com
Both patches are attached.

Add GUC variable max_total_backend_memory.

Specifies a limit to the amount of memory (MB) that may be allocated to
backends in total (i.e. this is not a per user or per backend limit).
If unset, or set to 0 it is disabled. It is intended as a resource to
help avoid the OOM killer. A backend request that would push the total
over the limit will be denied with an out of memory error causing that
backends current query/transaction to fail. Due to the dynamic nature
of memory allocations, this limit is not exact. If within 1.5MB of the
limit and two backends request 1MB each at the same time both may be
allocated exceeding the limit. Further requests will not be allocated
until dropping below the limit. Keep this in mind when setting this
value to avoid the OOM killer. Currently, this limit does not affect
auxiliary backend processes, this list of non-affected backend
processes is open for discussion as to what should/should not be
included. Backend memory allocations are displayed in the
pg_stat_activity view. 

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

[email-masked]
www.crunchydata.com
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a5cd4e44c7..caf958310a 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2079,6 +2079,32 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-max-total-backend-memory" xreflabel="max_total_backend_memory">
+      <term><varname>max_total_backend_memory</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>max_total_backend_memory</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies a limit to the amount of memory (MB) that may be allocated to
+        backends in total (i.e. this is not a per user or per backend limit).
+        If unset, or set to 0 it is disabled.  A backend request that would push
+        the total over the limit will be denied with an out of memory error
+        causing that backends current query/transaction to fail. Due to the dynamic
+        nature of memory allocations, this limit is not exact. If within 1.5MB of
+        the limit and two backends request 1MB each at the same time both may be
+        allocated exceeding the limit. Further requests will not be allocated until
+        dropping below the limit. Keep this in mind when setting this value. This
+        limit does not affect auxiliary backend processes
+        <xref linkend="glossary-auxiliary-proc"/> . Backend memory allocations
+        (<varname>backend_mem_allocated</varname>) are displayed in the
+        <link linkend="monitoring-pg-stat-activity-view"><structname>pg_stat_activity</structname></link>
+        view.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
      </sect2>
 
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 269ad2fe53..808ffe75f2 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -253,6 +253,10 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 		return true;
 	}
 
+	/* Do not exceed maximum allowed memory allocation */
+	if (op == DSM_OP_CREATE && exceeds_max_total_bkend_mem(request_size))
+		return false;
+
 	/*
 	 * Create new segment or open an existing one for attach.
 	 *
@@ -524,6 +528,10 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 		int			flags = IPCProtection;
 		size_t		segsize;
 
+		/* Do not exceed maximum allowed memory allocation */
+		if (op == DSM_OP_CREATE && exceeds_max_total_bkend_mem(request_size))
+			return false;
+
 		/*
 		 * Allocate the memory BEFORE acquiring the resource, so that we don't
 		 * leak the resource if memory allocation fails.
@@ -718,6 +726,10 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 		return true;
 	}
 
+	/* Do not exceed maximum allowed memory allocation */
+	if (op == DSM_OP_CREATE && exceeds_max_total_bkend_mem(request_size))
+		return false;
+
 	/* Create new segment or open an existing one for attach. */
 	if (op == DSM_OP_CREATE)
 	{
diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index 17a00587f8..9137a000ae 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -44,6 +44,8 @@
  */
 bool		pgstat_track_activities = false;
 int			pgstat_track_activity_query_size = 1024;
+/* Max backend memory allocation allowed (MB). 0 = disabled */
+int			max_total_bkend_mem = 0;

 /* exposed so that backend_progress.c can access it */
@@ -1253,3 +1255,107 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
 	beentry->backend_mem_allocated -= deallocation;
 	PGSTAT_END_WRITE_ACTIVITY(beentry);
 }
+
+/* ----------
+ * pgstat_get_all_backend_memory_allocated() -
+ *
+ *	Return a uint64 representing the current shared memory allocated to all
+ *	backends.  This looks directly at the BackendStatusArray, and so will
+ *	provide current information regardless of the age of our transaction's
+ *	snapshot of the status array.
+ *	In the future we will likely utilize additional values - perhaps limit
+ *	backend allocation by user/role, etc.
+ * ----------
+ */
+uint64
+pgstat_get_all_backend_memory_allocated(void)
+{
+	PgBackendStatus *beentry;
+	int			i;
+	uint64		all_backend_memory_allocated = 0;
+
+	beentry = BackendStatusArray;
+
+	/*
+	 * We probably shouldn't get here before shared memory has been set up,
+	 * but be safe.
+	 */
+	if (beentry == NULL || BackendActivityBuffer == NULL)
+		return 0;
+
+	/*
+	 * We include AUX procs in all backend memory calculation
+	 */
+	for (i = 1; i <= NumBackendStatSlots; i++)
+	{
+		/*
+		 * We use a volatile pointer here to ensure the compiler doesn't try to
+		 * get cute.
+		 */
+		volatile PgBackendStatus *vbeentry = beentry;
+		bool		found;
+		uint64		backend_mem_allocated = 0;
+
+		for (;;)
+		{
+			int			before_changecount;
+			int			after_changecount;
+
+			pgstat_begin_read_activity(vbeentry, before_changecount);
+
+			/* Ignore invalid entries, which may contain invalid data.
+			 * See pgstat_beshutdown_hook()
+			 */
+			if (vbeentry->st_procpid > 0)
+				backend_mem_allocated = vbeentry->backend_mem_allocated;
+
+			pgstat_end_read_activity(vbeentry, after_changecount);
+
+			if ((found = pgstat_read_activity_complete(before_changecount,
+													   after_changecount)))
+				break;
+
+			/* Make sure we can break out of loop if stuck... */
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		if (found)
+			all_backend_memory_allocated += backend_mem_allocated;
+
+		beentry++;
+	}
+
+	return all_backend_memory_allocated;
+}
+
+/*
+ * Determine if allocation request will exceed max backend memory allowed.
+ * Do not apply to auxiliary processes.
+ */
+bool
+exceeds_max_total_bkend_mem(uint64 allocation_request)
+{
+	bool result = false;
+
+	if (MyAuxProcType != NotAnAuxProcess)
+		return result;
+
+	/* Convert max_total_bkend_mem to bytes for comparison */
+	if (max_total_bkend_mem &&
+		pgstat_get_all_backend_memory_allocated() +
+		allocation_request > (uint64)max_total_bkend_mem * 1024 * 1024)
+	{
+		/*
+		 * Explicitely identify the OOM being a result of this
+		 * configuration parameter vs a system failure to allocate OOM.
+		 */
+		elog(WARNING,
+			 "request will exceed postgresql.conf defined max_total_backend_memory limit (%lu > %lu)",
+			 pgstat_get_all_backend_memory_allocated() +
+			 allocation_request, (uint64)max_total_bkend_mem * 1024 * 1024);
+
+		result = true;
+	}
+
+	return result;
+}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 9fbbfb1be5..ab8d83c235 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -3664,6 +3664,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"max_total_backend_memory", PGC_SIGHUP, RESOURCES_MEM,
+			gettext_noop("Restrict total backend memory allocations to this max."),
+			gettext_noop("0 turns this feature off."),
+			GUC_UNIT_MB
+		},
+		&max_total_bkend_mem,
+		0, 0, INT_MAX,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 90bec0502c..8e944f6511 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -155,6 +155,9 @@
 					#   mmap
 					# (change requires restart)
 #min_dynamic_shared_memory = 0MB	# (change requires restart)
+#max_total_backend_memory = 0MB		# Restrict total backend memory allocations
+									# to this max (in MB). 0 turns this feature
+									# off.
 
 # - Disk -
 
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index c91f8efa4d..ac9a1ced3f 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -428,6 +428,10 @@ AllocSetContextCreateInternal(MemoryContext parent,
 	else
 		firstBlockSize = Max(firstBlockSize, initBlockSize);
 
+	/* Do not exceed maximum allowed memory allocation */
+	if (exceeds_max_total_bkend_mem(firstBlockSize))
+		return NULL;
+
 	/*
 	 * Allocate the initial block.  Unlike other aset.c blocks, it starts with
 	 * the context header and its block header follows that.
@@ -720,6 +724,11 @@ AllocSetAlloc(MemoryContext context, Size size)
 	{
 		chunk_size = MAXALIGN(size);
 		blksize = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
+
+		/* Do not exceed maximum allowed memory allocation */
+		if (exceeds_max_total_bkend_mem(blksize))
+			return NULL;
+
 		block = (AllocBlock) malloc(blksize);
 		if (block == NULL)
 			return NULL;
@@ -911,6 +920,10 @@ AllocSetAlloc(MemoryContext context, Size size)
 		while (blksize < required_size)
 			blksize <<= 1;
 
+		/* Do not exceed maximum allowed memory allocation */
+		if (exceeds_max_total_bkend_mem(blksize))
+			return NULL;
+
 		/* Try to allocate it */
 		block = (AllocBlock) malloc(blksize);
 
@@ -1133,6 +1146,10 @@ AllocSetRealloc(void *pointer, Size size)
 		blksize = chksize + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
 		oldblksize = block->endptr - ((char *) block);
 
+		/* Do not exceed maximum allowed memory allocation */
+		if (blksize > oldblksize && exceeds_max_total_bkend_mem(blksize - oldblksize))
+			return NULL;
+
 		block = (AllocBlock) realloc(block, blksize);
 		if (block == NULL)
 		{
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index 36e5b3f94d..1d5720836c 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -192,6 +192,9 @@ GenerationContextCreate(MemoryContext parent,
 	else
 		allocSize = Max(allocSize, initBlockSize);
 
+	if (exceeds_max_total_bkend_mem(allocSize))
+		return NULL;
+
 	/*
 	 * Allocate the initial block.  Unlike other generation.c blocks, it
 	 * starts with the context header and its block header follows that.
@@ -361,6 +364,9 @@ GenerationAlloc(MemoryContext context, Size size)
 	{
 		Size		blksize = required_size + Generation_BLOCKHDRSZ;
 
+		if (exceeds_max_total_bkend_mem(blksize))
+			return NULL;
+
 		block = (GenerationBlock *) malloc(blksize);
 		if (block == NULL)
 			return NULL;
@@ -464,6 +470,9 @@ GenerationAlloc(MemoryContext context, Size size)
 			if (blksize < required_size)
 				blksize = pg_nextpower2_size_t(required_size);
 
+			if (exceeds_max_total_bkend_mem(blksize))
+				return NULL;
+
 			block = (GenerationBlock *) malloc(blksize);
 
 			if (block == NULL)
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index efc8bcfaa7..5cf0cfff86 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -177,6 +177,10 @@ SlabContextCreate(MemoryContext parent,
 	headerSize += chunksPerBlock * sizeof(bool);
 #endif
 
+	/* Do not exceed maximum allowed memory allocation */
+	if (exceeds_max_total_bkend_mem(headerSize))
+		return NULL;
+
 	slab = (SlabContext *) malloc(headerSize);
 	if (slab == NULL)
 	{
@@ -331,6 +335,10 @@ SlabAlloc(MemoryContext context, Size size)
 	 */
 	if (slab->minFreeChunks == 0)
 	{
+		/* Do not exceed maximum allowed memory allocation */
+		if (exceeds_max_total_bkend_mem(slab->blockSize))
+			return NULL;
+
 		block = (SlabBlock *) malloc(slab->blockSize);
 
 		if (block == NULL)
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index 9bdc4197bd..3b940ff98e 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -270,6 +270,7 @@ typedef struct LocalPgBackendStatus
  */
 extern PGDLLIMPORT bool pgstat_track_activities;
 extern PGDLLIMPORT int pgstat_track_activity_query_size;
+extern PGDLLIMPORT int max_total_bkend_mem;

 /* ----------
@@ -321,6 +322,7 @@ extern int	pgstat_fetch_stat_numbackends(void);
 extern PgBackendStatus *pgstat_fetch_stat_beentry(int beid);
 extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 extern char *pgstat_clip_activity(const char *raw_activity);
+extern bool exceeds_max_total_bkend_mem(uint64 allocation_request);

 #endif							/* BACKEND_STATUS_H */
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 1d9509a2f6..40ae638f25 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -947,6 +947,18 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
      </para></entry>
     </row>
 
+    <row>
+     <entry role="catalog_table_entry"><para role="column_definition">
+      <structfield>backend_mem_allocated</structfield> <type>bigint</type>
+     </para>
+     <para>
+      The byte count of memory allocated to this backend. Dynamic shared memory
+      allocations are included only in the value displayed for the backend that
+      created them, they are not included in the value for backends that are
+      attached to them to avoid double counting.
+     </para></entry>
+    </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>query</structfield> <type>text</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 5a844b63a1..d23f0e9dbb 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -863,6 +863,7 @@ CREATE VIEW pg_stat_activity AS
             S.backend_xid,
             s.backend_xmin,
             S.query_id,
+            S.backend_mem_allocated,
             S.query,
             S.backend_type
     FROM pg_stat_get_activity(NULL) AS S
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index e1b90c5de4..269ad2fe53 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -66,6 +66,7 @@
 #include "postmaster/postmaster.h"
 #include "storage/dsm_impl.h"
 #include "storage/fd.h"
+#include "utils/backend_status.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 
@@ -232,6 +233,13 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pgstat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_mem_allocated_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && shm_unlink(name) != 0)
@@ -332,6 +340,36 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pgstat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+	{
+		/*
+		 * Posix creation calls dsm_impl_posix_resize implying that resizing
+		 * occurs or may be added in the future. As implemented
+		 * dsm_impl_posix_resize utilizes fallocate or truncate, passing the
+		 * whole new size as input, growing the allocation as needed * (only
+		 * truncate supports shrinking). We update by replacing the * old
+		 * allocation with the new.
+		 */
+#if defined(HAVE_POSIX_FALLOCATE) && defined(__linux__)
+		/*
+		 * posix_fallocate does not shrink allocations, adjust only on
+		 * allocation increase.
+		 */
+		if (request_size > *mapped_size)
+		{
+			pgstat_report_backend_mem_allocated_decrease(*mapped_size);
+			pgstat_report_backend_mem_allocated_increase(request_size);
+		}
+#else
+		pgstat_report_backend_mem_allocated_decrease(*mapped_size);
+		pgstat_report_backend_mem_allocated_increase(request_size);
+#endif
+	}
 	*mapped_address = address;
 	*mapped_size = request_size;
 	close(fd);
@@ -537,6 +575,14 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pgstat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_mem_allocated_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && shmctl(ident, IPC_RMID, NULL) < 0)
@@ -584,6 +630,13 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pgstat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_mem_allocated_increase(request_size);
 	*mapped_address = address;
 	*mapped_size = request_size;
 
@@ -652,6 +705,13 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 			return false;
 		}
 
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pgstat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_mem_allocated_decrease(*mapped_size);
 		*impl_private = NULL;
 		*mapped_address = NULL;
 		*mapped_size = 0;
@@ -768,6 +828,12 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 		return false;
 	}
 
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pgstat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_mem_allocated_increase(info.RegionSize);
 	*mapped_address = address;
 	*mapped_size = info.RegionSize;
 	*impl_private = hmap;
@@ -812,6 +878,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pgstat_activity when the creator destroys the
+		 * allocation.
+		 */
+		pgstat_report_backend_mem_allocated_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && unlink(name) != 0)
@@ -933,6 +1006,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pgstat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_mem_allocated_increase(request_size);
 	*mapped_address = address;
 	*mapped_size = request_size;
 
diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index c7ed1e6d7a..17a00587f8 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -49,6 +49,8 @@ int			pgstat_track_activity_query_size = 1024;
 /* exposed so that backend_progress.c can access it */
 PgBackendStatus *MyBEEntry = NULL;
 
+/* Memory allocated to this backend prior to pgstats initialization */
+uint64		backend_mem_allocated = 0;
 
 static PgBackendStatus *BackendStatusArray = NULL;
 static char *BackendAppnameBuffer = NULL;
@@ -400,6 +402,13 @@ pgstat_bestart(void)
 	lbeentry.st_progress_command_target = InvalidOid;
 	lbeentry.st_query_id = UINT64CONST(0);
 
+	/*
+	 * Move sum of memory allocated prior to pgstats initialization to pgstats
+	 * and zero the local variable.
+	 */
+	lbeentry.backend_mem_allocated = backend_mem_allocated;
+	backend_mem_allocated = 0;
+
 	/*
 	 * we don't zero st_progress_param here to save cycles; nobody should
 	 * examine it until st_progress_command has been set to something other
@@ -1148,3 +1157,99 @@ pgstat_clip_activity(const char *raw_activity)
 
 	return activity;
 }
+
+/* --------
+ * pgstat_report_backend_mem_allocated_increase() -
+ *
+ * Called to report increase in memory allocated for this backend
+ * --------
+ */
+void
+pgstat_report_backend_mem_allocated_increase(uint64 allocation)
+{
+	volatile PgBackendStatus *beentry = MyBEEntry;
+
+	if (!beentry || !pgstat_track_activities)
+	{
+		/*
+		 * Account for memory before pgstats is initialized. This will be
+		 * migrated to pgstats on initialization.
+		 */
+		backend_mem_allocated += allocation;
+
+		return;
+	}
+
+	/*
+	 * Update my status entry, following the protocol of bumping
+	 * st_changecount before and after.  We use a volatile pointer here to
+	 * ensure the compiler doesn't try to get cute.
+	 */
+	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
+	beentry->backend_mem_allocated += allocation;
+	PGSTAT_END_WRITE_ACTIVITY(beentry);
+}
+
+/* --------
+ * pgstat_report_backend_mem_allocated_decrease() -
+ *
+ * Called to report decrease in memory allocated for this backend
+ * --------
+ */
+void
+pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
+{
+	volatile PgBackendStatus *beentry = MyBEEntry;
+
+	/*
+	 * Cases may occur where shared memory from a previous postmaster
+	 * invocation still exist. These are cleaned up at startup by
+	 * dsm_cleanup_using_control_segment. Limit decreasing memory allocated to
+	 * zero in case no corresponding prior increase exists or decrease has
+	 * already been accounted for.
+	 */
+
+	if (!beentry || !pgstat_track_activities)
+	{
+		/*
+		 * Account for memory before pgstats is initialized. This will be
+		 * migrated to pgstats on initialization. Do not allow
+		 * backend_mem_allocated to go below zero. If pgstats has not been
+		 * initialized, we are in startup and we set backend_mem_allocated to
+		 * zero in cases where it would go negative and skip generating an
+		 * ereport.
+		 */
+		if (deallocation > backend_mem_allocated)
+			backend_mem_allocated = 0;
+		else
+			backend_mem_allocated -= deallocation;
+
+		return;
+	}
+
+	/*
+	 * Do not allow backend_mem_allocated to go below zero. ereport if we
+	 * would have. There's no need for a lock around the read here asit's
+	 * being referenced from the same backend which means that there shouldn't
+	 * be concurrent writes. We want to generate an ereport in these cases.
+	 */
+	if (deallocation > beentry->backend_mem_allocated)
+	{
+		ereport(LOG, (errmsg("decrease reduces reported backend memory allocated below zero; setting reported to 0")));
+
+		/*
+		 * Overwrite deallocation with current backend_mem_allocated so we end
+		 * up at zero.
+		 */
+		deallocation = beentry->backend_mem_allocated;
+	}
+
+	/*
+	 * Update my status entry, following the protocol of bumping
+	 * st_changecount before and after.  We use a volatile pointer here to
+	 * ensure the compiler doesn't try to get cute.
+	 */
+	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
+	beentry->backend_mem_allocated -= deallocation;
+	PGSTAT_END_WRITE_ACTIVITY(beentry);
+}
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 4cca30aae7..1574aa8049 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -536,7 +536,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_activity(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_ACTIVITY_COLS	30
+#define PG_STAT_GET_ACTIVITY_COLS	31
 	int			num_backends = pgstat_fetch_stat_numbackends();
 	int			curr_backend;
 	int			pid = PG_ARGISNULL(0) ? -1 : PG_GETARG_INT32(0);
@@ -610,6 +610,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[16] = true;
 
+		values[30] = UInt64GetDatum(beentry->backend_mem_allocated);
+
 		/* Values only available to role member or pg_read_all_stats */
 		if (HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		{
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index b6eeb8abab..c91f8efa4d 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -47,6 +47,7 @@
 #include "postgres.h"
 
 #include "port/pg_bitutils.h"
+#include "utils/backend_status.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
 #include "utils/memutils_memorychunk.h"
@@ -509,6 +510,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 						name);
 
 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_backend_mem_allocated_increase(firstBlockSize);
 
 	return (MemoryContext) set;
 }
@@ -532,6 +534,7 @@ AllocSetReset(MemoryContext context)
 	AllocBlock	block;
 	Size		keepersize PG_USED_FOR_ASSERTS_ONLY
 	= set->keeper->endptr - ((char *) set);
+	uint64		deallocation = 0;
 
 	AssertArg(AllocSetIsValid(set));
 
@@ -571,6 +574,7 @@ AllocSetReset(MemoryContext context)
 		{
 			/* Normal case, release the block */
 			context->mem_allocated -= block->endptr - ((char *) block);
+			deallocation += block->endptr - ((char *) block);
 
 #ifdef CLOBBER_FREED_MEMORY
 			wipe_mem(block, block->freeptr - ((char *) block));
@@ -581,6 +585,7 @@ AllocSetReset(MemoryContext context)
 	}
 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_backend_mem_allocated_decrease(deallocation);
 
 	/* Reset block size allocation sequence, too */
 	set->nextBlockSize = set->initBlockSize;
@@ -600,6 +605,7 @@ AllocSetDelete(MemoryContext context)
 	AllocBlock	block = set->blocks;
 	Size		keepersize PG_USED_FOR_ASSERTS_ONLY
 	= set->keeper->endptr - ((char *) set);
+	uint64		deallocation = 0;
 
 	AssertArg(AllocSetIsValid(set));
 
@@ -635,11 +641,13 @@ AllocSetDelete(MemoryContext context)
 
 				freelist->first_free = (AllocSetContext *) oldset->header.nextchild;
 				freelist->num_free--;
+				deallocation += oldset->header.mem_allocated;
 
 				/* All that remains is to free the header/initial block */
 				free(oldset);
 			}
 			Assert(freelist->num_free == 0);
+			pgstat_report_backend_mem_allocated_decrease(deallocation);
 		}
 
 		/* Now add the just-deleted context to the freelist. */
@@ -656,7 +664,10 @@ AllocSetDelete(MemoryContext context)
 		AllocBlock	next = block->next;
 
 		if (block != set->keeper)
+		{
 			context->mem_allocated -= block->endptr - ((char *) block);
+			deallocation += block->endptr - ((char *) block);
+		}
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -669,6 +680,8 @@ AllocSetDelete(MemoryContext context)
 	}
 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_backend_mem_allocated_decrease(deallocation +
+												 context->mem_allocated);
 
 	/* Finally, free the context header, including the keeper block */
 	free(set);
@@ -712,6 +725,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;
 
 		context->mem_allocated += blksize;
+		pgstat_report_backend_mem_allocated_increase(blksize);
 
 		block->aset = set;
 		block->freeptr = block->endptr = ((char *) block) + blksize;
@@ -916,6 +930,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;
 
 		context->mem_allocated += blksize;
+		pgstat_report_backend_mem_allocated_increase(blksize);
 
 		block->aset = set;
 		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -1016,6 +1031,7 @@ AllocSetFree(void *pointer)
 			block->next->prev = block->prev;
 
 		set->header.mem_allocated -= block->endptr - ((char *) block);
+		pgstat_report_backend_mem_allocated_decrease(block->endptr - ((char *) block));
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -1127,7 +1143,9 @@ AllocSetRealloc(void *pointer, Size size)
 
 		/* updated separately, not to underflow when (oldblksize > blksize) */
 		set->header.mem_allocated -= oldblksize;
+		pgstat_report_backend_mem_allocated_decrease(oldblksize);
 		set->header.mem_allocated += blksize;
+		pgstat_report_backend_mem_allocated_increase(blksize);
 
 		block->freeptr = block->endptr = ((char *) block) + blksize;
 
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index b39894ec94..36e5b3f94d 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"
 #include "port/pg_bitutils.h"
+#include "utils/backend_status.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
 #include "utils/memutils_memorychunk.h"
@@ -258,6 +259,7 @@ GenerationContextCreate(MemoryContext parent,
 						name);
 
 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_backend_mem_allocated_increase(firstBlockSize);
 
 	return (MemoryContext) set;
 }
@@ -274,6 +276,7 @@ GenerationReset(MemoryContext context)
 {
 	GenerationContext *set = (GenerationContext *) context;
 	dlist_mutable_iter miter;
+	uint64	deallocation = 0;
 
 	AssertArg(GenerationIsValid(set));
 
@@ -296,9 +299,14 @@ GenerationReset(MemoryContext context)
 		if (block == set->keeper)
 			GenerationBlockMarkEmpty(block);
 		else
+		{
+			deallocation += block->blksize;
 			GenerationBlockFree(set, block);
+		}
 	}
 
+	pgstat_report_backend_mem_allocated_decrease(deallocation);
+
 	/* set it so new allocations to make use of the keeper block */
 	set->block = set->keeper;
 
@@ -319,6 +327,9 @@ GenerationDelete(MemoryContext context)
 {
 	/* Reset to release all releasable GenerationBlocks */
 	GenerationReset(context);
+
+	pgstat_report_backend_mem_allocated_decrease(context->mem_allocated);
+
 	/* And free the context header and keeper block */
 	free(context);
 }
@@ -355,6 +366,7 @@ GenerationAlloc(MemoryContext context, Size size)
 			return NULL;
 
 		context->mem_allocated += blksize;
+		pgstat_report_backend_mem_allocated_increase(blksize);
 
 		/* block with a single (used) chunk */
 		block->context = set;
@@ -458,6 +470,7 @@ GenerationAlloc(MemoryContext context, Size size)
 				return NULL;
 
 			context->mem_allocated += blksize;
+			pgstat_report_backend_mem_allocated_increase(blksize);
 
 			/* initialize the new block */
 			GenerationBlockInit(set, block, blksize);
@@ -691,6 +704,8 @@ GenerationFree(void *pointer)
 	dlist_delete(&block->node);
 
 	set->header.mem_allocated -= block->blksize;
+	pgstat_report_backend_mem_allocated_decrease(block->blksize);
+
 	free(block);
 }
 
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 2d70adef09..efc8bcfaa7 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
+#include "utils/backend_status.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
 #include "utils/memutils_memorychunk.h"
@@ -218,6 +219,12 @@ SlabContextCreate(MemoryContext parent,
 						parent,
 						name);
 
+	/*
+	 * If SlabContextCreate is updated to add headerSize to
+	 * context->mem_allocated, then update here and SlabDelete appropriately
+	 */
+	pgstat_report_backend_mem_allocated_increase(headerSize);
+
 	return (MemoryContext) slab;
 }
 
@@ -233,6 +240,7 @@ SlabReset(MemoryContext context)
 {
 	int			i;
 	SlabContext *slab = castNode(SlabContext, context);
+	uint64		deallocation = 0;
 
 	Assert(slab);
 
@@ -258,9 +266,11 @@ SlabReset(MemoryContext context)
 			free(block);
 			slab->nblocks--;
 			context->mem_allocated -= slab->blockSize;
+			deallocation += slab->blockSize;
 		}
 	}
 
+	pgstat_report_backend_mem_allocated_decrease(deallocation);
 	slab->minFreeChunks = 0;
 
 	Assert(slab->nblocks == 0);
@@ -274,8 +284,17 @@ SlabReset(MemoryContext context)
 void
 SlabDelete(MemoryContext context)
 {
+	/*
+	 * Until header allocation is included in context->mem_allocated cast to
+	 * slab and decrement the headerSize
+	 */
+	SlabContext *slab = castNode(SlabContext, context);
+
 	/* Reset to release all the SlabBlocks */
 	SlabReset(context);
+
+	pgstat_report_backend_mem_allocated_decrease(slab->headerSize);
+
 	/* And free the context header */
 	free(context);
 }
@@ -344,6 +363,7 @@ SlabAlloc(MemoryContext context, Size size)
 		slab->minFreeChunks = slab->chunksPerBlock;
 		slab->nblocks += 1;
 		context->mem_allocated += slab->blockSize;
+		pgstat_report_backend_mem_allocated_increase(slab->blockSize);
 	}
 
 	/* grab the block from the freelist (even the new block is there) */
@@ -511,6 +531,7 @@ SlabFree(void *pointer)
 		free(block);
 		slab->nblocks--;
 		slab->header.mem_allocated -= slab->blockSize;
+		pgstat_report_backend_mem_allocated_decrease(slab->blockSize);
 	}
 	else
 		dlist_push_head(&slab->freelist[block->nfree], &block->node);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index be47583122..e1bfb85b25 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5340,9 +5340,9 @@
   proname => 'pg_stat_get_activity', prorows => '100', proisstrict => 'f',
   proretset => 't', provolatile => 's', proparallel => 'r',
   prorettype => 'record', proargtypes => 'int4',
-  proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,text,numeric,text,bool,text,bool,int4,int8}',
-  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id}',
+  proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,text,numeric,text,bool,text,bool,int4,int8,int8}',
+  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id,backend_mem_allocated}',
   prosrc => 'pg_stat_get_activity' },
 { oid => '3318',
   descr => 'statistics: information about progress of backends running maintenance command',
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index 7403bca25e..9bdc4197bd 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -168,6 +168,9 @@ typedef struct PgBackendStatus
 
 	/* query identifier, optionally computed using post_parse_analyze_hook */
 	uint64		st_query_id;
+
+	/* Current memory allocated to this backend */
+	uint64		backend_mem_allocated;
 } PgBackendStatus;

@@ -305,7 +308,9 @@ extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
 extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
 													   int buflen);
 extern uint64 pgstat_get_my_query_id(void);
-
+extern void pgstat_report_backend_mem_allocated_increase(uint64 allocation);
+extern void pgstat_report_backend_mem_allocated_decrease(uint64 deallocation);
+extern uint64 pgstat_get_all_backend_memory_allocated(void);
 
 /* ----------
  * Support functions for the SQL-callable functions to
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 7ec3d2688f..674e5c6fe7 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1757,9 +1757,10 @@ pg_stat_activity| SELECT s.datid,
     s.backend_xid,
     s.backend_xmin,
     s.query_id,
+    s.backend_mem_allocated,
     s.query,
     s.backend_type
-   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_mem_allocated)
      LEFT JOIN pg_database d ON ((s.datid = d.oid)))
      LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
 pg_stat_all_indexes| SELECT c.oid AS relid,
@@ -1871,7 +1872,7 @@ pg_stat_gssapi| SELECT s.pid,
     s.gss_auth AS gss_authenticated,
     s.gss_princ AS principal,
     s.gss_enc AS encrypted
-   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_mem_allocated)
   WHERE (s.client_port IS NOT NULL);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
@@ -2052,7 +2053,7 @@ pg_stat_replication| SELECT s.pid,
     w.sync_priority,
     w.sync_state,
     w.reply_time
-   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_mem_allocated)
      JOIN pg_stat_get_wal_senders() w(pid, state, sent_lsn, write_lsn, flush_lsn, replay_lsn, write_lag, flush_lag, replay_lag, sync_priority, sync_state, reply_time) ON ((s.pid = w.pid)))
      LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
 pg_stat_replication_slots| SELECT s.slot_name,
@@ -2086,7 +2087,7 @@ pg_stat_ssl| SELECT s.pid,
     s.ssl_client_dn AS client_dn,
     s.ssl_client_serial AS client_serial,
     s.ssl_issuer_dn AS issuer_dn
-   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_mem_allocated)
   WHERE (s.client_port IS NOT NULL);
 pg_stat_subscription| SELECT su.oid AS subid,
     su.subname,

---

From: Justin Pryzby <[email-masked]>
Date: Wed, 31 Aug 2022 12:34:57 -0500

> Both patches are attached.

You should name the patches with different prefixes, like
001,002,003  Otherwise, cfbot may try to apply them in the wrong order.
git format-patch is the usual tool for that.

> +        Specifies a limit to the amount of memory (MB) that may be allocated to

MB are just the default unit, right ?
The user should be allowed to write max_total_backend_memory='2GB'

> +        causing that backends current query/transaction to fail. Due to the dynamic

backend's

> +        allocated exceeding the limit. Further requests will not be allocated until

allocated, and exceed the limit

> +	if (MyAuxProcType != NotAnAuxProcess)

The double negative is confusing, so could use a comment.

> +			 allocation_request, (uint64)max_total_bkend_mem * 1024 * 1024);

I think it should be ereport() rather than elog(), which is
internal-only, and not-translated.

> +                       gettext_noop("0 turns this feature off."),

I think this needs a maximum like INT_MAX/1024/1024

> +pgstat_get_all_backend_memory_allocated(void)
...
> +	for (i = 1; i <= NumBackendStatSlots; i++)

It's looping over every backend for each allocation.
Do you know if there's any performance impact of that ?

I think it may be necessary to track the current allocation size in
shared memory (with atomic increments?).  Maybe decrements would need to
be exactly accounted for, or otherwise Assert() that the value is not
negative.  I don't know how expensive it'd be to have conditionals for
each decrement, but maybe the value would only be decremented at
strategic times, like at transaction commit or backend shutdown.

-- 
Justin

---

From: Kyotaro Horiguchi <[email-masked]>
Date: Thu, 01 Sep 2022 11:48:40 +0900 (JST)

At Wed, 31 Aug 2022 12:50:19 -0400, Reid Thompson <[email-masked]> wrote in 
> Add the ability to limit the amount of memory that can be allocated to

The patch seems to limit both of memory-context allocations and DSM
allocations happen on a specific process by the same budget. In the
fist place I don't think it's sensible to cap the amount of DSM
allocations by per-process budget.

DSM is used by pgstats subsystem. There can be cases where pgstat
complains for denial of DSM allocation after the budget has been
exhausted by memory-context allocations, or every command complains
for denial of memory-context allocation after once the per-process
budget is exhausted by DSM allocations. That doesn't seem reasonable.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

---

From: "Drouvot, Bertrand" <[email-masked]>
Date: Fri, 2 Sep 2022 09:30:21 +0200

Hi,

> Add the ability to limit the amount of memory that can be allocated to

Thanks for the patch.

+ 1 on the idea.

> backends current query/transaction to fail.

I'm not sure we are choosing the right victims here (aka the ones that 
are doing the request that will push the total over the limit).

Imagine an extreme case where a single backend consumes say 99% of the 
limit, shouldn't it be the one to be "punished"? (and somehow forced to 
give the memory back).

The problem that i see with the current approach is that a "bad" backend 
could impact all the others and continue to do so.

what about punishing say the highest consumer , what do you think? (just 
speaking about the general idea here, not about the implementation)

Regards,

-- 

Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

---

From: David Rowley <[email-masked]>
Date: Fri, 2 Sep 2022 20:52:54 +1200

> Add the ability to limit the amount of memory that can be allocated to

Are you aware that relcache entries are stored in backend local memory
and that once we've added a relcache entry for a relation that we have
no current code which attempts to reduce the memory consumption used
by cache entries when there's memory pressure?

It seems to me that if we had this feature as you propose that a
backend could hit the limit and stay there just from the memory
requirements of the relation cache after some number of tables have
been accessed from the given backend. It's not hard to imagine a
situation where the palloc() would start to fail during parse, which
might make it quite infuriating for anyone trying to do something
like:

SET max_total_backend_memory TO 0;

or

ALTER SYSTEM SET max_total_backend_memory TO 0;

I think a better solution to this problem would be to have "memory
grants", where we configure some amount of "pool" memory that backends
are allowed to use for queries.  The planner would have to add the
expected number of work_mem that the given query is expected to use
and before that query starts, the executor would have to "checkout"
that amount of memory from the pool and return it when finished.  If
there is not enough memory in the pool then the query would have to
wait until enough memory is available.   This creates a deadlocking
hazard that the deadlock detector would need to be made aware of.

I know Thomas Munro has mentioned this "memory grant" or "memory pool"
feature to me previously and I think he even has some work in progress
code for it.  It's a very tricky problem, however, as aside from the
deadlocking issue, it requires working out how much memory a given
plan will use concurrently. That's not as simple as counting the nodes
that use work_mem and summing those up.

There is some discussion about the feature in [1]. I was unable to
find what Thomas mentioned on the list about this. I've included him
here in case he has any extra information to share.

David

[1] https://www.postgresql.org/message-id/flat/20220713222342.GE18011%40telsasoft.com#b4f526aa8f2c893567c1ecf069f9e6c7

---

From: Reid Thompson <[email-masked]>
Date: Sat, 03 Sep 2022 23:40:03 -0400

> git format-patch is the usual tool for that.

Thanks for the pointer. My experience with git in the past has been
minimal and basic.

> The user should be allowed to write max_total_backend_memory='2GB'

Correct. Default units are MB. Other unit types are converted to MB.

> > +        causing that backends current query/transaction to fail.
> 
> backend's
> > +        allocated exceeding the limit. Further requests will not
> 

> internal-only, and not-translated.

Corrected/added the the above items. Attached patches with the corrections.

> I think this needs a maximum like INT_MAX/1024/1024

Is this noting that we'd set a ceiling of 2048MB?

> Do you know if there's any performance impact of that ?

I'm not very familiar with how to test performance impact, I'm open to
suggestions.  I have performed the below pgbench tests and noted the basic
tps differences in the table.

Test 1:
branch master
CFLAGS="-I/usr/include/python3.8/ " /home/rthompso/src/git/postgres/configure --silent --prefix=/home/rthompso/src/git/postgres/install/master --with-openssl --with-tcl --with-tclconfig=/usr/lib/tcl8.6 --with-perl --with-libxml --with-libxslt --with-python --with-gssapi --with-systemd --with-ldap --enable-nls
make -s -j12 && make -s install
initdb
default postgresql.conf settings
init pgbench pgbench -U rthompso -p 5433 -h localhost -i -s 50 testpgbench
10 iterations
for ctr in {1..10}; do     { time pgbench  -p 5433 -h localhost -c 10 -j 10 -t 50000 testpgbench; } 2>&1 | tee -a pgstatsResultsNoLimitSet; done

Test 2:
branch pg-stat-activity-backend-memory-allocated
CFLAGS="-I/usr/include/python3.8/ " /home/rthompso/src/git/postgres/configure --silent --prefix=/home/rthompso/src/git/postgres/install/pg-stats-memory/ --with-openssl --with-tcl --with-tclconfig=/usr/lib/tcl8.6 --with-perl --with-libxml --with-libxslt --with-python --with-gssapi --with-systemd --with-ldap --enable-nls
make -s -j12 && make -s install
initdb 
default postgresql.conf settings
init pgbench pgbench -U rthompso -p 5433 -h localhost -i -s 50
testpgbench
10 iterations
for ctr in {1..10}; do     { time pgbench  -p 5433 -h localhost -c 10  -j 10 -t 50000 testpgbench; } 2>&1 | tee -a pgstatsResultsPg-stats-memory; done

Test 3:
branch dev-max-memory
CFLAGS="-I/usr/include/python3.8/ " /home/rthompso/src/git/postgres/configure --silent --prefix=/home/rthompso/src/git/postgres/install/dev-max-memory/ --with-openssl --with-tcl --with-tclconfig=/usr/lib/tcl8.6 --with-perl --with-libxml --with-libxslt --with-python --with-gssapi --with-systemd --with-ldap --enable-nls
make -s -j12 && make -s install
initdb 
default postgresql.conf settings
init pgbench pgbench -U rthompso -p 5433 -h localhost -i -s 50 testpgbench
10 iterations
for ctr in {1..10}; do     { time pgbench  -p 5433 -h localhost -c 10  -j 10 -t 50000 testpgbench; } 2>&1 | tee -a pgstatsResultsDev-max-memory; done

Test 4:
branch dev-max-memory
CFLAGS="-I/usr/include/python3.8/ " /home/rthompso/src/git/postgres/configure --silent --prefix=/home/rthompso/src/git/postgres/install/dev-max-memory/ --with-openssl --with-tcl --with-tclconfig=/usr/lib/tcl8.6 --with-perl --with-libxml --with-libxslt --with-python --with-gssapi --with-systemd --with-ldap --enable-nls
make -s -j12 && make -s install
initdb 
non-default postgresql.conf setting for max_total_backend_memory = 100MB
init pgbench pgbench -U rthompso -p 5433 -h localhost -i -s 50 testpgbench
10 iterations
for ctr in {1..10}; do     { time pgbench  -p 5433 -h localhost -c 10  -j 10 -t 50000 testpgbench; } 2>&1 | tee -a pgstatsResultsDev-max-memory100MB; done

Laptop
11th Gen Intel(R) Core(TM) i7-11850H @ 2.50GHz 8 Cores 16 threads
32GB RAM
SSD drive

Averages from the 10 runs and tps difference over the 10 runs
|------------------+------------------+------------------------+-------------------+------------------+-------------------+---------------+------------------|
| Test Run         | Master           | Track Memory Allocated | Diff from Master  | Max Mem off      | Diff from Master  | Max Mem 100MB | Diff from Master |
| Set 1            | Test 1           | Test 2                 |                   | Test 3           |                   | Test 4        |                  |
| latency average  | 2.43390909090909 | 2.44327272727273       |                   | 2.44381818181818 |                   | 2.6843        |                  |
| tps inc conn est | 3398.99291372727 | 3385.40984336364       | -13.583070363637  | 3385.08184309091 | -13.9110706363631 | 3729.5363413  | 330.54342757273  |
| tps exc conn est | 3399.12185727273 | 3385.52527490909       | -13.5965823636366 | 3385.22100872727 | -13.9008485454547 | 3729.7097607  | 330.58790342727  |
|------------------+------------------+------------------------+-------------------+------------------+-------------------+---------------+------------------|
| Set 2            |                  |                        |                   |                  |                   |               |                  |
| latency average  | 2.691            | 2.6895                 | 2                 | 2.69             | 3                 | 2.6827        | 4                |
| tps inc conn est | 3719.56          | 3721.7587106           | 2.1987106         | 3720.3           | .74               | 3730.86       | 11.30            |
| tps exc conn est | 3719.71          | 3721.9268465           | 2.2168465         | 3720.47          | .76               | 3731.02       | 11.31            |
|------------------+------------------+------------------------+-------------------+------------------+-------------------+---------------+------------------|

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

[email-masked]
www.crunchydata.com
From 57a79b5f72af510f8c4b9ea65f5ffb4fe1fb7798 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Sat, 4 Jun 2022 22:23:59 -0400
Subject: [PATCH 2/2] Add the ability to limit the amount of memory that can be
 allocated to backends.

This builds on the work that adds backend memory allocated to pg_stat_activity.

Specifies a limit to the amount of memory (MB) that may be allocated to backends
in total (i.e. this is not a per user or per backend limit). If unset, or set to
0 it is disabled. It is intended as a resource to help avoid the OOM killer on
LINUX and manage resources in general. A backend request that would push the
total over the limit will be denied with an out of memory error causing that
backend's current query/transaction to fail. Due to the dynamic nature of memory
allocations, this limit is not exact. If within 1.5MB of the limit and two
backends request 1MB each at the same time both may be allocated, and exceed the
limit. Further requests will not be allocated until dropping below the limit.
Keep this in mind when setting this value. This limit does not affect auxiliary
backend processes. Backend memory allocations are displayed in the
pg_stat_activity view.
---
 doc/src/sgml/config.sgml                      |  26 +++++
 src/backend/storage/ipc/dsm_impl.c            |  12 ++
 src/backend/utils/activity/backend_status.c   | 107 ++++++++++++++++++
 src/backend/utils/misc/guc.c                  |  11 ++
 src/backend/utils/misc/postgresql.conf.sample |   3 +
 src/backend/utils/mmgr/aset.c                 |  17 +++
 src/backend/utils/mmgr/generation.c           |   9 ++
 src/backend/utils/mmgr/slab.c                 |   8 ++
 src/include/utils/backend_status.h            |   2 +
 9 files changed, 195 insertions(+)

index a5cd4e44c7..e70ea71ba1 100644
 
+     <varlistentry id="guc-max-total-backend-memory" xreflabel="max_total_backend_memory">
+      <term><varname>max_total_backend_memory</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>max_total_backend_memory</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies a limit to the amount of memory (MB) that may be allocated to
+        backends in total (i.e. this is not a per user or per backend limit).
+        If unset, or set to 0 it is disabled.  A backend request that would
+        push the total over the limit will be denied with an out of memory
+        error causing that backend's current query/transaction to fail. Due to
+        the dynamic nature of memory allocations, this limit is not exact. If
+        within 1.5MB of the limit and two backends request 1MB each at the same
+        time both may be allocated, and exceed the limit. Further requests will
+        not be allocated until dropping below the limit. Keep this in mind when
+        setting this value. This limit does not affect auxiliary backend
+        processes <xref linkend="glossary-auxiliary-proc"/> . Backend memory
+        allocations (<varname>backend_mem_allocated</varname>) are displayed in
+        the <link linkend="monitoring-pg-stat-activity-view"><structname>pg_stat_activity</structname></link>
+        view.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
      </sect2>
 
index 3356bb65b5..cc061056a3 100644

 
index 45da3af213..8ef9b0ffd5 100644

@@ -1253,3 +1255,108 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
+	/* Exclude auxiliary processes from the check */
+		ereport(WARNING,
+			 errmsg("request will exceed postgresql.conf defined max_total_backend_memory limit (%lu > %lu)",
+			 allocation_request, (uint64)max_total_bkend_mem * 1024 * 1024));
 
+	{
 
 # - Disk -

 

 

 
 			if (block == NULL)
index e0e69b394e..63c07120dd 100644

 		if (block == NULL)

 /* ----------

2.25.1

From 584a04f1b53948049e73165a4ffdd544c950ab0d Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

This new field displays the current bytes of memory allocated to the
backend process. It is updated as memory for the process is
malloc'd/free'd. Memory allocated to items on the freelist is included in
the displayed value.  Dynamic shared memory allocations are included
only in the value displayed for the backend that created them, they are
not included in the value for backends that are attached to them to
avoid double counting. On occasion, orphaned memory segments may be
cleaned up on postmaster startup. This may result in decreasing the sum
without a prior increment. We limit the floor of backend_mem_allocated
to zero. Updated pg_stat_activity documentation for the new column.
---
 doc/src/sgml/monitoring.sgml                |  12 +++
 src/backend/catalog/system_views.sql        |   1 +
 src/backend/storage/ipc/dsm_impl.c          |  80 +++++++++++++++
 src/backend/utils/activity/backend_status.c | 105 ++++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c         |   4 +-
 src/backend/utils/mmgr/aset.c               |  18 ++++
 src/backend/utils/mmgr/generation.c         |  15 +++
 src/backend/utils/mmgr/slab.c               |  21 ++++
 src/include/catalog/pg_proc.dat             |   6 +-
 src/include/utils/backend_status.h          |   7 +-
 src/test/regress/expected/rules.out         |   9 +-
 11 files changed, 269 insertions(+), 9 deletions(-)

+    <row>
index e1b90c5de4..3356bb65b5 100644
 
+		 * shown allocated in pg_stat_activity when the creator destroys the
+	 * allocated in pg_stat_activity for the creator process.
+		 * whole new size as input, growing the allocation as needed (only
+		 * truncate supports shrinking). We update by replacing the old
+		 * shown allocated in pg_stat_activity when the creator destroys the
+	 * allocated in pg_stat_activity for the creator process.

+		/*
+		 * shown allocated in pg_stat_activity when the creator destroys the
 
+	/*
+	 * allocated in pg_stat_activity for the creator process.
+		 * shown allocated in pg_stat_activity when the creator destroys the
+	 * allocated in pg_stat_activity for the creator process.
 
index c7ed1e6d7a..45da3af213 100644

 
+	/*
 
 	return activity;
 }
+
+/* --------
+	 * would have. There's no need for a lock around the read here as it's
+		ereport(LOG, errmsg("decrease reduces reported backend memory allocated below zero; setting reported to 0"));

 

 

 

 

 

 

 		block->aset = set;

 		block->aset = set;

 

 
 #include "lib/ilist.h"

 

 

 

 
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 2d70adef09..e0e69b394e 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
 
+	/*

 	Assert(slab);

 
+	 * Until header allocation is included in context->mem_allocated, cast to

 
 /* ----------
2.25.1

---

From: Reid Thompson <[email-masked]>
Date: Tue, 06 Sep 2022 20:17:25 -0400

> > budget is exhausted by DSM allocations. That doesn't seem

It's intended as a mechanism for administrators to limit total
postgresql memory consumption to avoid the OOM killer causing a crash
and restart, or to ensure that resources are available for other
processes on shared hosts, etc. It limits all types of allocations in
order to accomplish this.  Our documentation will note this, so that
administrators that have the need to set it are aware that it can
affect all non-auxiliary processes and what the effect is.

---

From: Reid Thompson <[email-masked]>
Date: Tue, 06 Sep 2022 20:25:06 -0400

On Fri, 2022-09-02 at 09:30 +0200, Drouvot, Bertrand wrote:
> Hi,
> 
> I'm not sure we are choosing the right victims here (aka the ones
> that are doing the request that will push the total over the limit).
>
> Imagine an extreme case where a single backend consumes say 99% of
> the limit, shouldn't it be the one to be "punished"? (and somehow forced
> to give the memory back).
> 
> The problem that i see with the current approach is that a "bad"
> backend could impact all the others and continue to do so.
> 
> what about punishing say the highest consumer , what do you think?
> (just speaking about the general idea here, not about the implementation)

Initially, we believe that punishing the detector is reasonable if we
can help administrators avoid the OOM killer/resource starvation.  But
we can and should expand on this idea.

Another thought is, rather than just failing the query/transaction we
have the affected backend do a clean exit, freeing all it's resources.

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

---

From: Stephen Frost <[email-masked]>
Date: Fri, 9 Sep 2022 12:48:56 -0400

Greetings,

> by cache entries when there's memory pressure?

Short answer to this is yes, and that's an issue, but it isn't this
patch's problem to deal with- that's an issue that the relcache system
needs to be changed to address.

> might make it quite infuriating for anyone trying to do something

Agreed that this could happen but I don't imagine it to be super likely-
and even if it does, this is probably a better position to be in as the
backend could then be disconnected from and would then go away and its
memory free'd, unlike the current OOM-killer situation where we crash
and go through recovery.  We should note this in the documentation
though, sure, so that administrators understand how this can occur and
can take action to address it.

> hazard that the deadlock detector would need to be made aware of.

Sure, that also sounds great and a query acceptance system would be
wonderful.  If someone is working on that with an expectation of it
landing before v16, great.  Otherwise, I don't see it as relevant to
the question about if we should include this feature or not, and I'm not
even sure that we'd refuse this feature even if we already had an
acceptance system as a stop-gap should we guess wrong and not realize it
until it's too late.

Thanks,

Stephen

---

From: Justin Pryzby <[email-masked]>
Date: Fri, 9 Sep 2022 12:14:17 -0500

> Is this noting that we'd set a ceiling of 2048MB?

The reason is that you're later multiplying it by 1024*1024, so you need
to limit it to avoid overflowing.  Compare with
min_dynamic_shared_memory, Log_RotationSize, maintenance_work_mem,
autovacuum_work_mem.

typo: Explicitely

I wouldn't mention postgresql.conf - it could be in
postgresql.auto.conf, or an include file, or a -c parameter.
Suggest: allocation would exceed max_total_backend_memory limit...

Suggest: deallocation would decrease backend memory below zero;

Should this be PGC_SU_BACKEND to allow a superuser to set a higher
limit (or no limit)?

There's compilation warning under mingw cross compile due to
sizeof(long).  See d914eb347 and other recent commits which I guess is
the current way to handle this.
http://cfbot.cputube.org/reid-thompson.html

For performance test, you'd want to check what happens with a large
number of max_connections (and maybe a large number of clients).  TPS
isn't the only thing that matters.  For example, a utility command might
sometimes do a lot of allocations (or deallocations), or a
"parameterized nested loop" may loop over over many outer tuples and
reset for each.  There's also a lot of places that reset to a
"per-tuple" context.  I started looking at its performance, but nothing
to show yet.

Would you keep people copied on your replies ("reply all") ?  Otherwise
I (at least) may miss them.  I think that's what's typical on these
lists (and the list tool is smart enough not to send duplicates to
people who are direct recipients).

-- 
Justin

---

From: Reid Thompson <[email-masked]>
Date: Mon, 12 Sep 2022 12:25:25 -0400

> min_dynamic_shared_memory, Log_RotationSize, maintenance_work_mem,

What I originally attempted to implement is:
GUC "max_total_backend_memory" max value as INT_MAX = 2147483647 MB
(2251799812636672 bytes). And the other variables and comparisons as
bytes represented as uint64 to avoid overflow.

Is this invalid?

> typo: Explicitely

corrected

> +                        errmsg("request will exceed postgresql.conf
> defined max_total_backend_memory limit (%lu > %lu)",
> 

updated

> 
> +               ereport(LOG, errmsg("decrease reduces reported
> backend memory allocated below zero; setting reported to 0"));
> 

updated

> Should this be PGC_SU_BACKEND to allow a superuser to set a higher

Sounds good to me. I'll update to that.
Would PGC_SUSET be too open?

> http://cfbot.cputube.org/reid-thompson.html

updated %lu to %llu and changed cast from uint64 to 
unsigned long long in the ereport call

> "per-tuple" context.  I started looking at its performance, but

Thanks

> people who are direct recipients).

Ok - will do, thanks.

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

 
+    <row>

 
+		/*
 
+	/*

 
 
+	/*
 
 	return activity;
 }
+
+/* --------

 

 

 

 

 

 

 		block->aset = set;

 		block->aset = set;

 

 
 #include "lib/ilist.h"

 

 

 

 
 
 #include "lib/ilist.h"
 
+	/*

 	Assert(slab);

 

 
 /* ----------

From 23d33838e3780ef02daad2bc737290d9905745a7 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Sat, 4 Jun 2022 22:23:59 -0400
Subject: [PATCH 2/2] Add the ability to limit the amount of memory that can be
 allocated to backends.

Specifies a limit to the amount of memory (in MB) that may be allocated to
backends in total (i.e. this is not a per user or per backend limit). If unset,
or set to 0 it is disabled. It is intended as a resource to help avoid the OOM
killer on LINUX and manage resources in general. A backend request that would
push the total over the limit will be denied with an out of memory error causing
that backend's current query/transaction to fail. Due to the dynamic nature of
memory allocations, this limit is not exact. If within 1.5MB of the limit and
two backends request 1MB each at the same time both may be allocated, and exceed
the limit. Further requests will not be allocated until dropping below the
limit. Keep this in mind when setting this value. This limit does not affect
auxiliary backend processes. Backend memory allocations are displayed in the
pg_stat_activity view.
---
 doc/src/sgml/config.sgml                      |  26 +++++
 src/backend/storage/ipc/dsm_impl.c            |  12 ++
 src/backend/utils/activity/backend_status.c   | 109 +++++++++++++++++-
 src/backend/utils/misc/guc.c                  |  11 ++
 src/backend/utils/misc/postgresql.conf.sample |   3 +
 src/backend/utils/mmgr/aset.c                 |  17 +++
 src/backend/utils/mmgr/generation.c           |   9 ++
 src/backend/utils/mmgr/slab.c                 |   8 ++
 src/include/utils/backend_status.h            |   2 +
 9 files changed, 196 insertions(+), 1 deletion(-)

 

 
index 45da3af213..9c2fc2f07c 100644

 /* exposed so that backend_progress.c can access it */
@@ -1235,7 +1237,7 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
 	 */
 	if (deallocation > beentry->backend_mem_allocated)
 	{
-		ereport(LOG, errmsg("decrease reduces reported backend memory allocated below zero; setting reported to 0"));
+		ereport(LOG, errmsg("deallocation would decrease backend memory below zero; setting reported to 0"));
 
 		/*
 		 * Overwrite deallocation with current backend_mem_allocated so we end
+		 * Explicitly identify the OOM being a result of this configuration
+		 * parameter vs a system failure to allocate OOM.
+			 errmsg("allocation would exceed max_total_backend_memory limit (%llu > %llu)",
+			 (unsigned long long)pgstat_get_all_backend_memory_allocated() +
+			 allocation_request, (unsigned long long)max_total_bkend_mem * 1024 * 1024));
index 9fbbfb1be5..4e256a77d5 100644
 
+	{
+		{"max_total_backend_memory", PGC_SU_BACKEND, RESOURCES_MEM,
 
 # - Disk -

 

 

 
 			if (block == NULL)

 		if (block == NULL)

 /* ----------

---

From: Ibrar Ahmed <[email-masked]>
Date: Thu, 15 Sep 2022 12:07:25 +0400

On Mon, Sep 12, 2022 at 8:30 PM Reid Thompson <[email-masked]>
wrote:

> The patch does not apply; please rebase the patch.

patching file src/backend/utils/misc/guc.c
Hunk #1 FAILED at 3664.
1 out of 1 hunk FAILED -- saving rejects to file
src/backend/utils/misc/guc.c.rej

patching file src/backend/utils/misc/postgresql.conf.sample

-- 
Ibrar Ahmed

---

From: Reid Thompson <[email-masked]>
Date: Thu, 15 Sep 2022 10:58:19 -0400

> patching file src/backend/utils/misc/postgresql.conf.sample

rebased patches attached.

Thanks,
Reid

From 0e7010c53508d5a396edd16fd9166abe431f5dbe Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

 
+    <row>
index 55f7ec79e0..a78750ab12 100644
@@ -862,6 +862,7 @@ CREATE VIEW pg_stat_activity AS

 
+		/*
 
+	/*

 
 
+	/*
 
 	return activity;
 }
+
+/* --------
index be15b4b2e5..35d497a12e 100644
 
index ec423375ae..2ac6f10e12 100644

 

 

 

 

 

 	/* Finally, free the context header, including the keeper block */
 	free(set);
@@ -718,6 +731,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;

 		block->aset = set;
 		block->freeptr = block->endptr = ((char *) block) + blksize;
@@ -928,6 +942,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;

 		block->aset = set;
 		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -1028,6 +1043,7 @@ AllocSetFree(void *pointer)
 			block->next->prev = block->prev;

 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -1144,7 +1160,9 @@ AllocSetRealloc(void *pointer, Size size)

 
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index c743b24fa7..34b11392ff 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"

 

 
@@ -363,6 +374,7 @@ GenerationAlloc(MemoryContext context, Size size)
 			return NULL;

 		/* block with a single (used) chunk */
 		block->context = set;
@@ -466,6 +478,7 @@ GenerationAlloc(MemoryContext context, Size size)
 				return NULL;

 			/* initialize the new block */
 			GenerationBlockInit(set, block, blksize);
@@ -699,6 +712,8 @@ GenerationFree(void *pointer)
 	dlist_delete(&block->node);

diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 9149aaafcb..72376da82e 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
@@ -223,6 +224,12 @@ SlabContextCreate(MemoryContext parent,
 						parent,
 						name);
 
+	/*
 
@@ -238,6 +245,7 @@ SlabReset(MemoryContext context)
 {
 	int			i;
 	SlabContext *slab = castNode(SlabContext, context);
+	uint64		deallocation = 0;
 
 	Assert(slab);
 
@@ -263,9 +271,11 @@ SlabReset(MemoryContext context)
 			free(block);
 			slab->nblocks--;
 			context->mem_allocated -= slab->blockSize;
+			deallocation += slab->blockSize;
 		}
 	}

@@ -279,8 +289,17 @@ SlabReset(MemoryContext context)
@@ -349,6 +368,7 @@ SlabAlloc(MemoryContext context, Size size)
 
@@ -514,6 +534,7 @@ SlabFree(void *pointer)
index a07e737a33..363d92e9f2 100644

 
 /* ----------
index 9dd137415e..4588d71c8a 100644
@@ -1752,9 +1752,10 @@ pg_stat_activity| SELECT s.datid,
@@ -1866,7 +1867,7 @@ pg_stat_gssapi| SELECT s.pid,
@@ -2047,7 +2048,7 @@ pg_stat_replication| SELECT s.pid,
@@ -2081,7 +2082,7 @@ pg_stat_ssl| SELECT s.pid,

From bb8e1a2bbb9425eb7667a97dc49beebe8f9bf327 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Sat, 4 Jun 2022 22:23:59 -0400
Subject: [PATCH 2/2] Add the ability to limit the amount of memory that can be
 allocated to backends.

Specifies a limit to the amount of memory (in MB) that may be allocated to
backends in total (i.e. this is not a per user or per backend limit). If unset,
or set to 0 it is disabled. It is intended as a resource to help avoid the OOM
killer on LINUX and manage resources in general. A backend request that would
push the total over the limit will be denied with an out of memory error causing
that backend's current query/transaction to fail. Due to the dynamic nature of
memory allocations, this limit is not exact. If within 1.5MB of the limit and
two backends request 1MB each at the same time both may be allocated, and exceed
the limit. Further requests will not be allocated until dropping below the
limit. Keep this in mind when setting this value. This limit does not affect
auxiliary backend processes. Backend memory allocations are displayed in the
pg_stat_activity view.
---
 doc/src/sgml/config.sgml                      |  26 ++++
 src/backend/storage/ipc/dsm_impl.c            |  12 ++
 src/backend/utils/activity/backend_status.c   | 111 +++++++++++++++++-
 src/backend/utils/misc/guc_tables.c           |  11 ++
 src/backend/utils/misc/postgresql.conf.sample |   3 +
 src/backend/utils/mmgr/aset.c                 |  17 +++
 src/backend/utils/mmgr/generation.c           |  11 +-
 src/backend/utils/mmgr/slab.c                 |   8 ++
 src/include/utils/backend_status.h            |   2 +
 9 files changed, 199 insertions(+), 2 deletions(-)

index 700914684d..ce8e35daee 100644

 

index 45da3af213..7820c55489 100644
@@ -45,6 +45,9 @@

@@ -1235,7 +1238,7 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
 
 		/*
 		 * Overwrite deallocation with current backend_mem_allocated so we end
@@ -1253,3 +1256,109 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
 	beentry->backend_mem_allocated -= deallocation;
 	PGSTAT_END_WRITE_ACTIVITY(beentry);
 }
+
+/* ----------
+ * pgstat_get_all_backend_memory_allocated() -
+ *
+ *	Return a uint64 representing the current shared memory allocated to all
+ *	backends.  This looks directly at the BackendStatusArray, and so will
+ *	provide current information regardless of the age of our transaction's
+ *	snapshot of the status array.
+ *	In the future we will likely utilize additional values - perhaps limit
+ *	backend allocation by user/role, etc.
+ * ----------
+ */
+uint64
+pgstat_get_all_backend_memory_allocated(void)
+{
+	PgBackendStatus *beentry;
+	int			i;
+	uint64		all_backend_memory_allocated = 0;
+
+	beentry = BackendStatusArray;
+
+	/*
+	 * We probably shouldn't get here before shared memory has been set up,
+	 * but be safe.
+	 */
+	if (beentry == NULL || BackendActivityBuffer == NULL)
+		return 0;
+
+	/*
+	 * We include AUX procs in all backend memory calculation
+	 */
+	for (i = 1; i <= NumBackendStatSlots; i++)
+	{
+		/*
+		 * We use a volatile pointer here to ensure the compiler doesn't try
+		 * to get cute.
+		 */
+		volatile PgBackendStatus *vbeentry = beentry;
+		bool		found;
+		uint64		backend_mem_allocated = 0;
+
+		for (;;)
+		{
+			int			before_changecount;
+			int			after_changecount;
+
+			pgstat_begin_read_activity(vbeentry, before_changecount);
+
+			/*
+			 * Ignore invalid entries, which may contain invalid data.
+			 * See pgstat_beshutdown_hook()
+			 */
+			if (vbeentry->st_procpid > 0)
+				backend_mem_allocated = vbeentry->backend_mem_allocated;
+
+			pgstat_end_read_activity(vbeentry, after_changecount);
+
+			if ((found = pgstat_read_activity_complete(before_changecount,
+													   after_changecount)))
+				break;
+
+			/* Make sure we can break out of loop if stuck... */
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		if (found)
+			all_backend_memory_allocated += backend_mem_allocated;
+
+		beentry++;
+	}
+
+	return all_backend_memory_allocated;
+}
+
+/*
+ * Determine if allocation request will exceed max backend memory allowed.
+ * Do not apply to auxiliary processes.
+ */
+bool
+exceeds_max_total_bkend_mem(uint64 allocation_request)
+{
+	bool		result = false;
+
+	/* Exclude auxiliary processes from the check */
+	if (MyAuxProcType != NotAnAuxProcess)
+		return result;
+
+	/* Convert max_total_bkend_mem to bytes for comparison */
+	if (max_total_bkend_mem &&
+		pgstat_get_all_backend_memory_allocated() +
+		allocation_request > (uint64) max_total_bkend_mem * 1024 * 1024)
+	{
+		/*
+		 * Explicitly identify the OOM being a result of this configuration
+		 * parameter vs a system failure to allocate OOM.
+		 */
+		ereport(WARNING,
+				errmsg("allocation would exceed max_total_backend_memory limit (%llu > %llu)",
+					   (unsigned long long) pgstat_get_all_backend_memory_allocated() +
+					   allocation_request, (unsigned long long) max_total_bkend_mem * 1024 * 1024));
+
+		result = true;
+	}
+
+	return result;
+}
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 550e95056c..7d4dc8677a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3415,6 +3415,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
index 2ae76e5cfb..8a0b383eb7 100644
 
 # - Disk -
 
index 2ac6f10e12..509b93faa1 100644
 
@@ -726,6 +730,11 @@ AllocSetAlloc(MemoryContext context, Size size)
 #endif
 
@@ -923,6 +932,10 @@ AllocSetAlloc(MemoryContext context, Size size)

@@ -1150,6 +1163,10 @@ AllocSetRealloc(void *pointer, Size size)
 		blksize = chksize + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
 		oldblksize = block->endptr - ((char *) block);
 
index 34b11392ff..6256e84d48 100644
 
+	if (exceeds_max_total_bkend_mem(allocSize))
+		return NULL;
+
 	/*
 	 * Allocate the initial block.  Unlike other generation.c blocks, it
 	 * starts with the context header and its block header follows that.
@@ -276,7 +279,7 @@ GenerationReset(MemoryContext context)
 {
 	GenerationContext *set = (GenerationContext *) context;
 	dlist_mutable_iter miter;
-	uint64	deallocation = 0;
+	uint64		deallocation = 0;

@@ -369,6 +372,9 @@ GenerationAlloc(MemoryContext context, Size size)
 	{
 		Size		blksize = required_size + Generation_BLOCKHDRSZ;
 
@@ -472,6 +478,9 @@ GenerationAlloc(MemoryContext context, Size size)

 			if (block == NULL)
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 72376da82e..364c9eb795 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -182,6 +182,10 @@ SlabContextCreate(MemoryContext parent,
 	headerSize += chunksPerBlock * sizeof(bool);
 #endif
 
@@ -336,6 +340,10 @@ SlabAlloc(MemoryContext context, Size size)
 
 		if (block == NULL)

 /* ----------

---

From: Arne Roland <[email-masked]>
Date: Mon, 24 Oct 2022 15:27:51 +0000

Hello Reid,

could you rebase the patch again? It doesn't apply currently (http://cfbot.cputube.org/patch_40_3867.log). Thanks!

You mention, that you want to prevent the compiler from getting cute.

I don't think this comments are exactly helpful in the current state. I think probably fine to just omit them.

I don't understand the purpose of the result variable in exceeds_max_total_bkend_mem. What purpose does it serve?

I really like the simplicity of the suggestion here to prevent oom.

I intent to play around with a lot of backends, once I get a rebased patch.

Regards

Arne

________________________________
From: Reid Thompson <[email-masked]>
Sent: Thursday, September 15, 2022 4:58:19 PM
To: Ibrar Ahmed; [email-masked]
Cc: [email-masked]; Justin Pryzby
Subject: Re: Add the ability to limit the amount of memory that can be allocated to backends.

Thanks,
Reid

---

From: Reid Thompson <[email-masked]>
Date: Tue, 25 Oct 2022 11:49:03 -0400

Hi Arne,

On Mon, 2022-10-24 at 15:27 +0000, Arne Roland wrote:
> Hello Reid,
> 
> could you rebase the patch again? It doesn't apply currently
> (http://cfbot.cputube.org/patch_40_3867.log). Thanks!

> You mention, that you want to prevent the compiler from getting
> cute.I don't think this comments are exactly helpful in the current
> state. I think probably fine to just omit them.

I attempted to follow previous convention when adding code and these
comments have been consistently applied throughout backend_status.c
where a volatile pointer is being used.

> I don't understand the purpose of the result variable in
> exceeds_max_total_bkend_mem. What purpose does it serve?
> 

If max_total_backend_memory is configured, exceeds_max_total_bkend_mem()
will return true if an allocation request will push total backend memory
allocated over the configured value.

exceeds_max_total_bkend_mem() is implemented in the various allocators
along the lines of
...snip...
        /* Do not exceed maximum allowed memory allocation */
        if (exceeds_max_total_bkend_mem('new request size'))                                                                                   
            return NULL;                                                                                                            
...snip...
Do not allocate the memory requested, return NULL instead. PG already
had code in place to handle NULL returns from allocation requests.

The allocation code in aset.c, slab.c, generation.c, dsm_impl.c utilizes
 exceeds_max_total_bkend_mem()

max_total_backend_memory (integer)
Specifies a limit to the amount of memory (MB) that may be allocated
to backends in total (i.e. this is not a per user or per backend limit).
If unset, or set to 0 it is disabled. A backend request that would push
the total over the limit will be denied with an out of memory error
causing that backend's current query/transaction to fail. Due to the
dynamic nature of memory allocations, this limit is not exact. If within
1.5MB of the limit and two backends request 1MB each at the same time
both may be allocated, and exceed the limit. Further requests will not
be allocated until dropping below the limit. Keep this in mind when
setting this value. This limit does not affect auxiliary backend
processes Auxiliary process . Backend memory allocations
(backend_mem_allocated) are displayed in the pg_stat_activity view.

> I intent to play around with a lot of backends, once I get a rebased

From ab654a48ec7bfbc3bc377c5757a04f1756e72e79 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

index e5d622d514..4983bbc814 100644
 
+    <row>
index 2d8104b090..cbf804625c 100644
@@ -865,6 +865,7 @@ CREATE VIEW pg_stat_activity AS

 
+		/*
 
+	/*
 
index 1146a6c33c..5c33824eb8 100644

 
+	/*
@@ -1191,3 +1200,99 @@ pgstat_clip_activity(const char *raw_activity)
 
 	return activity;
 }
+
+/* --------
index 96bffc0f2a..692ed1df18 100644
@@ -553,7 +553,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
@@ -609,6 +609,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[16] = true;
 
index db402e3a41..f6d1333f3d 100644
 
@@ -521,6 +522,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 						name);

 	return (MemoryContext) set;
 }
@@ -543,6 +545,7 @@ AllocSetReset(MemoryContext context)
 	AllocSet	set = (AllocSet) context;
 	AllocBlock	block;
 	Size		keepersize PG_USED_FOR_ASSERTS_ONLY;
+	uint64		deallocation = 0;

@@ -585,6 +588,7 @@ AllocSetReset(MemoryContext context)
 		{
 			/* Normal case, release the block */
 			context->mem_allocated -= block->endptr - ((char *) block);
+			deallocation += block->endptr - ((char *) block);
 
 #ifdef CLOBBER_FREED_MEMORY
 			wipe_mem(block, block->freeptr - ((char *) block));
@@ -595,6 +599,7 @@ AllocSetReset(MemoryContext context)
 	}

 	/* Reset block size allocation sequence, too */
 	set->nextBlockSize = set->initBlockSize;
@@ -613,6 +618,7 @@ AllocSetDelete(MemoryContext context)
 	AllocSet	set = (AllocSet) context;
 	AllocBlock	block = set->blocks;
 	Size		keepersize PG_USED_FOR_ASSERTS_ONLY;
+	uint64		deallocation = 0;

@@ -651,11 +657,13 @@ AllocSetDelete(MemoryContext context)

 
 		/* Now add the just-deleted context to the freelist. */
@@ -672,7 +680,10 @@ AllocSetDelete(MemoryContext context)
 		AllocBlock	next = block->next;

 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -685,6 +696,8 @@ AllocSetDelete(MemoryContext context)
 	}

 	/* Finally, free the context header, including the keeper block */
 	free(set);
@@ -734,6 +747,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;

 		block->aset = set;
 		block->freeptr = block->endptr = ((char *) block) + blksize;
@@ -944,6 +958,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;

 		block->aset = set;
 		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -1043,6 +1058,7 @@ AllocSetFree(void *pointer)
 			block->next->prev = block->prev;

 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -1173,7 +1189,9 @@ AllocSetRealloc(void *pointer, Size size)

 
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index 4cb75f493f..7bb9175f6d 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"
@@ -267,6 +268,7 @@ GenerationContextCreate(MemoryContext parent,
 						name);

@@ -283,6 +285,7 @@ GenerationReset(MemoryContext context)

@@ -305,9 +308,14 @@ GenerationReset(MemoryContext context)

@@ -328,6 +336,9 @@ GenerationDelete(MemoryContext context)
 {
 	/* Reset to release all releasable GenerationBlocks */
 	GenerationReset(context);
+
+	pgstat_report_backend_mem_allocated_decrease(context->mem_allocated);
+
 	/* And free the context header and keeper block */
 	free(context);
 }
@@ -374,6 +385,7 @@ GenerationAlloc(MemoryContext context, Size size)
 			return NULL;

 		/* block with a single (used) chunk */
 		block->context = set;
@@ -477,6 +489,7 @@ GenerationAlloc(MemoryContext context, Size size)
 				return NULL;

 			/* initialize the new block */
 			GenerationBlockInit(set, block, blksize);
@@ -726,6 +739,8 @@ GenerationFree(void *pointer)
 	dlist_delete(&block->node);

diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 1a0b28f9ea..efdc2736c1 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
@@ -238,6 +239,12 @@ SlabContextCreate(MemoryContext parent,
 						parent,
 						name);
 
+	/*
 
@@ -253,6 +260,7 @@ SlabReset(MemoryContext context)
 {
 	SlabContext *slab = (SlabContext *) context;
 	int			i;
+	uint64		deallocation = 0;
 
 	AssertArg(SlabIsValid(slab));
 
@@ -278,9 +286,11 @@ SlabReset(MemoryContext context)
 			free(block);
 			slab->nblocks--;
 			context->mem_allocated -= slab->blockSize;
+			deallocation += slab->blockSize;
 		}
 	}

@@ -294,8 +304,17 @@ SlabReset(MemoryContext context)
@@ -364,6 +383,7 @@ SlabAlloc(MemoryContext context, Size size)
 
@@ -537,6 +557,7 @@ SlabFree(void *pointer)
index 62a5b8e655..737a7c5034 100644
@@ -5347,9 +5347,9 @@
index b582b46e9f..d59a1d50f6 100644
@@ -169,6 +169,9 @@ typedef struct PgBackendStatus

@@ -313,7 +316,9 @@ extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
 
 /* ----------
index bfcd8ac9a0..36947c636d 100644
@@ -1869,7 +1870,7 @@ pg_stat_gssapi| SELECT s.pid,
@@ -2050,7 +2051,7 @@ pg_stat_replication| SELECT s.pid,
@@ -2084,7 +2085,7 @@ pg_stat_ssl| SELECT s.pid,

From 7c6735a34d22fde1a5103bd962d0a45f1322e87d Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Sat, 4 Jun 2022 22:23:59 -0400
Subject: [PATCH 2/2] Add the ability to limit the amount of memory that can be
 allocated to backends.

index 559eb898a9..4d22491a7e 100644

 

index 5c33824eb8..872fe66188 100644

@@ -1278,7 +1281,7 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
 
 		/*
@@ -1296,3 +1299,109 @@ pgstat_report_backend_mem_allocated_decrease(uint64 deallocation)
index 05ab087934..745cc2ca9c 100644
@@ -3405,6 +3405,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
index 868d21c351..1ce0dee6d0 100644
 
 # - Disk -
 
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index f6d1333f3d..5c659dc0fc 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -440,6 +440,10 @@ AllocSetContextCreateInternal(MemoryContext parent,
 	else
 		firstBlockSize = Max(firstBlockSize, initBlockSize);
 
@@ -742,6 +746,11 @@ AllocSetAlloc(MemoryContext context, Size size)
 #endif
 
@@ -939,6 +948,10 @@ AllocSetAlloc(MemoryContext context, Size size)

@@ -1179,6 +1192,10 @@ AllocSetRealloc(void *pointer, Size size)
 		blksize = chksize + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
 		oldblksize = block->endptr - ((char *) block);
 
+		/* Do not exceed maximum allowed memory allocation */
+		if (blksize > oldblksize && exceeds_max_total_bkend_mem(blksize - oldblksize))
+			return NULL;
+
 		block = (AllocBlock) realloc(block, blksize);
 		if (block == NULL)
 		{
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index 7bb9175f6d..ef2e11aefc 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -201,6 +201,9 @@ GenerationContextCreate(MemoryContext parent,
 	else
 		allocSize = Max(allocSize, initBlockSize);
 
@@ -285,7 +288,7 @@ GenerationReset(MemoryContext context)

@@ -380,6 +383,9 @@ GenerationAlloc(MemoryContext context, Size size)
 	{
 		Size		blksize = required_size + Generation_BLOCKHDRSZ;
 
@@ -483,6 +489,9 @@ GenerationAlloc(MemoryContext context, Size size)

 			if (block == NULL)
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index efdc2736c1..6ec512defd 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -197,6 +197,10 @@ SlabContextCreate(MemoryContext parent,
 	headerSize += chunksPerBlock * sizeof(bool);
 #endif
 
@@ -351,6 +355,10 @@ SlabAlloc(MemoryContext context, Size size)
 
 		if (block == NULL)
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index d59a1d50f6..0403a24eef 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -278,6 +278,7 @@ typedef struct LocalPgBackendStatus
  */
 extern PGDLLIMPORT bool pgstat_track_activities;
 extern PGDLLIMPORT int pgstat_track_activity_query_size;
+extern PGDLLIMPORT int max_total_bkend_mem;

 /* ----------
@@ -329,6 +330,7 @@ extern int	pgstat_fetch_stat_numbackends(void);
 extern PgBackendStatus *pgstat_fetch_stat_beentry(BackendId beid);
 extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 extern char *pgstat_clip_activity(const char *raw_activity);
+extern bool exceeds_max_total_bkend_mem(uint64 allocation_request);

---

From: Reid Thompson <[email-masked]>
Date: Thu, 03 Nov 2022 11:48:50 -0400

> rebased patches attached.

Rebased to current. Add a couple changes per conversation with D
Christensen (include units in field name, group field with backend_xid
and backend_xmin fields in pg_stat_activity view, rather than between
query_id and query)

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

From 9cf35c79be107feedb63f6f674ac9d2347d1875e Mon Sep 17 00:00:00 2001

 9 files changed, 198 insertions(+), 1 deletion(-)

index 559eb898a9..5762999fa5 100644
 
+        allocations (<varname>backend_allocated_bytes</varname>) are displayed in
 
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index eae03159c3..aaf74e9486 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -254,6 +254,10 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 		return true;
 	}
 
@@ -525,6 +529,10 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 
@@ -719,6 +727,10 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 		return true;
 	}
 
index 30a89e899a..5500ed4f37 100644

 /* exposed so that backend_progress.c can access it */
 PgBackendStatus *MyBEEntry = NULL;
@@ -1278,7 +1281,7 @@ pgstat_report_backend_allocated_bytes_decrease(uint64 deallocation)
 	 */
 	if (deallocation > beentry->backend_allocated_bytes)
 	{
-		ereport(LOG, errmsg("decrease reduces reported backend memory allocated below zero; setting reported to 0"));
+		ereport(LOG, errmsg("deallocation would decrease backend memory below zero; setting reported to 0"));
 
 		/*
 		 * Overwrite deallocation with current backend_allocated_bytes so we
@@ -1296,3 +1299,109 @@ pgstat_report_backend_allocated_bytes_decrease(uint64 deallocation)
 	beentry->backend_allocated_bytes -= deallocation;
+		uint64		backend_allocated_bytes = 0;
+				backend_allocated_bytes = vbeentry->backend_allocated_bytes;
+			all_backend_memory_allocated += backend_allocated_bytes;
index 836b49484a..0e09766949 100644
@@ -3403,6 +3403,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
 
 # - Disk -
 
index 81e62e4981..cc865a89e0 100644

 

index df3007edfb..495665d3b0 100644

 
 
 			if (block == NULL)
index 532c038973..5b98176654 100644

 		if (block == NULL)
index 75d87e8308..c8beb116b8 100644

 /* ----------

From 8f729c59c3aa1a02d008795159a748e1592a9916 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

 src/backend/storage/ipc/dsm_impl.c          |  81 +++++++++++++++
 11 files changed, 270 insertions(+), 9 deletions(-)

index e5d622d514..972805b85a 100644
 
+    <row>
+     <entry role="catalog_table_entry"><para role="column_definition">
+      <structfield>backend_allocated_bytes</structfield> <type>bigint</type>
+     </para>
+     <para>
+      The byte count of memory allocated to this backend. Dynamic shared memory
+      allocations are included only in the value displayed for the backend that
+      created them, they are not included in the value for backends that are
+      attached to them to avoid double counting.
+     </para></entry>
+    </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>query</structfield> <type>text</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 2d8104b090..84d462aa97 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -864,6 +864,7 @@ CREATE VIEW pg_stat_activity AS
             S.state,
             S.backend_xid,
             s.backend_xmin,
+            S.backend_allocated_bytes,
             S.query_id,
             S.query,
             S.backend_type
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 6ddd46a4e7..eae03159c3 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -66,6 +66,7 @@
 #include "postmaster/postmaster.h"
 #include "storage/dsm_impl.h"
 #include "storage/fd.h"
+#include "utils/backend_status.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 
@@ -232,6 +233,14 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && shm_unlink(name) != 0)
@@ -332,6 +341,36 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+	{
+		/*
+		 * Posix creation calls dsm_impl_posix_resize implying that resizing
+		 * occurs or may be added in the future. As implemented
+		 * dsm_impl_posix_resize utilizes fallocate or truncate, passing the
+		 * whole new size as input, growing the allocation as needed (only
+		 * truncate supports shrinking). We update by replacing the old
+		 * allocation with the new.
+		 */
+#if defined(HAVE_POSIX_FALLOCATE) && defined(__linux__)
+		/*
+		 * posix_fallocate does not shrink allocations, adjust only on
+		 * allocation increase.
+		 */
+		if (request_size > *mapped_size)
+		{
+			pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
+			pgstat_report_backend_allocated_bytes_increase(request_size);
+		}
+#else
+		pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
+		pgstat_report_backend_allocated_bytes_increase(request_size);
+#endif
+	}
 	*mapped_address = address;
 	*mapped_size = request_size;
 	close(fd);
@@ -537,6 +576,14 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && shmctl(ident, IPC_RMID, NULL) < 0)
@@ -584,6 +631,13 @@ dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_allocated_bytes_increase(request_size);
 	*mapped_address = address;
 	*mapped_size = request_size;
 
@@ -652,6 +706,13 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 			return false;
 		}
 
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		if (op == DSM_OP_DESTROY)
+			pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
 		*impl_private = NULL;
 		*mapped_address = NULL;
 		*mapped_size = 0;
@@ -768,6 +829,12 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 		return false;
 	}
 
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_allocated_bytes_increase(info.RegionSize);
 	*mapped_address = address;
 	*mapped_size = info.RegionSize;
 	*impl_private = hmap;
@@ -812,6 +879,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		pgstat_report_backend_allocated_bytes_decrease(*mapped_size);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && unlink(name) != 0)
@@ -933,6 +1007,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_backend_allocated_bytes_increase(request_size);
 	*mapped_address = address;
 	*mapped_size = request_size;
 
index 1146a6c33c..30a89e899a 100644
 
+/* Memory allocated to this backend prior to pgstats initialization */
+uint64		backend_allocated_bytes = 0;

+	/*
+	 * Move sum of memory allocated prior to pgstats initialization to pgstats
+	 * and zero the local variable.
+	 */
+	lbeentry.backend_allocated_bytes = backend_allocated_bytes;
+	backend_allocated_bytes = 0;
+
 	/*
 	 * we don't zero st_progress_param here to save cycles; nobody should
 	 * examine it until st_progress_command has been set to something other
@@ -1191,3 +1200,99 @@ pgstat_clip_activity(const char *raw_activity)
 
 	return activity;
 }
+
+/* --------
+ * pgstat_report_backend_allocated_bytes_increase() -
+ *
+ * Called to report increase in memory allocated for this backend
+ * --------
+ */
+void
+pgstat_report_backend_allocated_bytes_increase(uint64 allocation)
+{
+	volatile PgBackendStatus *beentry = MyBEEntry;
+
+	if (!beentry || !pgstat_track_activities)
+	{
+		/*
+		 * Account for memory before pgstats is initialized. This will be
+		 * migrated to pgstats on initialization.
+		 */
+		backend_allocated_bytes += allocation;
+
+		return;
+	}
+
+	/*
+	 * Update my status entry, following the protocol of bumping
+	 * st_changecount before and after.  We use a volatile pointer here to
+	 * ensure the compiler doesn't try to get cute.
+	 */
+	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
+	beentry->backend_allocated_bytes += allocation;
+	PGSTAT_END_WRITE_ACTIVITY(beentry);
+}
+
+/* --------
+ * pgstat_report_backend_allocated_bytes_decrease() -
+ *
+ * Called to report decrease in memory allocated for this backend
+ * --------
+ */
+void
+pgstat_report_backend_allocated_bytes_decrease(uint64 deallocation)
+{
+	volatile PgBackendStatus *beentry = MyBEEntry;
+
+	/*
+	 * Cases may occur where shared memory from a previous postmaster
+	 * invocation still exist. These are cleaned up at startup by
+	 * dsm_cleanup_using_control_segment. Limit decreasing memory allocated to
+	 * zero in case no corresponding prior increase exists or decrease has
+	 * already been accounted for.
+	 */
+
+	if (!beentry || !pgstat_track_activities)
+	{
+		/*
+		 * Account for memory before pgstats is initialized. This will be
+		 * migrated to pgstats on initialization. Do not allow
+		 * backend_allocated_bytes to go below zero. If pgstats has not been
+		 * initialized, we are in startup and we set backend_allocated_bytes
+		 * to zero in cases where it would go negative and skip generating an
+		 * ereport.
+		 */
+		if (deallocation > backend_allocated_bytes)
+			backend_allocated_bytes = 0;
+		else
+			backend_allocated_bytes -= deallocation;
+
+		return;
+	}
+
+	/*
+	 * Do not allow backend_allocated_bytes to go below zero. ereport if we
+	 * would have. There's no need for a lock around the read here as it's
+	 * being referenced from the same backend which means that there shouldn't
+	 * be concurrent writes. We want to generate an ereport in these cases.
+	 */
+	if (deallocation > beentry->backend_allocated_bytes)
+	{
+		ereport(LOG, errmsg("decrease reduces reported backend memory allocated below zero; setting reported to 0"));
+
+		/*
+		 * Overwrite deallocation with current backend_allocated_bytes so we
+		 * end up at zero.
+		 */
+		deallocation = beentry->backend_allocated_bytes;
+	}
+
+	/*
+	 * Update my status entry, following the protocol of bumping
+	 * st_changecount before and after.  We use a volatile pointer here to
+	 * ensure the compiler doesn't try to get cute.
+	 */
+	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
+	beentry->backend_allocated_bytes -= deallocation;
+	PGSTAT_END_WRITE_ACTIVITY(beentry);
+}
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 96bffc0f2a..b6d135ad2f 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -553,7 +553,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_activity(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_ACTIVITY_COLS	30
+#define PG_STAT_GET_ACTIVITY_COLS	31
 	int			num_backends = pgstat_fetch_stat_numbackends();
 	int			curr_backend;
 	int			pid = PG_ARGISNULL(0) ? -1 : PG_GETARG_INT32(0);
@@ -609,6 +609,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[16] = true;
 
+		values[30] = UInt64GetDatum(beentry->backend_allocated_bytes);
+
 		/* Values only available to role member or pg_read_all_stats */
 		if (HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		{
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index b6a8bbcd59..81e62e4981 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -47,6 +47,7 @@
 #include "postgres.h"

 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_backend_allocated_bytes_increase(firstBlockSize);

 	Assert(AllocSetIsValid(set));

 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_backend_allocated_bytes_decrease(deallocation);

 	Assert(AllocSetIsValid(set));

 
 				/* All that remains is to free the header/initial block */
 				free(oldset);
 			}
 			Assert(freelist->num_free == 0);
+			pgstat_report_backend_allocated_bytes_decrease(deallocation);
 		}

 
 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_backend_allocated_bytes_decrease(deallocation +
+												   context->mem_allocated);

 		context->mem_allocated += blksize;
+		pgstat_report_backend_allocated_bytes_increase(blksize);
 
 		block->aset = set;
 
 		context->mem_allocated += blksize;
+		pgstat_report_backend_allocated_bytes_increase(blksize);
 
 		block->aset = set;
 
 		set->header.mem_allocated -= block->endptr - ((char *) block);
+		pgstat_report_backend_allocated_bytes_decrease(block->endptr - ((char *) block));

 		/* updated separately, not to underflow when (oldblksize > blksize) */
 		set->header.mem_allocated -= oldblksize;
+		pgstat_report_backend_allocated_bytes_decrease(oldblksize);
 		set->header.mem_allocated += blksize;
+		pgstat_report_backend_allocated_bytes_increase(blksize);

diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index b432a92be3..df3007edfb 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"
 
 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_backend_allocated_bytes_increase(firstBlockSize);

 	Assert(GenerationIsValid(set));

+	pgstat_report_backend_allocated_bytes_decrease(deallocation);
+
 	/* set it so new allocations to make use of the keeper block */
 	set->block = set->keeper;
 
+	pgstat_report_backend_allocated_bytes_decrease(context->mem_allocated);
 
 		context->mem_allocated += blksize;
+		pgstat_report_backend_allocated_bytes_increase(blksize);

 			context->mem_allocated += blksize;
+			pgstat_report_backend_allocated_bytes_increase(blksize);

 	set->header.mem_allocated -= block->blksize;
+	pgstat_report_backend_allocated_bytes_decrease(block->blksize);
+
 	free(block);
 }
 
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 6df0839b6a..532c038973 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
 
+	/*
+	 * If SlabContextCreate is updated to add headerSize to
+	 * context->mem_allocated, then update here and SlabDelete appropriately
+	 */
+	pgstat_report_backend_allocated_bytes_increase(headerSize);
+
 	return (MemoryContext) slab;
 }

 	Assert(SlabIsValid(slab));

+	pgstat_report_backend_allocated_bytes_decrease(deallocation);
 	slab->minFreeChunks = 0;
 
+	pgstat_report_backend_allocated_bytes_decrease(slab->headerSize);
+		pgstat_report_backend_allocated_bytes_increase(slab->blockSize);
 	}
 
+		pgstat_report_backend_allocated_bytes_decrease(slab->blockSize);
index 20f5aa56ea..1c37f7db5d 100644
+  proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id,backend_allocated_bytes}',
index b582b46e9f..75d87e8308 100644
 
 	/* query identifier, optionally computed using post_parse_analyze_hook */
 	uint64		st_query_id;
+
+	/* Current memory allocated to this backend */
+	uint64		backend_allocated_bytes;
 } PgBackendStatus;

@@ -313,7 +316,9 @@ extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
 extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
 													   int buflen);
 extern uint64 pgstat_get_my_query_id(void);
-
+extern void pgstat_report_backend_allocated_bytes_increase(uint64 allocation);
+extern void pgstat_report_backend_allocated_bytes_decrease(uint64 deallocation);
+extern uint64 pgstat_get_all_backend_memory_allocated(void);
 
 /* ----------
index 624d0e5aae..ba9f494806 100644
@@ -1753,10 +1753,11 @@ pg_stat_activity| SELECT s.datid,
     s.state,
+    s.backend_allocated_bytes,
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_allocated_bytes)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_allocated_bytes)
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_allocated_bytes)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, backend_allocated_bytes)

---

From: Reid Thompson <[email-masked]>
Date: Sat, 26 Nov 2022 22:22:15 -0500

> and backend_xmin fields in pg_stat_activity view, rather than between

rebased/patched to current master && current pg-stat-activity-backend-memory-allocated 

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

From 1470f45e086bef0757cc262d10e08904e46b9a88 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Sat, 4 Jun 2022 22:23:59 -0400
Subject: [PATCH 2/2] Add the ability to limit the amount of memory that can be
 allocated to backends.

 src/backend/utils/activity/backend_status.c   | 108 ++++++++++++++++++
 src/include/utils/backend_status.h            |   3 +
 9 files changed, 197 insertions(+)

index 24b1624bad..c2db3ace7a 100644
 
+        allocations (<varname>allocated_bytes</varname>) are displayed in the
 
index 65d59fc43e..8d9df676af 100644

 
index 3785e8af53..07dfd8f490 100644

 /* exposed so that backend_progress.c can access it */
 PgBackendStatus *MyBEEntry = NULL;
@@ -1236,3 +1239,108 @@ pgstat_reset_allocated_bytes_storage(void)
 	my_allocated_bytes = &local_my_allocated_bytes;
 }
 
+/* ----------
+ * pgstat_get_all_memory_allocated() -
+ *
+	uint64		all_memory_allocated = 0;
+		uint64		allocated_bytes = 0;
+				allocated_bytes = vbeentry->allocated_bytes;
+			all_memory_allocated += allocated_bytes;
+	return all_memory_allocated;
+				errmsg("allocation would exceed max_total_memory limit (%llu > %llu)",
index 349dd6a537..c20a656310 100644
@@ -3423,6 +3423,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
 
 # - Disk -
 
index b202e115b6..596f1db408 100644
 
@@ -741,6 +745,11 @@ AllocSetAlloc(MemoryContext context, Size size)
 #endif
 
@@ -938,6 +947,10 @@ AllocSetAlloc(MemoryContext context, Size size)

@@ -1178,6 +1191,10 @@ AllocSetRealloc(void *pointer, Size size)
 		blksize = chksize + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
 		oldblksize = block->endptr - ((char *) block);
 
index 459eb985d6..145409cf21 100644

 
 
 			if (block == NULL)
index f38256f6f3..9304e13638 100644

 		if (block == NULL)
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index e5aa90b101..94528aa650 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -286,6 +286,7 @@ typedef struct LocalPgBackendStatus
  */
 extern PGDLLIMPORT bool pgstat_track_activities;
 extern PGDLLIMPORT int pgstat_track_activity_query_size;
+extern PGDLLIMPORT int max_total_bkend_mem;

 /* ----------
@@ -325,6 +326,7 @@ extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
 extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
 													   int buflen);
 extern uint64 pgstat_get_my_query_id(void);
+extern uint64 pgstat_get_all_backend_memory_allocated(void);
 extern void pgstat_set_allocated_bytes_storage(uint64 *allocated_bytes);
 extern void pgstat_reset_allocated_bytes_storage(void);
 
@@ -337,6 +339,7 @@ extern int	pgstat_fetch_stat_numbackends(void);
 
 /* ----------
  * pgstat_report_allocated_bytes() -
-- 
2.25.1

From 3d772d8620faba4bd4e091d6618c63557fbf6749 Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

This new field displays the current bytes of memory allocated to the
backend process. It is updated as memory for the process is
malloc'd/free'd. Memory allocated to items on the freelist is included in
the displayed value.  Dynamic shared memory allocations are included
only in the value displayed for the backend that created them, they are
not included in the value for backends that are attached to them to
avoid double counting. On occasion, orphaned memory segments may be
cleaned up on postmaster startup. This may result in decreasing the sum
without a prior increment. We limit the floor of backend_mem_allocated
to zero. Updated pg_stat_activity documentation for the new column.
---
 doc/src/sgml/monitoring.sgml                | 15 ++++
 src/backend/catalog/system_views.sql        |  1 +
 src/backend/postmaster/autovacuum.c         |  6 ++
 src/backend/postmaster/postmaster.c         | 13 ++++
 src/backend/postmaster/syslogger.c          |  3 +
 src/backend/storage/ipc/dsm_impl.c          | 81 +++++++++++++++++++++
 src/backend/utils/activity/backend_status.c | 45 ++++++++++++
 src/backend/utils/adt/pgstatfuncs.c         |  4 +-
 src/backend/utils/mmgr/aset.c               | 17 +++++
 src/backend/utils/mmgr/generation.c         | 15 ++++
 src/backend/utils/mmgr/slab.c               | 21 ++++++
 src/include/catalog/pg_proc.dat             |  6 +-
 src/include/utils/backend_status.h          | 59 ++++++++++++++-
 src/test/regress/expected/rules.out         |  9 ++-
 src/test/regress/expected/stats.out         | 11 +++
 src/test/regress/sql/stats.sql              |  3 +
 16 files changed, 300 insertions(+), 9 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 5579b8b9e0..ffe7d2566c 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -947,6 +947,21 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
      </para></entry>
     </row>
 
+    <row>
+     <entry role="catalog_table_entry"><para role="column_definition">
+      <structfield>allocated_bytes</structfield> <type>bigint</type>
+     </para>
+     <para>
+      Memory currently allocated to this backend in bytes. This is the balance
+      of bytes allocated and freed by this backend. Dynamic shared memory
+      allocations are included only in the value displayed for the backend that
+      created them, they are not included in the value for backends that are
+      attached to them to avoid double counting. Use <function>pg_size_pretty</function>
+      described in <xref linkend="functions-admin-dbsize"/> to make this value
+      more easily readable.
+     </para></entry>
+    </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>query</structfield> <type>text</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 2d8104b090..9ea8f78c95 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -864,6 +864,7 @@ CREATE VIEW pg_stat_activity AS
             S.state,
             S.backend_xid,
             s.backend_xmin,
+            S.allocated_bytes,
             S.query_id,
             S.query,
             S.backend_type
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 601834d4b4..f54606104d 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -407,6 +407,9 @@ StartAutoVacLauncher(void)
 
 #ifndef EXEC_BACKEND
 		case 0:
+			/* Zero allocated bytes to avoid double counting parent allocation */
+			pgstat_zero_my_allocated_bytes();
+
 			/* in postmaster child ... */
 			InitPostmasterChild();
 
@@ -1485,6 +1488,9 @@ StartAutoVacWorker(void)
 
 #ifndef EXEC_BACKEND
 		case 0:
+			/* Zero allocated bytes to avoid double counting parent allocation */
+			pgstat_zero_my_allocated_bytes();
+
 			/* in postmaster child ... */
 			InitPostmasterChild();
 
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index a8a246921f..89a6caec78 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -4102,6 +4102,9 @@ BackendStartup(Port *port)
 	{
 		free(bn);
 
+		/* Zero allocated bytes to avoid double counting parent allocation */
+		pgstat_zero_my_allocated_bytes();
+
 		/* Detangle from postmaster */
 		InitPostmasterChild();
 
@@ -5307,6 +5310,11 @@ StartChildProcess(AuxProcType type)
 		MemoryContextDelete(PostmasterContext);
 		PostmasterContext = NULL;
 
+		/* Zero allocated bytes to avoid double counting parent allocation.
+		 * Needs to be after the MemoryContextDelete(PostmasterContext) above.
+		 */
+		pgstat_zero_my_allocated_bytes();
+
 		AuxiliaryProcessMain(type); /* does not return */
 	}
 #endif							/* EXEC_BACKEND */
@@ -5700,6 +5708,11 @@ do_start_bgworker(RegisteredBgWorker *rw)
 			MemoryContextDelete(PostmasterContext);
 			PostmasterContext = NULL;
 
+			/* Zero allocated bytes to avoid double counting parent allocation.
+			 * Needs to be after the MemoryContextDelete(PostmasterContext) above.
+			 */
+			pgstat_zero_my_allocated_bytes();
+
 			StartBackgroundWorker();
 
 			exit(1);			/* should not get here */
diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.c
index d6d02e3c63..4cbc59cda5 100644
--- a/src/backend/postmaster/syslogger.c
+++ b/src/backend/postmaster/syslogger.c
@@ -679,6 +679,9 @@ SysLogger_Start(void)
 
 #ifndef EXEC_BACKEND
 		case 0:
+			/* Zero allocated bytes to avoid double counting parent allocation */
+			pgstat_zero_my_allocated_bytes();
+
 			/* in postmaster child ... */
 			InitPostmasterChild();
 
index 6ddd46a4e7..65d59fc43e 100644
 
+			pgstat_report_allocated_bytes(*mapped_size, DECREASE);
+			pgstat_report_allocated_bytes(*mapped_size, DECREASE);
+			pgstat_report_allocated_bytes(request_size, INCREASE);
+		pgstat_report_allocated_bytes(*mapped_size, DECREASE);
+		pgstat_report_allocated_bytes(request_size, INCREASE);
+			pgstat_report_allocated_bytes(*mapped_size, DECREASE);
+		pgstat_report_allocated_bytes(request_size, INCREASE);

+		/*
+			pgstat_report_allocated_bytes(*mapped_size, DECREASE);
 
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_allocated_bytes(info.RegionSize, INCREASE);
 	*mapped_address = address;
 	*mapped_size = info.RegionSize;
 	*impl_private = hmap;
@@ -812,6 +879,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		pgstat_report_allocated_bytes(*mapped_size, DECREASE);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && unlink(name) != 0)
@@ -933,6 +1007,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_allocated_bytes(request_size, INCREASE);
 	*mapped_address = address;
 	*mapped_size = request_size;
 
diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index 1146a6c33c..3785e8af53 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -49,6 +49,9 @@ int			pgstat_track_activity_query_size = 1024;
 /* exposed so that backend_progress.c can access it */
 PgBackendStatus *MyBEEntry = NULL;
 
+/* Memory allocated to this backend prior to pgstats initialization */
+uint64	local_my_allocated_bytes = 0;
+uint64	*my_allocated_bytes = &local_my_allocated_bytes;
 
@@ -400,6 +403,15 @@ pgstat_bestart(void)
 
+	/* Alter allocation reporting from local_my_allocated_bytes to shared memory */
+	pgstat_set_allocated_bytes_storage(&MyBEEntry->allocated_bytes);
+
+	/* Populate sum of memory allocated prior to pgstats initialization to pgstats
+	 * and zero the local variable.
+	 */
+	lbeentry.allocated_bytes += local_my_allocated_bytes;
+	local_my_allocated_bytes = 0;
+
 	/*
 	 * we don't zero st_progress_param here to save cycles; nobody should
 	 * examine it until st_progress_command has been set to something other
@@ -459,6 +471,11 @@ pgstat_beshutdown_hook(int code, Datum arg)
 {
 	volatile PgBackendStatus *beentry = MyBEEntry;
 
+	/*
+	 * Stop reporting memory allocation changes to &MyBEEntry->allocated_bytes
+	 */
+	pgstat_reset_allocated_bytes_storage();
+
 	/*
 	 * Clear my status entry, following the protocol of bumping st_changecount
 	 * before and after.  We use a volatile pointer here to ensure the
@@ -1191,3 +1208,31 @@ pgstat_clip_activity(const char *raw_activity)
 
 	return activity;
 }
+
+/*
+ * Configure bytes allocated reporting to report allocated bytes to
+ * *allocated_bytes.  *allocated_bytes needs to be valid until
+ * pgstat_set_allocated_bytes_storage() is called.
+ *
+ * Expected to be called during backend startup (in pgstat_bestart), to point
+ * my_allocated_bytes into shared memory.
+ */
+void
+pgstat_set_allocated_bytes_storage(uint64 *new_allocated_bytes)
+{
+	my_allocated_bytes = new_allocated_bytes;
+	*new_allocated_bytes = local_my_allocated_bytes;
+}
+
+/*
+ * Reset allocated bytes storage location.
+ *
+ * Expected to be called during backend shutdown, before the location set up
+ * by pgstat_set_allocated_bytes_storage() becomes invalid.
+ */
+void
+pgstat_reset_allocated_bytes_storage(void)
+{
+	my_allocated_bytes = &local_my_allocated_bytes;
+}
+
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index ae3365d917..170d60df8b 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -559,7 +559,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_activity(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_ACTIVITY_COLS	30
+#define PG_STAT_GET_ACTIVITY_COLS	31
 	int			num_backends = pgstat_fetch_stat_numbackends();
 	int			curr_backend;
 	int			pid = PG_ARGISNULL(0) ? -1 : PG_GETARG_INT32(0);
@@ -615,6 +615,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[16] = true;
 
+		values[30] = UInt64GetDatum(beentry->allocated_bytes);
+
 		/* Values only available to role member or pg_read_all_stats */
 		if (HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		{
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index b6a8bbcd59..b202e115b6 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -47,6 +47,7 @@
 #include "postgres.h"

 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_allocated_bytes(firstBlockSize, INCREASE);

 

 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_allocated_bytes(deallocation, DECREASE);

 

 				/* All that remains is to free the header/initial block */
 				free(oldset);
 			}
 			Assert(freelist->num_free == 0);
+			pgstat_report_allocated_bytes(deallocation, DECREASE);
 		}

 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -685,6 +696,7 @@ AllocSetDelete(MemoryContext context)
 	}
 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_allocated_bytes(deallocation + context->mem_allocated, DECREASE);
 
 	/* Finally, free the context header, including the keeper block */
 	free(set);
@@ -734,6 +746,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;
 
 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, INCREASE);
 
 		block->aset = set;
 		block->freeptr = block->endptr = ((char *) block) + blksize;
@@ -944,6 +957,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 			return NULL;
 
 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, INCREASE);
 
 		block->aset = set;
 		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -1043,6 +1057,7 @@ AllocSetFree(void *pointer)
 			block->next->prev = block->prev;
 
 		set->header.mem_allocated -= block->endptr - ((char *) block);
+		pgstat_report_allocated_bytes(block->endptr - ((char *) block), DECREASE);
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -1173,7 +1188,9 @@ AllocSetRealloc(void *pointer, Size size)
 
 		/* updated separately, not to underflow when (oldblksize > blksize) */
 		set->header.mem_allocated -= oldblksize;
+		pgstat_report_allocated_bytes(oldblksize, DECREASE);
 		set->header.mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, INCREASE);

diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index b432a92be3..459eb985d6 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"
 
 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_allocated_bytes(firstBlockSize, INCREASE);

 
 
+	pgstat_report_allocated_bytes(deallocation, DECREASE);
+
 	/* set it so new allocations to make use of the keeper block */
 	set->block = set->keeper;
 
+	pgstat_report_allocated_bytes(context->mem_allocated, DECREASE);
 
 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, INCREASE);

 			context->mem_allocated += blksize;
+			pgstat_report_allocated_bytes(blksize, INCREASE);

 	set->header.mem_allocated -= block->blksize;
+	pgstat_report_allocated_bytes(block->blksize, DECREASE);
+
 	free(block);
 }
 
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 6df0839b6a..f38256f6f3 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
 
+	/*
+	 * If SlabContextCreate is updated to add headerSize to
+	 * context->mem_allocated, then update here and SlabDelete appropriately
+	 */
+	pgstat_report_allocated_bytes(headerSize, INCREASE);
+
 	return (MemoryContext) slab;
 }

 
 
+	pgstat_report_allocated_bytes(deallocation, DECREASE);
 	slab->minFreeChunks = 0;
 
+	pgstat_report_allocated_bytes(slab->headerSize, DECREASE);
+		pgstat_report_allocated_bytes(slab->blockSize, INCREASE);
 	}
 
 	/* grab the block from the freelist (even the new block is there) */
@@ -537,6 +557,7 @@ SlabFree(void *pointer)
 		free(block);
 		slab->nblocks--;
 		slab->header.mem_allocated -= slab->blockSize;
+		pgstat_report_allocated_bytes(slab->blockSize, DECREASE);
 	}
 	else
 		dlist_push_head(&slab->freelist[block->nfree], &block->node);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index f9301b2627..1bf02758d4 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5373,9 +5373,9 @@
   proname => 'pg_stat_get_activity', prorows => '100', proisstrict => 'f',
   proretset => 't', provolatile => 's', proparallel => 'r',
   prorettype => 'record', proargtypes => 'int4',
-  proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,text,numeric,text,bool,text,bool,int4,int8}',
-  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id}',
+  proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,text,numeric,text,bool,text,bool,int4,int8,int8}',
+  proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id,allocated_bytes}',
   prosrc => 'pg_stat_get_activity' },
 { oid => '3318',
   descr => 'statistics: information about progress of backends running maintenance command',
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index b582b46e9f..e5aa90b101 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -15,6 +15,7 @@
 #include "miscadmin.h"			/* for BackendType */
 #include "storage/backendid.h"
 #include "utils/backend_progress.h"
+#include "common/int.h"

 /* ----------
@@ -32,6 +33,13 @@ typedef enum BackendState
 	STATE_DISABLED
 } BackendState;
 
+/* Enum helper for reporting memory allocated bytes */
+enum allocation_direction
+{
+	DECREASE = -1,
+	IGNORE,
+	INCREASE,
+};
 
 /* ----------
  * Shared-memory data structures
@@ -169,6 +177,9 @@ typedef struct PgBackendStatus
 
 	/* query identifier, optionally computed using post_parse_analyze_hook */
 	uint64		st_query_id;
+
+	/* Current memory allocated to this backend */
+	uint64		allocated_bytes;
 } PgBackendStatus;

@@ -282,6 +293,7 @@ extern PGDLLIMPORT int pgstat_track_activity_query_size;
  * ----------
  */
 extern PGDLLIMPORT PgBackendStatus *MyBEEntry;
+extern PGDLLIMPORT uint64 *my_allocated_bytes;

 /* ----------
@@ -313,7 +325,8 @@ extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
 extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
 													   int buflen);
 extern uint64 pgstat_get_my_query_id(void);
-
+extern void pgstat_set_allocated_bytes_storage(uint64 *allocated_bytes);
+extern void pgstat_reset_allocated_bytes_storage(void);
 
 /* ----------
  * Support functions for the SQL-callable functions to
@@ -325,5 +338,49 @@ extern PgBackendStatus *pgstat_fetch_stat_beentry(BackendId beid);
 extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 extern char *pgstat_clip_activity(const char *raw_activity);
 
+/* ----------
+ * pgstat_report_allocated_bytes() -
+ *
+ *  Called to report change in memory allocated for this backend.
+ *
+ * my_allocated_bytes initially points to local memory, making it safe to call
+ * this before pgstats has been initialized. allocation_direction is a
+ * positive/negative multiplier enum defined above.
+ * ----------
+ */
+static inline void
+pgstat_report_allocated_bytes(uint64 allocated_bytes, int allocation_direction)
+{
+	uint64 temp;
+
+	/* Avoid *my_allocated_bytes unsigned integer overflow on DECREASE */
+	if (allocation_direction == DECREASE &&
+		pg_sub_u64_overflow(*my_allocated_bytes, allocated_bytes, &temp))
+	{
+		*my_allocated_bytes = 0;
+		ereport(LOG,
+				errmsg("Backend %d deallocated %ld bytes, exceeding the %ld bytes it is currently reporting allocated. Setting reported to 0.",
+					   MyProcPid, allocated_bytes, *my_allocated_bytes));
+	}
+	else
+		*my_allocated_bytes += (allocated_bytes) * allocation_direction;
+
+	return;
+}
+
+/* ---------
+ * pgstat_zero_my_allocated_bytes() -
+ *
+ * Called to zero out local allocated bytes variable after fork to avoid double
+ * counting allocations.
+ * ---------
+ */
+static inline void
+pgstat_zero_my_allocated_bytes(void)
+{
+	*my_allocated_bytes = 0;
+
+    return;
+}
 
 #endif							/* BACKEND_STATUS_H */
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 37c1c86473..5263294ad4 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1756,10 +1756,11 @@ pg_stat_activity| SELECT s.datid,
     s.state,
     s.backend_xid,
     s.backend_xmin,
+    s.allocated_bytes,
     s.query_id,
     s.query,
     s.backend_type
-   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, allocated_bytes)
      LEFT JOIN pg_database d ON ((s.datid = d.oid)))
      LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
 pg_stat_all_indexes| SELECT c.oid AS relid,
@@ -1874,7 +1875,7 @@ pg_stat_gssapi| SELECT s.pid,
     s.gss_auth AS gss_authenticated,
     s.gss_princ AS principal,
     s.gss_enc AS encrypted
-   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, allocated_bytes)
   WHERE (s.client_port IS NOT NULL);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
@@ -2055,7 +2056,7 @@ pg_stat_replication| SELECT s.pid,
     w.sync_priority,
     w.sync_state,
     w.reply_time
-   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, allocated_bytes)
      JOIN pg_stat_get_wal_senders() w(pid, state, sent_lsn, write_lsn, flush_lsn, replay_lsn, write_lag, flush_lag, replay_lag, sync_priority, sync_state, reply_time) ON ((s.pid = w.pid)))
      LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
 pg_stat_replication_slots| SELECT s.slot_name,
@@ -2089,7 +2090,7 @@ pg_stat_ssl| SELECT s.pid,
     s.ssl_client_dn AS client_dn,
     s.ssl_client_serial AS client_serial,
     s.ssl_issuer_dn AS issuer_dn
-   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id)
+   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid, query_id, allocated_bytes)
   WHERE (s.client_port IS NOT NULL);
 pg_stat_subscription| SELECT su.oid AS subid,
     su.subname,
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 1d84407a03..ab7e95c367 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -1126,4 +1126,15 @@ SELECT pg_stat_get_subscription_stats(NULL);
  
 (1 row)
 
+-- ensure that allocated_bytes exist for backends
+SELECT allocated_bytes > 0 AS result FROM pg_stat_activity WHERE backend_type
+IN ('checkpointer', 'background writer', 'walwriter', 'autovacuum launcher');
+ result 
+--------
+ t
+ t
+ t
+ t
+(4 rows)
+
 -- End of Stats Test
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index b4d6753c71..2f0b1cc9d8 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -535,5 +535,8 @@ SET enable_seqscan TO on;
 SELECT pg_stat_get_replication_slot(NULL);
 SELECT pg_stat_get_subscription_stats(NULL);
 
+-- ensure that allocated_bytes exist for backends
+SELECT allocated_bytes > 0 AS result FROM pg_stat_activity WHERE backend_type
+IN ('checkpointer', 'background writer', 'walwriter', 'autovacuum launcher');
 
 -- End of Stats Test
-- 
2.25.1

---

From: Andres Freund <[email-masked]>
Date: Tue, 6 Dec 2022 10:32:44 -0800

Hi,

> rebased/patched to current master && current pg-stat-activity-backend-memory-allocated

This version fails to build with msvc, and builds with warnings on other
platforms.
https://cirrus-ci.com/build/5410696721072128
msvc:
[20:26:51.286] c:\cirrus\src\include\utils/backend_status.h(40): error C2059: syntax error: 'constant'

mingw cross:
[20:26:26.358]                  from /usr/share/mingw-w64/include/winsock2.h:23,
[20:26:26.358]                  from ../../src/include/port/win32_port.h:60,
[20:26:26.358]                  from ../../src/include/port.h:24,
[20:26:26.358]                  from ../../src/include/c.h:1306,
[20:26:26.358]                  from ../../src/include/postgres.h:47,
[20:26:26.358]                  from controldata_utils.c:18:
[20:26:26.358] ../../src/include/utils/backend_status.h:40:2: error: expected identifier before numeric constant
[20:26:26.358]    40 |  IGNORE,
[20:26:26.358]       |  ^~~~~~
[20:26:26.358] In file included from ../../src/include/postgres.h:48,
[20:26:26.358]                  from controldata_utils.c:18:
[20:26:26.358] ../../src/include/utils/backend_status.h: In function ‘pgstat_report_allocated_bytes’:
[20:26:26.358] ../../src/include/utils/backend_status.h:365:12: error: format ‘%ld’ expects argument of type ‘long int’, but argument 3 has type ‘uint64’ {aka ‘long long unsigned int’} [-Werror=format=]
[20:26:26.358]   365 |     errmsg("Backend %d deallocated %ld bytes, exceeding the %ld bytes it is currently reporting allocated. Setting reported to 0.",
[20:26:26.358]       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[20:26:26.358]   366 |         MyProcPid, allocated_bytes, *my_allocated_bytes));
[20:26:26.358]       |                    ~~~~~~~~~~~~~~~
[20:26:26.358]       |                    |
[20:26:26.358]       |                    uint64 {aka long long unsigned int}

Due to windows having long be 32bit, you need to use %lld. Our custom to deal
with that is to cast the argument to errmsg as long long unsigned and use
%llu.

Btw, given that the argument is uint64, it doesn't seem correct to use %ld,
that's signed. Not that it's going to matter, but ...

Greetings,

Andres Freund

---

From: Reid Thompson <[email-masked]>
Date: Fri, 09 Dec 2022 10:05:45 -0500

> https://cirrus-ci.com/build/5410696721072128

updated patches

-- 
Reid Thompson
Senior Software Engineer
Crunchy Data, Inc.

From e48292eaf402bfe397f1c2fdc1b3efd8cd0a9137 Mon Sep 17 00:00:00 2001

index ff6fcd902a..2899f109ac 100644

index 36ef3e425e..58fb690c69 100644

 

 
+/* ----------
index 1bf14eec66..bfde338a8d 100644
 
+	{
index 043864597f..75ea0c9af1 100644
 
 # - Disk -
 
index cc10dfd609..3ce2191555 100644

 

index b0460d97c2..3183c9a8dc 100644

 
 
 			if (block == NULL)
index 08bb013f7c..2074f3853a 100644

 		if (block == NULL)
index 3ba479cb0d..1787d75ace 100644

 /* ----------

 /* ----------

From fdb7e6d5bb653e9c5031fd058bf168bdf80a20eb Mon Sep 17 00:00:00 2001
From: Reid Thompson <[email-masked]>
Date: Thu, 11 Aug 2022 12:01:25 -0400
Subject: [PATCH 1/2] Add tracking of backend memory allocated to
 pg_stat_activity

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 11a8ebe5ec..13ecbe5877 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -948,6 +948,21 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
      </para></entry>
     </row>
 
+    <row>
index 0746d80224..f6b6f71cdb 100644
 
 #ifndef EXEC_BACKEND
 		case 0:

 #ifndef EXEC_BACKEND
 		case 0:

 

 
 
 #ifndef EXEC_BACKEND
 		case 0:
 
index 6ddd46a4e7..36ef3e425e 100644
 
+			pgstat_report_allocated_bytes(*mapped_size, PG_ALLOC_DECREASE);
+			pgstat_report_allocated_bytes(request_size - *mapped_size,
+										  PG_ALLOC_INCREASE);
+		pgstat_report_allocated_bytes(*mapped_size, PG_ALLOC_DECREASE);
+		pgstat_report_allocated_bytes(request_size, PG_ALLOC_INCREASE);
+			pgstat_report_allocated_bytes(*mapped_size, PG_ALLOC_DECREASE);
+		pgstat_report_allocated_bytes(request_size, PG_ALLOC_INCREASE);

+		/*
+			pgstat_report_allocated_bytes(*mapped_size, PG_ALLOC_DECREASE);
 
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_allocated_bytes(info.RegionSize, PG_ALLOC_INCREASE);
 	*mapped_address = address;
 	*mapped_size = info.RegionSize;
 	*impl_private = hmap;
@@ -812,6 +879,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 							name)));
 			return false;
 		}
+
+		/*
+		 * Detach and destroy pass through here, only decrease the memory
+		 * shown allocated in pg_stat_activity when the creator destroys the
+		 * allocation.
+		 */
+		pgstat_report_allocated_bytes(*mapped_size, PG_ALLOC_DECREASE);
 		*mapped_address = NULL;
 		*mapped_size = 0;
 		if (op == DSM_OP_DESTROY && unlink(name) != 0)
@@ -933,6 +1007,13 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
 						name)));
 		return false;
 	}
+
+	/*
+	 * Attach and create pass through here, only update backend memory
+	 * allocated in pg_stat_activity for the creator process.
+	 */
+	if (op == DSM_OP_CREATE)
+		pgstat_report_allocated_bytes(request_size, PG_ALLOC_INCREASE);
 	*mapped_address = address;
 	*mapped_size = request_size;

 

+	/*
 
 	return activity;
 }
+
+/*
index 25a159b5e5..c4350cfa50 100644
@@ -302,7 +302,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
@@ -358,6 +358,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[16] = true;
 
index b6a8bbcd59..cc10dfd609 100644

 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_allocated_bytes(firstBlockSize, PG_ALLOC_INCREASE);

 

 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_allocated_bytes(deallocation, PG_ALLOC_DECREASE);

 

 				/* All that remains is to free the header/initial block */
 				free(oldset);
 			}
 			Assert(freelist->num_free == 0);
+			pgstat_report_allocated_bytes(deallocation, PG_ALLOC_DECREASE);
 		}

 
 
 	Assert(context->mem_allocated == keepersize);
+	pgstat_report_allocated_bytes(deallocation + context->mem_allocated, PG_ALLOC_DECREASE);

 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, PG_ALLOC_INCREASE);
 
 		block->aset = set;
 
 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, PG_ALLOC_INCREASE);
 
 		block->aset = set;
 
 		set->header.mem_allocated -= block->endptr - ((char *) block);
+		pgstat_report_allocated_bytes(block->endptr - ((char *) block), PG_ALLOC_DECREASE);

 		/* updated separately, not to underflow when (oldblksize > blksize) */
 		set->header.mem_allocated -= oldblksize;
+		pgstat_report_allocated_bytes(oldblksize, PG_ALLOC_DECREASE);
 		set->header.mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, PG_ALLOC_INCREASE);

diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index b432a92be3..b0460d97c2 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -37,6 +37,7 @@
 
 #include "lib/ilist.h"
 
 	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	pgstat_report_allocated_bytes(firstBlockSize, PG_ALLOC_INCREASE);

 
 
+	pgstat_report_allocated_bytes(deallocation, PG_ALLOC_DECREASE);
+
 	/* set it so new allocations to make use of the keeper block */
 	set->block = set->keeper;
 
+	pgstat_report_allocated_bytes(context->mem_allocated, PG_ALLOC_DECREASE);
 
 		context->mem_allocated += blksize;
+		pgstat_report_allocated_bytes(blksize, PG_ALLOC_INCREASE);

 			context->mem_allocated += blksize;
+			pgstat_report_allocated_bytes(blksize, PG_ALLOC_INCREASE);

 	set->header.mem_allocated -= block->blksize;
+	pgstat_report_allocated_bytes(block->blksize, PG_ALLOC_DECREASE);
+
 	free(block);
 }
 
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 6df0839b6a..08bb013f7c 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -53,6 +53,7 @@
 #include "postgres.h"
 
 #include "lib/ilist.h"
 
+	/*
+	 * If SlabContextCreate is updated to add headerSize to
+	 * context->mem_allocated, then update here and SlabDelete appropriately
+	 */
+	pgstat_report_allocated_bytes(headerSize, PG_ALLOC_INCREASE);
+
 	return (MemoryContext) slab;
 }

 
 
+	pgstat_report_allocated_bytes(deallocation, PG_ALLOC_DECREASE);
 	slab->minFreeChunks = 0;
 
+	pgstat_report_allocated_bytes(slab->headerSize, PG_ALLOC_DECREASE);
+		pgstat_report_allocated_bytes(slab->blockSize, PG_ALLOC_INCREASE);
 	}
 
+		pgstat_report_allocated_bytes(slab->blockSize, PG_ALLOC_DECREASE);
index b582b46e9f..3ba479cb0d 100644

 /* ----------
 
+/* Enum helper for reporting memory allocated bytes */
+enum allocation_direction
+{
+	PG_ALLOC_DECREASE = -1,
+	PG_ALLOC_IGNORE,
+	PG_ALLOC_INCREASE,
+};
 
 /* ----------

 /* ----------
 
 /* ----------
 
+/* ----------
+ * pgstat_report_allocated_bytes() -
+ *
+ *  Called to report change in memory allocated for this backend.
+ *
+ * my_allocated_bytes initially points to local memory, making it safe to call
+ * this before pgstats has been initialized. allocation_direction is a
+ * positive/negative multiplier enum defined above.
+ * ----------
+ */
+static inline void
+pgstat_report_allocated_bytes(int64 allocated_bytes, int allocation_direction)
+{
+	uint64 temp;
+
+	/* Avoid *my_allocated_bytes unsigned integer overflow on PG_ALLOC_DECREASE */
+	if (allocation_direction == PG_ALLOC_DECREASE &&
+		pg_sub_u64_overflow(*my_allocated_bytes, allocated_bytes, &temp))
+	{
+		*my_allocated_bytes = 0;
+		ereport(LOG,
+				errmsg("Backend %d deallocated %lld bytes, exceeding the %llu bytes it is currently reporting allocated. Setting reported to 0.",
+					   MyProcPid, (long long)allocated_bytes, (unsigned long long)*my_allocated_bytes));
+	}
+	else
+		*my_allocated_bytes += (allocated_bytes) * allocation_direction;
+
+	return;
+}
+
+/* ---------
+ * pgstat_zero_my_allocated_bytes() -
+ *
+ * Called to zero out local allocated bytes variable after fork to avoid double
+ * counting allocations.
+ * ---------
+ */
+static inline void
+pgstat_zero_my_allocated_bytes(void)
+{
+	*my_allocated_bytes = 0;
+
+    return;
+}
 
index fb9f936d43..5f854aab18 100644
  
 (1 row)

 
 -- End of Stats Test
-- 
2.25.1