agora inbox for pgsql-hackers@postgresql.org
help / color / mirror / Atom feedFrom: Dmitry Dolgov <9erthalion6@gmail.com>
To: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: pgsql-hackers@postgresql.org, Jack Ng <Jack.Ng@huawei.com>
Cc: Ni Ku <jakkuniku@gmail.com>
Subject: Re: Changing shared_buffers without restart
Date: Fri, 20 Jun 2025 12:19:31 +0200
Message-ID: <my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2> (raw)
In-Reply-To: <CAExHW5sYg_d4O7oGRqbomnVODeqR3YNAeYAa526n1dsWCM=+Fg@mail.gmail.com>
References: <CAExHW5s1b-_9GFGGOxSVimrt8oe2Y0a7vRhENrd2BSo+0Tkp-A@mail.gmail.com>
<gzb2oqqabzqidlnumrbau2k2fscb5jo6nlpdjnf6pu5y4bk5mo@xoujqgtiqvgr>
<CAExHW5uGozdiDm_BefS7jpQzaisCs4_nLTMF0+S_Pds49pRG_w@mail.gmail.com>
<ufa7sghbf3fv7jobgd4yc5am4lzqf7bn2cigqv6cpi6vtkmbah@flj6n76hdgab>
<CA+hUKG+KFbOhPudfcuHaa4TPsZxQ053LnXri2vYfeFNTo+WYjQ@mail.gmail.com>
<CA+hUKGLfdc6gbXc0bE6R_TukCMzbKLvgjZsLtfyPxQOnOaGivw@mail.gmail.com>
<kwvbsat7reeopjhwopfypwdhsfrcev7nmmltec5ec6zzkjol5o@itpqaokfw7kb>
<CA+hUKGLQhsZ1dEf5Zo6JuPbs6n-qX=cTGy49feKf1iFA_TBP1g@mail.gmail.com>
<CAExHW5v9cE+ETusTafZyvy+eVpnVvoayVm7ZOk4Ddq8fxY270A@mail.gmail.com>
<CAExHW5sYg_d4O7oGRqbomnVODeqR3YNAeYAa526n1dsWCM=+Fg@mail.gmail.com>
Hi,
> On Mon, Apr 21, 2025 at 7:47 PM Thomas Munro <thomas.munro@gmail.com>
> wrote:
>
> One thing I'm still wondering about is whether you really need all
> this multi-phase barrier stuff, or even need to stop other backends
> from running at all while doing the resize. I guess that's related to
> your remapping scheme, but supposing you find the simple
> ftruncate()-only approach to be good, my next question is: why isn't
> it enough to wait for all backends to agree to stop allocating new
> buffers in the range to be truncated, and then left them continue to
> run as normal? As far as they would be concerned, the in-progress
> downsize has already happened, though it could be reverted later if
> the eviction phase fails. Then the coordinator could start evicting
> buffers and truncating the shared memory object, which are
> phases/steps, sure, but it's not clear to me why they need other
> backends' help.
My intention behind keeping all backends waiting was to have a simple way of
not only preventing them from allocating new buffers from the truncated range,
but also eliminating any chance of them accessing those to-be-truncated
buffers. In the end it's just easier (at least for me) to reason about
correctness of the implementation this way.
> On Tue, Jun 10, 2025 at 04:39:58PM +0530, Ashutosh Bapat wrote:
>
> Here's patchset rebased on f85f6ab051b7cf6950247e5fa6072c4130613555
Thanks! I've reworked the series to implement approach suggested by
Thomas, and applied your patches to support buffers shrinking on top. I
had to restructure the patch set, here is how it looks like right now:
1. Preparation patches
Changes, that are needed to support resizing functionality, but not
strictly related to it.
* Process config reload in AIO workers. Corrects omission discussed on [1].
* Introduce pending flag for GUC assign hooks. Allowing to decouple a GUC value
change from actually applying it, sort of "pending" change. The idea is to let
a custom logic be triggered on an assign hook, and then take responsibility for
what happens later and how it's going to be applied. Doesn't do GUC reporting
yet.
* Introduce pss_barrierReceivedGeneration. Allows to distinguish situations
when a signal was processed everywhere, and when a signal was received
everywhere.
2. Resizing implementation
* Allow to use multiple shared memory mappings. A preparation patch, extending
the existing interface to support multiple shared memory segments.
* Address space reservation for shared memory. Implement the new way of
handling shared memory segments, now each segment can visually be represented
as following:
/ Address space \
+---------------<+>--------------------------+
| Actual content | Address space reservation |
| (memfd) | (mmap, PROT_NONE) |
+---------------<+>--------------------------+
The actual segment size is managed via ftruncate and mprotect. One interesting
side effect I haven't fully understood yet, is that Linux doesn't seem to
extend the existing mapping when doing mprotect on huge pages, it creates
another mapping instead. E.g. when using normal page size and resizing shared
memory we get:
7f4808600000-7f4817e00000 rw-s /memfd:buffers (deleted)
7f4817e00000-7f48a2000000 ---s /memfd:buffers (deleted)
Doing the same with huge pages ends up looking like this:
7f4808600000-7f4817e00000 rw-s /memfd:buffers (deleted)
7f4817e00000-7f4830000000 rw-s /memfd:buffers (deleted)
7f4830000000-7f48a2000000 ---s /memfd:buffers (deleted)
I'm still investigating whether it's a mistake on my side or a genuine Linux
behavior. At the same time I don't see it as a large issue, the same situation
could happen with the previous implementation as well.
* Introduce multiple shmem segments for shared buffers. Modifies necessary bits
to use new functionality.
* Allow to resize shared memory without restart. Utilizes infrastructure
introduced so far to implement stop-the-world resizing approach, where all the
active backend (and potentially new one spawning) are waiting until everyone
gets the same shared memory size.
When testing I've noticed that there seems to be concurrency issues with
interrupts, where aio workers and checkpointer sometimes do not receive
the resize signal correctly. I assume it has something to do with the
significant behavior change -- config reload processing can now fire
signals on its own. Letting those backends to always process config
reload first seems to be resolved (or at least hide) the issue, but I
still need to understand what's going on there.
3. Shared memory shrinking
So far only shared memory increase was implemented. These patches from Ashutosh
support shrinking as well, which is tricky due to the need for buffer eviction.
* Support shrinking shared buffers
* Reinitialize StrategyControl after resizing buffers
* Additional validation for buffer in the ring
> 0009 adds support to shrink shared buffers. It has two changes: a.
> evict the buffers outside the new buffer size b. remove buffers with
> buffer id outside the new buffer size from the free list. If a buffer
> being evicted is pinned, the operation is aborted and a FATAL error is
> raised. I think we need to change this behaviour to be less severe
> like rolling back the operation or waiting for the pinned buffer to be
> unpinned etc. Better even if we could let users control the behaviour.
> But we need better infrastructure to do such things. That's one TODO
> left in the patch.
I haven't reviewed those, just tested a bit to finally include into the series.
Note that I had to tweak two things:
* The way it was originally implemented was sending resize signal to postmaster
before doing eviction, which could result in sigbus when accessing LSN of a
dirty buffer to be evicted. I've reshaped it a bit to make sure eviction always
happens first.
* It seems the CurrentResource owner could be missing sometimes, so I've added
a band-aid checking its presence.
One side note, during my testing I've noticed assert failures on
pgstat_tracks_io_op inside a wal writer a few times. I couldn't reproduce it
after the fixes above, but still it may indicate that something is off. E.g.
it's somehow not expected that the wal writer will do buffer eviction IO (from
what I understand, the current shrinking implementation allows that).
> Buffer lookup table resizing
> ------------------------------------
> The size of the buffer lookup table depends upon (number of shared
> buffers + number of partitions in the shared buffer lookup table). If we
> shrink the buffer pool, the buffer lookup table will become sparse but
> still useful. If we expand the buffers we need to expand the buffer lookup
> table too. That's not implemented in the current patchset.
Just FYI, buffer lookup table has its own STRATEGY_SHMEM_SEGMENT shared memory
segment and is resized in the same way as others. There could be lots of
details missing, but at least the corresponding resizable segment is already
there.
[1]: https://www.postgresql.org/message-id/flat/sh5uqe4a4aqo5zkkpfy5fobe2rg2zzouctdjz7kou4t74c66ql%40yzpk...
From 5d4f46dc13bacf9c1df79233f8e4017a9dcd6919 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 15:14:33 +0200
Subject: [PATCH v5 01/10] Process config reload in AIO workers
Currenly AIO workers process interrupts only via CHECK_FOR_INTERRUPTS,
which does not include ConfigReloadPending. Thus we need to check for it
explicitly.
---
src/backend/storage/aio/method_worker.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/src/backend/storage/aio/method_worker.c b/src/backend/storage/aio/method_worker.c
index 36be179678d..b4d5c46fb94 100644
--- a/src/backend/storage/aio/method_worker.c
+++ b/src/backend/storage/aio/method_worker.c
@@ -80,6 +80,7 @@ static void pgaio_worker_shmem_init(bool first_time);
static bool pgaio_worker_needs_synchronous_execution(PgAioHandle *ioh);
static int pgaio_worker_submit(uint16 num_staged_ios, PgAioHandle **staged_ios);
+static void pgaio_worker_process_interrupts(void);
const IoMethodOps pgaio_worker_ops = {
.shmem_size = pgaio_worker_shmem_size,
@@ -461,6 +462,8 @@ IoWorkerMain(const void *startup_data, size_t startup_data_len)
int nwakeups = 0;
int worker;
+ pgaio_worker_process_interrupts();
+
/*
* Try to get a job to do.
*
@@ -584,3 +587,25 @@ pgaio_workers_enabled(void)
{
return io_method == IOMETHOD_WORKER;
}
+
+/*
+ * Process any new interrupts.
+ */
+static void
+pgaio_worker_process_interrupts(void)
+{
+ /*
+ * Reloading config can trigger further signals, complicating interrupts
+ * processing -- so let it run first.
+ *
+ * XXX: Is there any need in memory barrier after ProcessConfigFile?
+ */
+ if (ConfigReloadPending)
+ {
+ ConfigReloadPending = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ }
+
+ if (ProcSignalBarrierPending)
+ ProcessProcSignalBarrier();
+}
--
2.49.0
From fd29084b3221e1901a1f07656d4e7abb31335caf Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Sun, 6 Apr 2025 16:40:32 +0200
Subject: [PATCH v5 02/10] Introduce pending flag for GUC assign hooks
Currently an assing hook can perform some preprocessing of a new value,
but it cannot change the behavior, which dictates that the new value
will be applied immediately after the hook. Certain GUC options (like
shared_buffers, coming in subsequent patches) may need coordinating work
between backends to change, meaning we cannot apply it right away.
Add a new flag "pending" for an assign hook to allow the hook indicate
exactly that. If the pending flag is set after the hook, the new value
will not be applied and it's handling becomes the hook's implementation
responsibility.
Note, that this also requires changes in the way how GUCs are getting
reported, but the patch does not cover that yet.
---
src/backend/access/transam/xlog.c | 2 +-
src/backend/commands/variable.c | 6 +--
src/backend/libpq/pqcomm.c | 8 ++--
src/backend/tcop/postgres.c | 2 +-
src/backend/utils/misc/guc.c | 59 +++++++++++++++++++---------
src/backend/utils/misc/stack_depth.c | 2 +-
src/include/utils/guc.h | 2 +-
src/include/utils/guc_hooks.h | 20 +++++-----
8 files changed, 61 insertions(+), 40 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 47ffc0a2307..d1be780683b 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2321,7 +2321,7 @@ CalculateCheckpointSegments(void)
}
void
-assign_max_wal_size(int newval, void *extra)
+assign_max_wal_size(int newval, void *extra, bool *pending)
{
max_wal_size_mb = newval;
CalculateCheckpointSegments();
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 608f10d9412..e40dae2ddf2 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -1143,7 +1143,7 @@ check_cluster_name(char **newval, void **extra, GucSource source)
* GUC assign_hook for maintenance_io_concurrency
*/
void
-assign_maintenance_io_concurrency(int newval, void *extra)
+assign_maintenance_io_concurrency(int newval, void *extra, bool *pending)
{
/*
* Reconfigure recovery prefetching, because a setting it depends on
@@ -1161,12 +1161,12 @@ assign_maintenance_io_concurrency(int newval, void *extra)
* they may be assigned in either order.
*/
void
-assign_io_max_combine_limit(int newval, void *extra)
+assign_io_max_combine_limit(int newval, void *extra, bool *pending)
{
io_combine_limit = Min(newval, io_combine_limit_guc);
}
void
-assign_io_combine_limit(int newval, void *extra)
+assign_io_combine_limit(int newval, void *extra, bool *pending)
{
io_combine_limit = Min(io_max_combine_limit, newval);
}
diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index e5171467de1..2a6a587ef76 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -1952,7 +1952,7 @@ pq_settcpusertimeout(int timeout, Port *port)
* GUC assign_hook for tcp_keepalives_idle
*/
void
-assign_tcp_keepalives_idle(int newval, void *extra)
+assign_tcp_keepalives_idle(int newval, void *extra, bool *pending)
{
/*
* The kernel API provides no way to test a value without setting it; and
@@ -1985,7 +1985,7 @@ show_tcp_keepalives_idle(void)
* GUC assign_hook for tcp_keepalives_interval
*/
void
-assign_tcp_keepalives_interval(int newval, void *extra)
+assign_tcp_keepalives_interval(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_setkeepalivesinterval(newval, MyProcPort);
@@ -2008,7 +2008,7 @@ show_tcp_keepalives_interval(void)
* GUC assign_hook for tcp_keepalives_count
*/
void
-assign_tcp_keepalives_count(int newval, void *extra)
+assign_tcp_keepalives_count(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_setkeepalivescount(newval, MyProcPort);
@@ -2031,7 +2031,7 @@ show_tcp_keepalives_count(void)
* GUC assign_hook for tcp_user_timeout
*/
void
-assign_tcp_user_timeout(int newval, void *extra)
+assign_tcp_user_timeout(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_settcpusertimeout(newval, MyProcPort);
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 2f8c3d5f918..0d1b6466d1e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3591,7 +3591,7 @@ check_log_stats(bool *newval, void **extra, GucSource source)
/* GUC assign hook for transaction_timeout */
void
-assign_transaction_timeout(int newval, void *extra)
+assign_transaction_timeout(int newval, void *extra, bool *pending)
{
if (IsTransactionState())
{
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 667df448732..bb681f5bc60 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1679,6 +1679,7 @@ InitializeOneGUCOption(struct config_generic *gconf)
struct config_int *conf = (struct config_int *) gconf;
int newval = conf->boot_val;
void *extra = NULL;
+ bool pending = false;
Assert(newval >= conf->min);
Assert(newval <= conf->max);
@@ -1687,9 +1688,13 @@ InitializeOneGUCOption(struct config_generic *gconf)
elog(FATAL, "failed to initialize %s to %d",
conf->gen.name, newval);
if (conf->assign_hook)
- conf->assign_hook(newval, extra);
- *conf->variable = conf->reset_val = newval;
- conf->gen.extra = conf->reset_extra = extra;
+ conf->assign_hook(newval, extra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = conf->reset_val = newval;
+ conf->gen.extra = conf->reset_extra = extra;
+ }
break;
}
case PGC_REAL:
@@ -2041,13 +2046,18 @@ ResetAllOptions(void)
case PGC_INT:
{
struct config_int *conf = (struct config_int *) gconf;
+ bool pending = false;
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
- conf->reset_extra);
- *conf->variable = conf->reset_val;
- set_extra_field(&conf->gen, &conf->gen.extra,
- conf->reset_extra);
+ conf->reset_extra,
+ &pending);
+ if (!pending)
+ {
+ *conf->variable = conf->reset_val;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ conf->reset_extra);
+ }
break;
}
case PGC_REAL:
@@ -2424,16 +2434,21 @@ AtEOXact_GUC(bool isCommit, int nestLevel)
struct config_int *conf = (struct config_int *) gconf;
int newval = newvalue.val.intval;
void *newextra = newvalue.extra;
+ bool pending = false;
if (*conf->variable != newval ||
conf->gen.extra != newextra)
{
if (conf->assign_hook)
- conf->assign_hook(newval, newextra);
- *conf->variable = newval;
- set_extra_field(&conf->gen, &conf->gen.extra,
- newextra);
- changed = true;
+ conf->assign_hook(newval, newextra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = newval;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ newextra);
+ changed = true;
+ }
}
break;
}
@@ -3850,18 +3865,24 @@ set_config_with_handle(const char *name, config_handle *handle,
if (changeVal)
{
+ bool pending = false;
+
/* Save old value to support transaction abort */
if (!makeDefault)
push_old_value(&conf->gen, action);
if (conf->assign_hook)
- conf->assign_hook(newval, newextra);
- *conf->variable = newval;
- set_extra_field(&conf->gen, &conf->gen.extra,
- newextra);
- set_guc_source(&conf->gen, source);
- conf->gen.scontext = context;
- conf->gen.srole = srole;
+ conf->assign_hook(newval, newextra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = newval;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ newextra);
+ set_guc_source(&conf->gen, source);
+ conf->gen.scontext = context;
+ conf->gen.srole = srole;
+ }
}
if (makeDefault)
{
diff --git a/src/backend/utils/misc/stack_depth.c b/src/backend/utils/misc/stack_depth.c
index 8f7cf531fbc..ef59ae62008 100644
--- a/src/backend/utils/misc/stack_depth.c
+++ b/src/backend/utils/misc/stack_depth.c
@@ -156,7 +156,7 @@ check_max_stack_depth(int *newval, void **extra, GucSource source)
/* GUC assign hook for max_stack_depth */
void
-assign_max_stack_depth(int newval, void *extra)
+assign_max_stack_depth(int newval, void *extra, bool *pending)
{
ssize_t newval_bytes = newval * (ssize_t) 1024;
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index f619100467d..8802ad8a3cb 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -187,7 +187,7 @@ typedef bool (*GucStringCheckHook) (char **newval, void **extra, GucSource sourc
typedef bool (*GucEnumCheckHook) (int *newval, void **extra, GucSource source);
typedef void (*GucBoolAssignHook) (bool newval, void *extra);
-typedef void (*GucIntAssignHook) (int newval, void *extra);
+typedef void (*GucIntAssignHook) (int newval, void *extra, bool *pending);
typedef void (*GucRealAssignHook) (double newval, void *extra);
typedef void (*GucStringAssignHook) (const char *newval, void *extra);
typedef void (*GucEnumAssignHook) (int newval, void *extra);
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index 799fa7ace68..c8300cffa8e 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -81,14 +81,14 @@ extern bool check_log_stats(bool *newval, void **extra, GucSource source);
extern bool check_log_timezone(char **newval, void **extra, GucSource source);
extern void assign_log_timezone(const char *newval, void *extra);
extern const char *show_log_timezone(void);
-extern void assign_maintenance_io_concurrency(int newval, void *extra);
-extern void assign_io_max_combine_limit(int newval, void *extra);
-extern void assign_io_combine_limit(int newval, void *extra);
+extern void assign_maintenance_io_concurrency(int newval, void *extra, bool *pending);
+extern void assign_io_max_combine_limit(int newval, void *extra, bool *pending);
+extern void assign_io_combine_limit(int newval, void *extra, bool *pending);
extern bool check_max_slot_wal_keep_size(int *newval, void **extra,
GucSource source);
-extern void assign_max_wal_size(int newval, void *extra);
+extern void assign_max_wal_size(int newval, void *extra, bool *pending);
extern bool check_max_stack_depth(int *newval, void **extra, GucSource source);
-extern void assign_max_stack_depth(int newval, void *extra);
+extern void assign_max_stack_depth(int newval, void *extra, bool *pending);
extern bool check_multixact_member_buffers(int *newval, void **extra,
GucSource source);
extern bool check_multixact_offset_buffers(int *newval, void **extra,
@@ -143,13 +143,13 @@ extern void assign_synchronous_standby_names(const char *newval, void *extra);
extern void assign_synchronous_commit(int newval, void *extra);
extern void assign_syslog_facility(int newval, void *extra);
extern void assign_syslog_ident(const char *newval, void *extra);
-extern void assign_tcp_keepalives_count(int newval, void *extra);
+extern void assign_tcp_keepalives_count(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_count(void);
-extern void assign_tcp_keepalives_idle(int newval, void *extra);
+extern void assign_tcp_keepalives_idle(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_idle(void);
-extern void assign_tcp_keepalives_interval(int newval, void *extra);
+extern void assign_tcp_keepalives_interval(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_interval(void);
-extern void assign_tcp_user_timeout(int newval, void *extra);
+extern void assign_tcp_user_timeout(int newval, void *extra, bool *pending);
extern const char *show_tcp_user_timeout(void);
extern bool check_temp_buffers(int *newval, void **extra, GucSource source);
extern bool check_temp_tablespaces(char **newval, void **extra,
@@ -165,7 +165,7 @@ extern bool check_transaction_buffers(int *newval, void **extra, GucSource sourc
extern bool check_transaction_deferrable(bool *newval, void **extra, GucSource source);
extern bool check_transaction_isolation(int *newval, void **extra, GucSource source);
extern bool check_transaction_read_only(bool *newval, void **extra, GucSource source);
-extern void assign_transaction_timeout(int newval, void *extra);
+extern void assign_transaction_timeout(int newval, void *extra, bool *pending);
extern const char *show_unix_socket_permissions(void);
extern bool check_wal_buffers(int *newval, void **extra, GucSource source);
extern bool check_wal_consistency_checking(char **newval, void **extra,
--
2.49.0
From efbe93b30e0174c4fba42047b14208b3fd5c0f43 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Fri, 4 Apr 2025 21:46:14 +0200
Subject: [PATCH v5 03/10] Introduce pss_barrierReceivedGeneration
Currently WaitForProcSignalBarrier allows to make sure the message sent
via EmitProcSignalBarrier was processed by all ProcSignal mechanism
participants.
Add pss_barrierReceivedGeneration alongside with pss_barrierGeneration,
which will be updated when a process has received the message, but not
processed it yet. This makes it possible to support a new mode of
waiting, when ProcSignal participants want to synchronize message
processing. To do that, a participant can wait via
WaitForProcSignalBarrierReceived when processing a message, effectively
making sure that all processes are going to start processing
ProcSignalBarrier simultaneously.
---
src/backend/storage/ipc/procsignal.c | 67 ++++++++++++++++++++++------
src/include/storage/procsignal.h | 1 +
2 files changed, 54 insertions(+), 14 deletions(-)
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index a9bb540b55a..c6bec9be423 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -58,7 +58,10 @@
* of it. For such use cases, we set a bit in pss_barrierCheckMask and then
* increment the current "barrier generation"; when the new barrier generation
* (or greater) appears in the pss_barrierGeneration flag of every process,
- * we know that the message has been received everywhere.
+ * we know that the message has been received and processed everywhere. In case
+ * if we only need to know only that the message was received everywhere (e.g.
+ * receiving processes need to handle the message in a coordinated fashion)
+ * use pss_barrierReceivedGeneration in the same way.
*/
typedef struct
{
@@ -70,6 +73,7 @@ typedef struct
/* Barrier-related fields (not protected by pss_mutex) */
pg_atomic_uint64 pss_barrierGeneration;
+ pg_atomic_uint64 pss_barrierReceivedGeneration;
pg_atomic_uint32 pss_barrierCheckMask;
ConditionVariable pss_barrierCV;
} ProcSignalSlot;
@@ -152,6 +156,8 @@ ProcSignalShmemInit(void)
slot->pss_cancel_key_len = 0;
MemSet(slot->pss_signalFlags, 0, sizeof(slot->pss_signalFlags));
pg_atomic_init_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
+ pg_atomic_init_u64(&slot->pss_barrierReceivedGeneration,
+ PG_UINT64_MAX);
pg_atomic_init_u32(&slot->pss_barrierCheckMask, 0);
ConditionVariableInit(&slot->pss_barrierCV);
}
@@ -199,6 +205,8 @@ ProcSignalInit(const uint8 *cancel_key, int cancel_key_len)
barrier_generation =
pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration);
pg_atomic_write_u64(&slot->pss_barrierGeneration, barrier_generation);
+ pg_atomic_write_u64(&slot->pss_barrierReceivedGeneration,
+ barrier_generation);
if (cancel_key_len > 0)
memcpy(slot->pss_cancel_key, cancel_key, cancel_key_len);
@@ -263,6 +271,7 @@ CleanupProcSignalState(int status, Datum arg)
* no barrier waits block on it.
*/
pg_atomic_write_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
+ pg_atomic_write_u64(&slot->pss_barrierReceivedGeneration, PG_UINT64_MAX);
SpinLockRelease(&slot->pss_mutex);
@@ -416,12 +425,8 @@ EmitProcSignalBarrier(ProcSignalBarrierType type)
return generation;
}
-/*
- * WaitForProcSignalBarrier - wait until it is guaranteed that all changes
- * requested by a specific call to EmitProcSignalBarrier() have taken effect.
- */
-void
-WaitForProcSignalBarrier(uint64 generation)
+static void
+WaitForProcSignalBarrierInternal(uint64 generation, bool receivedOnly)
{
Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));
@@ -436,12 +441,17 @@ WaitForProcSignalBarrier(uint64 generation)
uint64 oldval;
/*
- * It's important that we check only pss_barrierGeneration here and
- * not pss_barrierCheckMask. Bits in pss_barrierCheckMask get cleared
- * before the barrier is actually absorbed, but pss_barrierGeneration
+ * It's important that we check only pss_barrierGeneration &
+ * pss_barrierGeneration here and not pss_barrierCheckMask. Bits in
+ * pss_barrierCheckMask get cleared before the barrier is actually
+ * absorbed, but pss_barrierGeneration & pss_barrierReceivedGeneration
* is updated only afterward.
*/
- oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+ if (receivedOnly)
+ oldval = pg_atomic_read_u64(&slot->pss_barrierReceivedGeneration);
+ else
+ oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+
while (oldval < generation)
{
if (ConditionVariableTimedSleep(&slot->pss_barrierCV,
@@ -450,7 +460,11 @@ WaitForProcSignalBarrier(uint64 generation)
ereport(LOG,
(errmsg("still waiting for backend with PID %d to accept ProcSignalBarrier",
(int) pg_atomic_read_u32(&slot->pss_pid))));
- oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+
+ if (receivedOnly)
+ oldval = pg_atomic_read_u64(&slot->pss_barrierReceivedGeneration);
+ else
+ oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
}
ConditionVariableCancelSleep();
}
@@ -464,12 +478,33 @@ WaitForProcSignalBarrier(uint64 generation)
* The caller is probably calling this function because it wants to read
* the shared state or perform further writes to shared state once all
* backends are known to have absorbed the barrier. However, the read of
- * pss_barrierGeneration was performed unlocked; insert a memory barrier
- * to separate it from whatever follows.
+ * pss_barrierGeneration & pss_barrierReceivedGeneration was performed
+ * unlocked; insert a memory barrier to separate it from whatever follows.
*/
pg_memory_barrier();
}
+/*
+ * WaitForProcSignalBarrier - wait until it is guaranteed that all changes
+ * requested by a specific call to EmitProcSignalBarrier() have taken effect.
+ */
+void
+WaitForProcSignalBarrier(uint64 generation)
+{
+ WaitForProcSignalBarrierInternal(generation, false);
+}
+
+/*
+ * WaitForProcSignalBarrierReceived - wait until it is guaranteed that all
+ * backends have observed the message sent by a specific call to
+ * EmitProcSignalBarrier().
+ */
+void
+WaitForProcSignalBarrierReceived(uint64 generation)
+{
+ WaitForProcSignalBarrierInternal(generation, true);
+}
+
/*
* Handle receipt of an interrupt indicating a global barrier event.
*
@@ -523,6 +558,10 @@ ProcessProcSignalBarrier(void)
if (local_gen == shared_gen)
return;
+ /* The message is observed, record that */
+ pg_atomic_write_u64(&MyProcSignalSlot->pss_barrierReceivedGeneration,
+ shared_gen);
+
/*
* Get and clear the flags that are set for this backend. Note that
* pg_atomic_exchange_u32 is a full barrier, so we're guaranteed that the
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index afeeb1ca019..2733bbb8c5b 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -79,6 +79,7 @@ extern void SendCancelRequest(int backendPID, const uint8 *cancel_key, int cance
extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
extern void WaitForProcSignalBarrier(uint64 generation);
+extern void WaitForProcSignalBarrierReceived(uint64 generation);
extern void ProcessProcSignalBarrier(void);
extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
--
2.49.0
From a8e77ba00c05765f6d7ed05c8239a6bfecdbce4c Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Fri, 28 Feb 2025 19:54:47 +0100
Subject: [PATCH v5 04/10] Allow to use multiple shared memory mappings
Currently all the work with shared memory is done via a single anonymous
memory mapping, which limits ways how the shared memory could be organized.
Introduce possibility to allocate multiple shared memory mappings, where
a single mapping is associated with a specified shared memory segment.
There is only fixed amount of available segments, currently only one
main shared memory segment is allocated. A new shared memory API is
introduces, extended with a segment as a new parameter. As a path of
least resistance, the original API is kept in place, utilizing the main
shared memory segment.
---
src/backend/port/posix_sema.c | 4 +-
src/backend/port/sysv_sema.c | 4 +-
src/backend/port/sysv_shmem.c | 138 +++++++++++++++++++---------
src/backend/port/win32_sema.c | 2 +-
src/backend/storage/ipc/ipc.c | 4 +-
src/backend/storage/ipc/ipci.c | 63 +++++++------
src/backend/storage/ipc/shmem.c | 148 +++++++++++++++++++++---------
src/backend/storage/lmgr/lwlock.c | 13 ++-
src/include/storage/ipc.h | 2 +-
src/include/storage/pg_sema.h | 2 +-
src/include/storage/pg_shmem.h | 18 ++++
src/include/storage/shmem.h | 12 +++
12 files changed, 284 insertions(+), 126 deletions(-)
diff --git a/src/backend/port/posix_sema.c b/src/backend/port/posix_sema.c
index 269c7460817..401e1113fa1 100644
--- a/src/backend/port/posix_sema.c
+++ b/src/backend/port/posix_sema.c
@@ -193,7 +193,7 @@ PGSemaphoreShmemSize(int maxSemas)
* we don't have to expose the counters to other processes.)
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
struct stat statbuf;
@@ -220,7 +220,7 @@ PGReserveSemaphores(int maxSemas)
* ShmemAlloc() won't be ready yet.
*/
sharedSemas = (PGSemaphore)
- ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+ ShmemAllocUnlockedInSegment(PGSemaphoreShmemSize(maxSemas), shmem_segment);
#endif
numSems = 0;
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
index 423b2b4f9d6..4ce2cfb662b 100644
--- a/src/backend/port/sysv_sema.c
+++ b/src/backend/port/sysv_sema.c
@@ -307,7 +307,7 @@ PGSemaphoreShmemSize(int maxSemas)
* have clobbered.)
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
struct stat statbuf;
@@ -328,7 +328,7 @@ PGReserveSemaphores(int maxSemas)
* ShmemAlloc() won't be ready yet.
*/
sharedSemas = (PGSemaphore)
- ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+ ShmemAllocUnlockedInSegment(PGSemaphoreShmemSize(maxSemas), shmem_segment);
numSharedSemas = 0;
maxSharedSemas = maxSemas;
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 197926d44f6..56af0231d24 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -94,8 +94,19 @@ typedef enum
unsigned long UsedShmemSegID = 0;
void *UsedShmemSegAddr = NULL;
-static Size AnonymousShmemSize;
-static void *AnonymousShmem = NULL;
+typedef struct AnonymousMapping
+{
+ int shmem_segment;
+ Size shmem_size; /* Size of the mapping */
+ Pointer shmem; /* Pointer to the start of the mapped memory */
+ Pointer seg_addr; /* SysV shared memory for the header */
+ unsigned long seg_id; /* IPC key */
+} AnonymousMapping;
+
+static AnonymousMapping Mappings[ANON_MAPPINGS];
+
+/* Keeps track of used mapping segments */
+static int next_free_segment = 0;
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
@@ -104,6 +115,28 @@ static IpcMemoryState PGSharedMemoryAttach(IpcMemoryId shmId,
void *attachAt,
PGShmemHeader **addr);
+static const char*
+MappingName(int shmem_segment)
+{
+ switch (shmem_segment)
+ {
+ case MAIN_SHMEM_SEGMENT:
+ return "main";
+ default:
+ return "unknown";
+ }
+}
+
+static void
+DebugMappings()
+{
+ for(int i = 0; i < next_free_segment; i++)
+ {
+ AnonymousMapping m = Mappings[i];
+ elog(DEBUG1, "Mapping[%s]: addr %p, size %zu",
+ MappingName(i), m.shmem, m.shmem_size);
+ }
+}
/*
* InternalIpcMemoryCreate(memKey, size)
@@ -591,14 +624,13 @@ check_huge_page_size(int *newval, void **extra, GucSource source)
/*
* Creates an anonymous mmap()ed shared memory segment.
*
- * Pass the requested size in *size. This function will modify *size to the
- * actual size of the allocation, if it ends up allocating a segment that is
- * larger than requested.
+ * This function will modify mapping size to the actual size of the allocation,
+ * if it ends up allocating a segment that is larger than requested.
*/
-static void *
-CreateAnonymousSegment(Size *size)
+static void
+CreateAnonymousSegment(AnonymousMapping *mapping)
{
- Size allocsize = *size;
+ Size allocsize = mapping->shmem_size;
void *ptr = MAP_FAILED;
int mmap_errno = 0;
@@ -623,8 +655,11 @@ CreateAnonymousSegment(Size *size)
PG_MMAP_FLAGS | mmap_flags, -1, 0);
mmap_errno = errno;
if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
- elog(DEBUG1, "mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
- allocsize);
+ {
+ DebugMappings();
+ elog(DEBUG1, "segment[%s]: mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
+ MappingName(mapping->shmem_segment), allocsize);
+ }
}
#endif
@@ -642,7 +677,7 @@ CreateAnonymousSegment(Size *size)
* Use the original size, not the rounded-up value, when falling back
* to non-huge pages.
*/
- allocsize = *size;
+ allocsize = mapping->shmem_size;
ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
PG_MMAP_FLAGS, -1, 0);
mmap_errno = errno;
@@ -651,8 +686,10 @@ CreateAnonymousSegment(Size *size)
if (ptr == MAP_FAILED)
{
errno = mmap_errno;
+ DebugMappings();
ereport(FATAL,
- (errmsg("could not map anonymous shared memory: %m"),
+ (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment)),
(mmap_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request "
"for a shared memory segment exceeded available memory, "
@@ -663,8 +700,8 @@ CreateAnonymousSegment(Size *size)
allocsize) : 0));
}
- *size = allocsize;
- return ptr;
+ mapping->shmem = ptr;
+ mapping->shmem_size = allocsize;
}
/*
@@ -674,13 +711,18 @@ CreateAnonymousSegment(Size *size)
static void
AnonymousShmemDetach(int status, Datum arg)
{
- /* Release anonymous shared memory block, if any. */
- if (AnonymousShmem != NULL)
+ for(int i = 0; i < next_free_segment; i++)
{
- if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
- elog(LOG, "munmap(%p, %zu) failed: %m",
- AnonymousShmem, AnonymousShmemSize);
- AnonymousShmem = NULL;
+ AnonymousMapping m = Mappings[i];
+
+ /* Release anonymous shared memory block, if any. */
+ if (m.shmem != NULL)
+ {
+ if (munmap(m.shmem, m.shmem_size) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ m.shmem, m.shmem_size);
+ m.shmem = NULL;
+ }
}
}
@@ -705,6 +747,7 @@ PGSharedMemoryCreate(Size size,
PGShmemHeader *hdr;
struct stat statbuf;
Size sysvsize;
+ AnonymousMapping *mapping = &Mappings[next_free_segment];
/*
* We use the data directory's ID info (inode and device numbers) to
@@ -733,11 +776,15 @@ PGSharedMemoryCreate(Size size,
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+ mapping->shmem_size = size;
+ mapping->shmem_segment = next_free_segment;
if (shared_memory_type == SHMEM_TYPE_MMAP)
{
- AnonymousShmem = CreateAnonymousSegment(&size);
- AnonymousShmemSize = size;
+ /* On success, mapping data will be modified. */
+ CreateAnonymousSegment(mapping);
+
+ next_free_segment++;
/* Register on-exit routine to unmap the anonymous segment */
on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
@@ -760,7 +807,7 @@ PGSharedMemoryCreate(Size size,
* loop simultaneously. (CreateDataDirLockFile() does not entirely ensure
* that, but prefer fixing it over coping here.)
*/
- NextShmemSegID = statbuf.st_ino;
+ NextShmemSegID = statbuf.st_ino + next_free_segment;
for (;;)
{
@@ -852,13 +899,13 @@ PGSharedMemoryCreate(Size size,
/*
* Initialize space allocation status for segment.
*/
- hdr->totalsize = size;
+ hdr->totalsize = mapping->shmem_size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
*shim = hdr;
/* Save info for possible future use */
- UsedShmemSegAddr = memAddress;
- UsedShmemSegID = (unsigned long) NextShmemSegID;
+ mapping->seg_addr = memAddress;
+ mapping->seg_id = (unsigned long) NextShmemSegID;
/*
* If AnonymousShmem is NULL here, then we're not using anonymous shared
@@ -866,10 +913,10 @@ PGSharedMemoryCreate(Size size,
* block. Otherwise, the System V shared memory block is only a shim, and
* we must return a pointer to the real block.
*/
- if (AnonymousShmem == NULL)
+ if (mapping->shmem == NULL)
return hdr;
- memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
- return (PGShmemHeader *) AnonymousShmem;
+ memcpy(mapping->shmem, hdr, sizeof(PGShmemHeader));
+ return (PGShmemHeader *) mapping->shmem;
}
#ifdef EXEC_BACKEND
@@ -969,23 +1016,28 @@ PGSharedMemoryNoReAttach(void)
void
PGSharedMemoryDetach(void)
{
- if (UsedShmemSegAddr != NULL)
+ for(int i = 0; i < next_free_segment; i++)
{
- if ((shmdt(UsedShmemSegAddr) < 0)
+ AnonymousMapping m = Mappings[i];
+
+ if (m.seg_addr != NULL)
+ {
+ if ((shmdt(m.seg_addr) < 0)
#if defined(EXEC_BACKEND) && defined(__CYGWIN__)
- /* Work-around for cygipc exec bug */
- && shmdt(NULL) < 0
+ /* Work-around for cygipc exec bug */
+ && shmdt(NULL) < 0
#endif
- )
- elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
- UsedShmemSegAddr = NULL;
- }
+ )
+ elog(LOG, "shmdt(%p) failed: %m", m.seg_addr);
+ m.seg_addr = NULL;
+ }
- if (AnonymousShmem != NULL)
- {
- if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
- elog(LOG, "munmap(%p, %zu) failed: %m",
- AnonymousShmem, AnonymousShmemSize);
- AnonymousShmem = NULL;
+ if (m.shmem != NULL)
+ {
+ if (munmap(m.shmem, m.shmem_size) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ m.shmem, m.shmem_size);
+ m.shmem = NULL;
+ }
}
}
diff --git a/src/backend/port/win32_sema.c b/src/backend/port/win32_sema.c
index 5854ad1f54d..e7365ff8060 100644
--- a/src/backend/port/win32_sema.c
+++ b/src/backend/port/win32_sema.c
@@ -44,7 +44,7 @@ PGSemaphoreShmemSize(int maxSemas)
* process exits.
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
mySemSet = (HANDLE *) malloc(maxSemas * sizeof(HANDLE));
if (mySemSet == NULL)
diff --git a/src/backend/storage/ipc/ipc.c b/src/backend/storage/ipc/ipc.c
index 567739b5be9..5b55bec8d9d 100644
--- a/src/backend/storage/ipc/ipc.c
+++ b/src/backend/storage/ipc/ipc.c
@@ -61,6 +61,8 @@ static void proc_exit_prepare(int code);
* but provide some additional features we need --- in particular,
* we want to register callbacks to invoke when we are disconnecting
* from a broken shared-memory context but not exiting the postmaster.
+ * Maximum number of such exit callbacks depends on the number of shared
+ * segments.
*
* Callback functions can take zero, one, or two args: the first passed
* arg is the integer exitcode, the second is the Datum supplied when
@@ -68,7 +70,7 @@ static void proc_exit_prepare(int code);
* ----------------------------------------------------------------
*/
-#define MAX_ON_EXITS 20
+#define MAX_ON_EXITS 40
struct ONEXIT
{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2fa045e6b0f..8b38e985327 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -86,7 +86,7 @@ RequestAddinShmemSpace(Size size)
* required.
*/
Size
-CalculateShmemSize(int *num_semaphores)
+CalculateShmemSize(int *num_semaphores, int shmem_segment)
{
Size size;
int numSemas;
@@ -206,33 +206,38 @@ CreateSharedMemoryAndSemaphores(void)
Assert(!IsUnderPostmaster);
- /* Compute the size of the shared-memory block */
- size = CalculateShmemSize(&numSemas);
- elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
-
- /*
- * Create the shmem segment
- */
- seghdr = PGSharedMemoryCreate(size, &shim);
-
- /*
- * Make sure that huge pages are never reported as "unknown" while the
- * server is running.
- */
- Assert(strcmp("unknown",
- GetConfigOption("huge_pages_status", false, false)) != 0);
-
- InitShmemAccess(seghdr);
-
- /*
- * Create semaphores
- */
- PGReserveSemaphores(numSemas);
-
- /*
- * Set up shared memory allocation mechanism
- */
- InitShmemAllocation();
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ /* Compute the size of the shared-memory block */
+ size = CalculateShmemSize(&numSemas, segment);
+ elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
+
+ /*
+ * Create the shmem segment.
+ *
+ * XXX: Do multiple shims are needed, one per segment?
+ */
+ seghdr = PGSharedMemoryCreate(size, &shim);
+
+ /*
+ * Make sure that huge pages are never reported as "unknown" while the
+ * server is running.
+ */
+ Assert(strcmp("unknown",
+ GetConfigOption("huge_pages_status", false, false)) != 0);
+
+ InitShmemAccessInSegment(seghdr, segment);
+
+ /*
+ * Create semaphores
+ */
+ PGReserveSemaphores(numSemas, segment);
+
+ /*
+ * Set up shared memory allocation mechanism
+ */
+ InitShmemAllocationInSegment(segment);
+ }
/* Initialize subsystems */
CreateOrAttachShmemStructs();
@@ -363,7 +368,7 @@ InitializeShmemGUCs(void)
/*
* Calculate the shared memory size and round up to the nearest megabyte.
*/
- size_b = CalculateShmemSize(&num_semas);
+ size_b = CalculateShmemSize(&num_semas, MAIN_SHMEM_SEGMENT);
size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
sprintf(buf, "%zu", size_mb);
SetConfigOption("shared_memory_size", buf,
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index c9ae3b45b76..72255a1c5ca 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -76,19 +76,19 @@
#include "utils/builtins.h"
static void *ShmemAllocRaw(Size size, Size *allocated_size);
+static void *ShmemAllocRawInSegment(Size size, Size *allocated_size,
+ int shmem_segment);
/* shared memory global variables */
-static PGShmemHeader *ShmemSegHdr; /* shared mem segment header */
+ShmemSegment Segments[ANON_MAPPINGS];
-static void *ShmemBase; /* start address of shared memory */
-
-static void *ShmemEnd; /* end+1 address of shared memory */
-
-slock_t *ShmemLock; /* spinlock for shared memory and LWLock
- * allocation */
-
-static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */
+/*
+ * Primary index hashtable for shmem, for simplicity we use a single for all
+ * shared memory segments. There can be performance consequences of that, and
+ * an alternative option would be to have one index per shared memory segments.
+ */
+static HTAB *ShmemIndex = NULL;
/* To get reliable results for NUMA inquiry we need to "touch pages" once */
static bool firstNumaTouch = true;
@@ -101,9 +101,17 @@ Datum pg_numa_available(PG_FUNCTION_ARGS);
void
InitShmemAccess(PGShmemHeader *seghdr)
{
- ShmemSegHdr = seghdr;
- ShmemBase = seghdr;
- ShmemEnd = (char *) ShmemBase + seghdr->totalsize;
+ InitShmemAccessInSegment(seghdr, MAIN_SHMEM_SEGMENT);
+}
+
+void
+InitShmemAccessInSegment(PGShmemHeader *seghdr, int shmem_segment)
+{
+ PGShmemHeader *shmhdr = (PGShmemHeader *) seghdr;
+ ShmemSegment *seg = &Segments[shmem_segment];
+ seg->ShmemSegHdr = shmhdr;
+ seg->ShmemBase = (void *) shmhdr;
+ seg->ShmemEnd = (char *) seg->ShmemBase + shmhdr->totalsize;
}
/*
@@ -114,7 +122,13 @@ InitShmemAccess(PGShmemHeader *seghdr)
void
InitShmemAllocation(void)
{
- PGShmemHeader *shmhdr = ShmemSegHdr;
+ InitShmemAllocationInSegment(MAIN_SHMEM_SEGMENT);
+}
+
+void
+InitShmemAllocationInSegment(int shmem_segment)
+{
+ PGShmemHeader *shmhdr = Segments[shmem_segment].ShmemSegHdr;
char *aligned;
Assert(shmhdr != NULL);
@@ -123,9 +137,9 @@ InitShmemAllocation(void)
* Initialize the spinlock used by ShmemAlloc. We must use
* ShmemAllocUnlocked, since obviously ShmemAlloc can't be called yet.
*/
- ShmemLock = (slock_t *) ShmemAllocUnlocked(sizeof(slock_t));
+ Segments[shmem_segment].ShmemLock = (slock_t *) ShmemAllocUnlockedInSegment(sizeof(slock_t), shmem_segment);
- SpinLockInit(ShmemLock);
+ SpinLockInit(Segments[shmem_segment].ShmemLock);
/*
* Allocations after this point should go through ShmemAlloc, which
@@ -150,11 +164,17 @@ InitShmemAllocation(void)
*/
void *
ShmemAlloc(Size size)
+{
+ return ShmemAllocInSegment(size, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemAllocInSegment(Size size, int shmem_segment)
{
void *newSpace;
Size allocated_size;
- newSpace = ShmemAllocRaw(size, &allocated_size);
+ newSpace = ShmemAllocRawInSegment(size, &allocated_size, shmem_segment);
if (!newSpace)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -184,6 +204,12 @@ ShmemAllocNoError(Size size)
*/
static void *
ShmemAllocRaw(Size size, Size *allocated_size)
+{
+ return ShmemAllocRawInSegment(size, allocated_size, MAIN_SHMEM_SEGMENT);
+}
+
+static void *
+ShmemAllocRawInSegment(Size size, Size *allocated_size, int shmem_segment)
{
Size newStart;
Size newFree;
@@ -203,22 +229,22 @@ ShmemAllocRaw(Size size, Size *allocated_size)
size = CACHELINEALIGN(size);
*allocated_size = size;
- Assert(ShmemSegHdr != NULL);
+ Assert(Segments[shmem_segment].ShmemSegHdr != NULL);
- SpinLockAcquire(ShmemLock);
+ SpinLockAcquire(Segments[shmem_segment].ShmemLock);
- newStart = ShmemSegHdr->freeoffset;
+ newStart = Segments[shmem_segment].ShmemSegHdr->freeoffset;
newFree = newStart + size;
- if (newFree <= ShmemSegHdr->totalsize)
+ if (newFree <= Segments[shmem_segment].ShmemSegHdr->totalsize)
{
- newSpace = (char *) ShmemBase + newStart;
- ShmemSegHdr->freeoffset = newFree;
+ newSpace = (char *) Segments[shmem_segment].ShmemBase + newStart;
+ Segments[shmem_segment].ShmemSegHdr->freeoffset = newFree;
}
else
newSpace = NULL;
- SpinLockRelease(ShmemLock);
+ SpinLockRelease(Segments[shmem_segment].ShmemLock);
/* note this assert is okay with newSpace == NULL */
Assert(newSpace == (void *) CACHELINEALIGN(newSpace));
@@ -236,6 +262,12 @@ ShmemAllocRaw(Size size, Size *allocated_size)
*/
void *
ShmemAllocUnlocked(Size size)
+{
+ return ShmemAllocUnlockedInSegment(size, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemAllocUnlockedInSegment(Size size, int shmem_segment)
{
Size newStart;
Size newFree;
@@ -246,19 +278,19 @@ ShmemAllocUnlocked(Size size)
*/
size = MAXALIGN(size);
- Assert(ShmemSegHdr != NULL);
+ Assert(Segments[shmem_segment].ShmemSegHdr != NULL);
- newStart = ShmemSegHdr->freeoffset;
+ newStart = Segments[shmem_segment].ShmemSegHdr->freeoffset;
newFree = newStart + size;
- if (newFree > ShmemSegHdr->totalsize)
+ if (newFree > Segments[shmem_segment].ShmemSegHdr->totalsize)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of shared memory (%zu bytes requested)",
size)));
- ShmemSegHdr->freeoffset = newFree;
+ Segments[shmem_segment].ShmemSegHdr->freeoffset = newFree;
- newSpace = (char *) ShmemBase + newStart;
+ newSpace = (char *) Segments[shmem_segment].ShmemBase + newStart;
Assert(newSpace == (void *) MAXALIGN(newSpace));
@@ -273,7 +305,13 @@ ShmemAllocUnlocked(Size size)
bool
ShmemAddrIsValid(const void *addr)
{
- return (addr >= ShmemBase) && (addr < ShmemEnd);
+ return ShmemAddrIsValidInSegment(addr, MAIN_SHMEM_SEGMENT);
+}
+
+bool
+ShmemAddrIsValidInSegment(const void *addr, int shmem_segment)
+{
+ return (addr >= Segments[shmem_segment].ShmemBase) && (addr < Segments[shmem_segment].ShmemEnd);
}
/*
@@ -334,6 +372,18 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
long max_size, /* max size of the table */
HASHCTL *infoP, /* info about key and bucket size */
int hash_flags) /* info about infoP */
+{
+ return ShmemInitHashInSegment(name, init_size, max_size, infoP, hash_flags,
+ MAIN_SHMEM_SEGMENT);
+}
+
+HTAB *
+ShmemInitHashInSegment(const char *name, /* table string name for shmem index */
+ long init_size, /* initial table size */
+ long max_size, /* max size of the table */
+ HASHCTL *infoP, /* info about key and bucket size */
+ int hash_flags, /* info about infoP */
+ int shmem_segment) /* in which segment to keep the table */
{
bool found;
void *location;
@@ -350,9 +400,9 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE;
/* look it up in the shmem index */
- location = ShmemInitStruct(name,
+ location = ShmemInitStructInSegment(name,
hash_get_shared_size(infoP, hash_flags),
- &found);
+ &found, shmem_segment);
/*
* if it already exists, attach to it rather than allocate and initialize
@@ -385,6 +435,13 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
*/
void *
ShmemInitStruct(const char *name, Size size, bool *foundPtr)
+{
+ return ShmemInitStructInSegment(name, size, foundPtr, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemInitStructInSegment(const char *name, Size size, bool *foundPtr,
+ int shmem_segment)
{
ShmemIndexEnt *result;
void *structPtr;
@@ -393,7 +450,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
if (!ShmemIndex)
{
- PGShmemHeader *shmemseghdr = ShmemSegHdr;
+ PGShmemHeader *shmemseghdr = Segments[shmem_segment].ShmemSegHdr;
/* Must be trying to create/attach to ShmemIndex itself */
Assert(strcmp(name, "ShmemIndex") == 0);
@@ -416,7 +473,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
* process can be accessing shared memory yet.
*/
Assert(shmemseghdr->index == NULL);
- structPtr = ShmemAlloc(size);
+ structPtr = ShmemAllocInSegment(size, shmem_segment);
shmemseghdr->index = structPtr;
*foundPtr = false;
}
@@ -433,8 +490,8 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
LWLockRelease(ShmemIndexLock);
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("could not create ShmemIndex entry for data structure \"%s\"",
- name)));
+ errmsg("could not create ShmemIndex entry for data structure \"%s\" in segment %d",
+ name, shmem_segment)));
}
if (*foundPtr)
@@ -459,7 +516,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
Size allocated_size;
/* It isn't in the table yet. allocate and initialize it */
- structPtr = ShmemAllocRaw(size, &allocated_size);
+ structPtr = ShmemAllocRawInSegment(size, &allocated_size, shmem_segment);
if (structPtr == NULL)
{
/* out of memory; remove the failed ShmemIndex entry */
@@ -478,14 +535,13 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
LWLockRelease(ShmemIndexLock);
- Assert(ShmemAddrIsValid(structPtr));
+ Assert(ShmemAddrIsValidInSegment(structPtr, shmem_segment));
Assert(structPtr == (void *) CACHELINEALIGN(structPtr));
return structPtr;
}
-
/*
* Add two Size values, checking for overflow
*/
@@ -542,10 +598,11 @@ pg_get_shmem_allocations(PG_FUNCTION_ARGS)
/* output all allocated entries */
memset(nulls, 0, sizeof(nulls));
+ /* XXX: take all shared memory segments into account. */
while ((ent = (ShmemIndexEnt *) hash_seq_search(&hstat)) != NULL)
{
values[0] = CStringGetTextDatum(ent->key);
- values[1] = Int64GetDatum((char *) ent->location - (char *) ShmemSegHdr);
+ values[1] = Int64GetDatum((char *) ent->location - (char *) Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr);
values[2] = Int64GetDatum(ent->size);
values[3] = Int64GetDatum(ent->allocated_size);
named_allocated += ent->allocated_size;
@@ -557,15 +614,15 @@ pg_get_shmem_allocations(PG_FUNCTION_ARGS)
/* output shared memory allocated but not counted via the shmem index */
values[0] = CStringGetTextDatum("<anonymous>");
nulls[1] = true;
- values[2] = Int64GetDatum(ShmemSegHdr->freeoffset - named_allocated);
+ values[2] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset - named_allocated);
values[3] = values[2];
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
/* output as-of-yet unused shared memory */
nulls[0] = true;
- values[1] = Int64GetDatum(ShmemSegHdr->freeoffset);
+ values[1] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset);
nulls[1] = false;
- values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemSegHdr->freeoffset);
+ values[2] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->totalsize - Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset);
values[3] = values[2];
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
@@ -630,7 +687,12 @@ pg_get_shmem_allocations_numa(PG_FUNCTION_ARGS)
* this is not very likely, and moreover we have more entries, each of
* them using only fraction of the total pages.
*/
- shm_total_page_count = (ShmemSegHdr->totalsize / os_page_size) + 1;
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ PGShmemHeader *shmhdr = Segments[segment].ShmemSegHdr;
+ shm_total_page_count += (shmhdr->totalsize / os_page_size) + 1;
+ }
+
page_ptrs = palloc0(sizeof(void *) * shm_total_page_count);
pages_status = palloc(sizeof(int) * shm_total_page_count);
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 46f44bc4511..a36b08895c8 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -80,6 +80,8 @@
#include "pg_trace.h"
#include "pgstat.h"
#include "port/pg_bitutils.h"
+#include "postmaster/postmaster.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/proclist.h"
#include "storage/procnumber.h"
@@ -618,10 +620,15 @@ LWLockNewTrancheId(void)
int *LWLockCounter;
LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
- /* We use the ShmemLock spinlock to protect LWLockCounter */
- SpinLockAcquire(ShmemLock);
+ /*
+ * We use the ShmemLock spinlock to protect LWLockCounter.
+ *
+ * XXX: Looks like this is the only use of Segments outside of shmem.c,
+ * it's maybe worth it to reshape this part to hide Segments structure.
+ */
+ SpinLockAcquire(Segments[MAIN_SHMEM_SEGMENT].ShmemLock);
result = (*LWLockCounter)++;
- SpinLockRelease(ShmemLock);
+ SpinLockRelease(Segments[MAIN_SHMEM_SEGMENT].ShmemLock);
return result;
}
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 3baf418b3d1..6ebda479ced 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -77,7 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
/* ipci.c */
extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
-extern Size CalculateShmemSize(int *num_semaphores);
+extern Size CalculateShmemSize(int *num_semaphores, int shmem_segment);
extern void CreateSharedMemoryAndSemaphores(void);
#ifdef EXEC_BACKEND
extern void AttachSharedMemoryStructs(void);
diff --git a/src/include/storage/pg_sema.h b/src/include/storage/pg_sema.h
index fa6ca35a51f..8ae9637fcd0 100644
--- a/src/include/storage/pg_sema.h
+++ b/src/include/storage/pg_sema.h
@@ -41,7 +41,7 @@ typedef HANDLE PGSemaphore;
extern Size PGSemaphoreShmemSize(int maxSemas);
/* Module initialization (called during postmaster start or shmem reinit) */
-extern void PGReserveSemaphores(int maxSemas);
+extern void PGReserveSemaphores(int maxSemas, int shmem_segment);
/* Allocate a PGSemaphore structure with initial count 1 */
extern PGSemaphore PGSemaphoreCreate(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 5f7d4b83a60..2348c59b5a0 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -25,6 +25,7 @@
#define PG_SHMEM_H
#include "storage/dsm_impl.h"
+#include "storage/spin.h"
typedef struct PGShmemHeader /* standard header for all Postgres shmem */
{
@@ -41,6 +42,20 @@ typedef struct PGShmemHeader /* standard header for all Postgres shmem */
#endif
} PGShmemHeader;
+typedef struct ShmemSegment
+{
+ PGShmemHeader *ShmemSegHdr; /* shared mem segment header */
+ void *ShmemBase; /* start address of shared memory */
+ void *ShmemEnd; /* end+1 address of shared memory */
+ slock_t *ShmemLock; /* spinlock for shared memory and LWLock
+ * allocation */
+} ShmemSegment;
+
+/* Number of available segments for anonymous memory mappings */
+#define ANON_MAPPINGS 1
+
+extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
+
/* GUC variables */
extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
@@ -91,4 +106,7 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
+/* The main segment, contains everything except buffer blocks and related data. */
+#define MAIN_SHMEM_SEGMENT 0
+
#endif /* PG_SHMEM_H */
diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h
index c1f668ded95..69663d412c3 100644
--- a/src/include/storage/shmem.h
+++ b/src/include/storage/shmem.h
@@ -29,15 +29,27 @@
extern PGDLLIMPORT slock_t *ShmemLock;
struct PGShmemHeader; /* avoid including storage/pg_shmem.h here */
extern void InitShmemAccess(struct PGShmemHeader *seghdr);
+extern void InitShmemAccessInSegment(struct PGShmemHeader *seghdr,
+ int shmem_segment);
extern void InitShmemAllocation(void);
+extern void InitShmemAllocationInSegment(int shmem_segment);
extern void *ShmemAlloc(Size size);
+extern void *ShmemAllocInSegment(Size size, int shmem_segment);
extern void *ShmemAllocNoError(Size size);
extern void *ShmemAllocUnlocked(Size size);
+extern void *ShmemAllocUnlockedInSegment(Size size, int shmem_segment);
extern bool ShmemAddrIsValid(const void *addr);
+extern bool ShmemAddrIsValidInSegment(const void *addr, int shmem_segment);
extern void InitShmemIndex(void);
+extern void InitVariableShmemIndex(void);
extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size,
HASHCTL *infoP, int hash_flags);
+extern HTAB *ShmemInitHashInSegment(const char *name, long init_size,
+ long max_size, HASHCTL *infoP,
+ int hash_flags, int shmem_segment);
extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
+extern void *ShmemInitStructInSegment(const char *name, Size size,
+ bool *foundPtr, int shmem_segment);
extern Size add_size(Size s1, Size s2);
extern Size mul_size(Size s1, Size s2);
--
2.49.0
From 6238657ddb8c9e63d28a1a96712278f548d3292c Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 11:47:04 +0200
Subject: [PATCH v5 05/10] Address space reservation for shared memory
Currently the shared memory layout is designed to pack everything tight
together, leaving no space between mappings for resizing. Here is how it
looks like for one mapping in /proc/$PID/maps, /dev/zero represents the
anonymous shared memory we talk about:
00400000-00490000 /path/bin/postgres
...
012d9000-0133e000 [heap]
7f443a800000-7f470a800000 /dev/zero (deleted)
7f470a800000-7f471831d000 /usr/lib/locale/locale-archive
7f4718400000-7f4718401000 /usr/lib64/libstdc++.so.6.0.34
...
Make the layout more dynamic via splitting every shared memory segment
into two parts:
* An anonymous file, which actually contains shared memory content. Such
an anonymous file is created via memfd_create, it lives in memory,
behaves like a regular file and semantically equivalent to an
anonymous memory allocated via mmap with MAP_ANONYMOUS.
* A reservation mapping, which size is much larger than required shared
segment size. This mapping is created with flags PROT_NONE (which
makes sure the reserved space is not used), and MAP_NORESERVE (to not
count the reserved space against memory limits). The anonymous file is
mapped into this reservation mapping.
The resulting layout looks like this:
00400000-00490000 /path/bin/postgres
...
3f526000-3f590000 rw-p [heap]
7fbd827fe000-7fbd8bdde000 rw-s /memfd:main (deleted) -- anon file
7fbd8bdde000-7fbe82800000 ---s /memfd:main (deleted) -- reservation
7fbe82800000-7fbe90670000 r--p /usr/lib/locale/locale-archive
7fbe90800000-7fbe90941000 r-xp /usr/lib64/libstdc++.so.6.0.34
To resize a shared memory segment in this layout it's possible to use ftruncate
on the anonymous file, adjusting access permissions on the reserved space as
needed.
This approach also do not impact the actual memory usage as reported by
the kernel. Here is the output of /proc/$PID/status for the master
version with shared_buffers = 128 MB:
// Peak virtual memory size, which is described as total pages
// mapped in mm_struct. It corresponds to the mapped reserved space
// and is the only number that grows with it.
VmPeak: 2043192 kB
// Size of memory portions. It contains RssAnon + RssFile + RssShmem
VmRSS: 22908 kB
// Size of resident anonymous memory
RssAnon: 768 kB
// Size of resident file mappings
RssFile: 10364 kB
// Size of resident shmem memory (includes SysV shm, mapping of tmpfs and
// shared anonymous mappings)
RssShmem: 11776 kB
Here is the same for the patch when reserving 20GB of space:
VmPeak: 21255824 kB
VmRSS: 25020 kB
RssAnon: 768 kB
RssFile: 10812 kB
RssShmem: 13440 kB
Cgroup v2 doesn't have any problems with that as well. To verify a new cgroup
was created with the memory limit 256 MB, then PostgreSQL was launched withing
this cgroup with shared_buffers = 128 MB:
$ cd /sys/fs/cgroup
$ mkdir postgres
$ cd postres
$ echo 268435456 > memory.max
$ echo $MASTER_PID_SHELL > cgroup.procs
# postgres from the master branch has being successfully launched
# from that shell
$ cat memory.current
17465344 (~16.6 MB)
# stop postgres
$ echo $PATCH_PID_SHELL > cgroup.procs
# postgres from the patch has being successfully launched from that shell
$ cat memory.current
20770816 (~19.8 MB)
To control the amount of space reserved a new GUC max_available_memory
is introduced. Ideally it should be based on the maximum available
memory, hense the name.
There are also few unrelated advantages of using anon files:
* We've got a file descriptor, which could be used for regular file
operations (modification, truncation, you name it).
* The file could be given a name, which improves readability when it
comes to process maps.
* By default, Linux will not add file-backed shared mappings into a core dump,
making it more convenient to work with them in PostgreSQL: no more huge dumps
to process.
The downside is that memfd_create is Linux specific.
---
src/backend/port/sysv_shmem.c | 290 ++++++++++++++++++++++------
src/backend/port/win32_shmem.c | 2 +-
src/backend/storage/ipc/ipci.c | 5 +-
src/backend/storage/ipc/shmem.c | 2 +-
src/backend/utils/init/globals.c | 1 +
src/backend/utils/misc/guc_tables.c | 14 ++
src/include/miscadmin.h | 1 +
src/include/portability/mem.h | 2 +-
src/include/storage/pg_shmem.h | 5 +-
9 files changed, 262 insertions(+), 60 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 56af0231d24..363ddfd1fca 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -97,10 +97,12 @@ void *UsedShmemSegAddr = NULL;
typedef struct AnonymousMapping
{
int shmem_segment;
- Size shmem_size; /* Size of the mapping */
+ Size shmem_size; /* Size of the actually used memory */
+ Size shmem_reserved; /* Size of the reserved mapping */
Pointer shmem; /* Pointer to the start of the mapped memory */
Pointer seg_addr; /* SysV shared memory for the header */
unsigned long seg_id; /* IPC key */
+ int segment_fd; /* fd for the backing anon file */
} AnonymousMapping;
static AnonymousMapping Mappings[ANON_MAPPINGS];
@@ -108,6 +110,49 @@ static AnonymousMapping Mappings[ANON_MAPPINGS];
/* Keeps track of used mapping segments */
static int next_free_segment = 0;
+/*
+ * Anonymous mapping layout we use looks like this:
+ *
+ * 00400000-00c2a000 r-xp /bin/postgres
+ * ...
+ * 3f526000-3f590000 rw-p [heap]
+ * 7fbd827fe000-7fbd8bdde000 rw-s /memfd:main (deleted)
+ * 7fbd8bdde000-7fbe82800000 ---s /memfd:main (deleted)
+ * 7fbe82800000-7fbe90670000 r--p /usr/lib/locale/locale-archive
+ * 7fbe90800000-7fbe90941000 r-xp /usr/lib64/libstdc++.so.6.0.34
+ * ...
+ *
+ * We need to place shared memory mappings in such a way, that there will be
+ * gaps between them in the address space. Those gaps have to be large enough
+ * to resize the mapping up to certain size, without counting towards the total
+ * memory consumption.
+ *
+ * To achieve this, for each shared memory segment we first create an anonymous
+ * file of specified size using memfd_create, which will accomodate actual
+ * shared memory mapping content. It is represented by the first /memfd:main
+ * with rw permissions. Then we create a mapping for this file using mmap, with
+ * size much larger than required and flags PROT_NONE (allows to make sure the
+ * reserved space will not be used) and MAP_NORESERVE (prevents the space from
+ * being counted against memory limits). The mapping serves as an address space
+ * reservation, into which shared memory segment can be extended and is
+ * represented by the second /memfd:main with no permissions.
+ *
+ * The reserved space for each segment is calculated as a fraction of the total
+ * reserved space (MaxAvailableMemory), as specified in the SHMEM_RESIZE_RATIO
+ * array.
+ */
+static double SHMEM_RESIZE_RATIO[1] = {
+ 1.0, /* MAIN_SHMEM_SLOT */
+};
+
+/*
+ * Flag telling that we have decided to use huge pages.
+ *
+ * XXX: It's possible to use GetConfigOption("huge_pages_status", false, false)
+ * instead, but it feels like an overkill.
+ */
+static bool huge_pages_on = false;
+
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
@@ -503,19 +548,20 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
* hugepage sizes, we might want to think about more invasive strategies,
* such as increasing shared_buffers to absorb the extra space.
*
- * Returns the (real, assumed or config provided) page size into
- * *hugepagesize, and the hugepage-related mmap flags to use into
- * *mmap_flags if requested by the caller. If huge pages are not supported,
- * *hugepagesize and *mmap_flags are set to 0.
+ * Returns the (real, assumed or config provided) page size into *hugepagesize,
+ * the hugepage-related mmap and memfd flags to use into *mmap_flags and
+ * *memfd_flags if requested by the caller. If huge pages are not supported,
+ * *hugepagesize, *mmap_flags and *memfd_flags are set to 0.
*/
void
-GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+GetHugePageSize(Size *hugepagesize, int *mmap_flags, int *memfd_flags)
{
#ifdef MAP_HUGETLB
Size default_hugepagesize = 0;
Size hugepagesize_local = 0;
int mmap_flags_local = 0;
+ int memfd_flags_local = 0;
/*
* System-dependent code to find out the default huge page size.
@@ -574,6 +620,7 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
}
mmap_flags_local = MAP_HUGETLB;
+ memfd_flags_local = MFD_HUGETLB;
/*
* On recent enough Linux, also include the explicit page size, if
@@ -584,7 +631,16 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
{
int shift = pg_ceil_log2_64(hugepagesize_local);
- mmap_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
+ memfd_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
+ }
+#endif
+
+#if defined(MFD_HUGE_MASK) && defined(MFD_HUGE_SHIFT)
+ if (hugepagesize_local != default_hugepagesize)
+ {
+ int shift = pg_ceil_log2_64(hugepagesize_local);
+
+ memfd_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
}
#endif
@@ -593,6 +649,8 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
*mmap_flags = mmap_flags_local;
if (hugepagesize)
*hugepagesize = hugepagesize_local;
+ if (memfd_flags)
+ *memfd_flags = memfd_flags_local;
#else
@@ -600,6 +658,8 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
*hugepagesize = 0;
if (mmap_flags)
*mmap_flags = 0;
+ if (memfd_flags)
+ *memfd_flags = 0;
#endif /* MAP_HUGETLB */
}
@@ -625,72 +685,90 @@ check_huge_page_size(int *newval, void **extra, GucSource source)
* Creates an anonymous mmap()ed shared memory segment.
*
* This function will modify mapping size to the actual size of the allocation,
- * if it ends up allocating a segment that is larger than requested.
+ * if it ends up allocating a segment that is larger than requested. If needed,
+ * it also rounds up the mapping reserved size to be a multiple of huge page
+ * size.
+ *
+ * Note that we do not fallback from huge pages to regular pages in this
+ * function, this decision was already made in ReserveAnonymousMemory and we
+ * stick to it.
*/
static void
CreateAnonymousSegment(AnonymousMapping *mapping)
{
Size allocsize = mapping->shmem_size;
void *ptr = MAP_FAILED;
- int mmap_errno = 0;
+ int save_errno = 0;
+ int mmap_flags = PG_MMAP_FLAGS, memfd_flags = 0;
+
+ elog(DEBUG1, "segment[%s]: size %zu, reserved %zu",
+ MappingName(mapping->shmem_segment), mapping->shmem_size,
+ mapping->shmem_reserved);
#ifndef MAP_HUGETLB
- /* PGSharedMemoryCreate should have dealt with this case */
- Assert(huge_pages != HUGE_PAGES_ON);
+ /* PrepareHugePages should have dealt with this case */
+ Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
#else
- if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ if (huge_pages_on)
{
- /*
- * Round up the request size to a suitable large value.
- */
Size hugepagesize;
- int mmap_flags;
- GetHugePageSize(&hugepagesize, &mmap_flags);
+ /* Make sure nothing is messed up */
+ Assert(huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY);
+
+ /* Round up the request size to a suitable large value */
+ GetHugePageSize(&hugepagesize, &mmap_flags, &memfd_flags);
if (allocsize % hugepagesize != 0)
allocsize += hugepagesize - (allocsize % hugepagesize);
- ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
- PG_MMAP_FLAGS | mmap_flags, -1, 0);
- mmap_errno = errno;
- if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
- {
- DebugMappings();
- elog(DEBUG1, "segment[%s]: mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
- MappingName(mapping->shmem_segment), allocsize);
- }
+ /*
+ * The reserved space is multiple of BLCKSZ. We know the huge page
+ * size, round up the reserved space to it.
+ */
+ mapping->shmem_reserved = mapping->shmem_reserved + hugepagesize -
+ (mapping->shmem_reserved % hugepagesize);
+
+ /* Verify that the new size is withing the reserved boundaries */
+ if (mapping->shmem_reserved < mapping->shmem_size)
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+ errmsg("not enough shared memory is reserved"),
+ errhint("You may need to increase \"max_available_memory\".")));
+
+ mmap_flags = PG_MMAP_FLAGS | mmap_flags;
}
#endif
/*
- * Report whether huge pages are in use. This needs to be tracked before
- * the second mmap() call if attempting to use huge pages failed
- * previously.
+ * Prepare an anonymous file backing the segment. Its size will be
+ * specified later via ftruncate.
+ *
+ * The file behaves like a regular file, but lives in memory. Once all
+ * references to the file are dropped, it is automatically released.
+ * Anonymous memory is used for all backing pages of the file, thus it has
+ * the same semantics as anonymous memory allocations using mmap with the
+ * MAP_ANONYMOUS flag.
*/
- SetConfigOption("huge_pages_status", (ptr == MAP_FAILED) ? "off" : "on",
- PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+ mapping->segment_fd = memfd_create(MappingName(mapping->shmem_segment),
+ memfd_flags);
- if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
+ /*
+ * Specify the segment file size using allocsize, which contains
+ * potentially modified value.
+ */
+ if(ftruncate(mapping->segment_fd, allocsize) == -1)
{
- /*
- * Use the original size, not the rounded-up value, when falling back
- * to non-huge pages.
- */
- allocsize = mapping->shmem_size;
- ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
- PG_MMAP_FLAGS, -1, 0);
- mmap_errno = errno;
- }
+ save_errno = errno;
- if (ptr == MAP_FAILED)
- {
- errno = mmap_errno;
DebugMappings();
+ close(mapping->segment_fd);
+
+ errno = save_errno;
ereport(FATAL,
- (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ (errmsg("segment[%s]: could not truncate anonymous file: %m",
MappingName(mapping->shmem_segment)),
- (mmap_errno == ENOMEM) ?
+ (save_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request "
"for a shared memory segment exceeded available memory, "
"swap space, or huge pages. To reduce the request size "
@@ -700,10 +778,112 @@ CreateAnonymousSegment(AnonymousMapping *mapping)
allocsize) : 0));
}
+ elog(DEBUG1, "segment[%s]: mmap(%zu)",
+ MappingName(mapping->shmem_segment), allocsize);
+
+ /*
+ * Create a reservation mapping.
+ */
+ ptr = mmap(NULL, mapping->shmem_reserved, PROT_NONE,
+ mmap_flags | MAP_NORESERVE, mapping->segment_fd, 0);
+ save_errno = errno;
+
+ if (ptr == MAP_FAILED)
+ {
+ DebugMappings();
+
+ errno = save_errno;
+ ereport(FATAL,
+ (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment))));
+ }
+
+ /* Make the memory accessible */
+ if(mprotect(ptr, allocsize, PROT_READ | PROT_WRITE) == -1)
+ {
+ save_errno = errno;
+ DebugMappings();
+
+ errno = save_errno;
+ ereport(FATAL,
+ (errmsg("segment[%s]: could not mprotect anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment))));
+ }
+
mapping->shmem = ptr;
mapping->shmem_size = allocsize;
}
+/*
+ * PrepareHugePages
+ *
+ * Figure out if there are enough huge pages to allocate all shared memory
+ * segments, and report that information via huge_pages_status and
+ * huge_pages_on. It needs to be called before creating shared memory segments.
+ *
+ * It is necessary to maintain the same semantic (simple on/off) for
+ * huge_pages_status, even if there are multiple shared memory segments: all
+ * segments either use huge pages or not, there is no mix of segments with
+ * different page size. The latter might be actually beneficial, in particular
+ * because only some segments may require large amount of memory, but for now
+ * we go with a simple solution.
+ */
+void
+PrepareHugePages()
+{
+ void *ptr = MAP_FAILED;
+
+ /* Reset to handle reinitialization */
+ next_free_segment = 0;
+
+ /* Complain if hugepages demanded but we can't possibly support them */
+#if !defined(MAP_HUGETLB)
+ if (huge_pages == HUGE_PAGES_ON)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("huge pages not supported on this platform")));
+#else
+ if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ {
+ Size hugepagesize, total_size = 0;
+ int mmap_flags;
+
+ GetHugePageSize(&hugepagesize, &mmap_flags, NULL);
+
+ /*
+ * Figure out how much memory is needed for all segments, keeping in
+ * mind that for every segment this value will be rounding up by the
+ * huge page size. The resulting value will be used to probe memory and
+ * decide whether we will allocate huge pages or not.
+ */
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ int numSemas;
+ Size segment_size = CalculateShmemSize(&numSemas, segment);
+
+ if (segment_size % hugepagesize != 0)
+ segment_size += hugepagesize - (segment_size % hugepagesize);
+
+ total_size += segment_size;
+ }
+
+ /* Map total amount of memory to test its availability. */
+ elog(DEBUG1, "reserving space: probe mmap(%zu) with MAP_HUGETLB",
+ total_size);
+ ptr = mmap(NULL, total_size, PROT_NONE,
+ PG_MMAP_FLAGS | MAP_ANONYMOUS | mmap_flags, -1, 0);
+ }
+#endif
+
+ /*
+ * Report whether huge pages are in use. This needs to be tracked before
+ * creating shared memory segments.
+ */
+ SetConfigOption("huge_pages_status", (ptr == MAP_FAILED) ? "off" : "on",
+ PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+ huge_pages_on = ptr != MAP_FAILED;
+}
+
/*
* AnonymousShmemDetach --- detach from an anonymous mmap'd block
* (called as an on_shmem_exit callback, hence funny argument list)
@@ -746,7 +926,7 @@ PGSharedMemoryCreate(Size size,
void *memAddress;
PGShmemHeader *hdr;
struct stat statbuf;
- Size sysvsize;
+ Size sysvsize, total_reserved;
AnonymousMapping *mapping = &Mappings[next_free_segment];
/*
@@ -760,14 +940,6 @@ PGSharedMemoryCreate(Size size,
errmsg("could not stat data directory \"%s\": %m",
DataDir)));
- /* Complain if hugepages demanded but we can't possibly support them */
-#if !defined(MAP_HUGETLB)
- if (huge_pages == HUGE_PAGES_ON)
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("huge pages not supported on this platform")));
-#endif
-
/* For now, we don't support huge pages in SysV memory */
if (huge_pages == HUGE_PAGES_ON && shared_memory_type != SHMEM_TYPE_MMAP)
ereport(ERROR,
@@ -776,8 +948,16 @@ PGSharedMemoryCreate(Size size,
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+
+ /* Prepare the mapping information */
mapping->shmem_size = size;
mapping->shmem_segment = next_free_segment;
+ total_reserved = (Size) MaxAvailableMemory * BLCKSZ;
+ mapping->shmem_reserved = total_reserved * SHMEM_RESIZE_RATIO[next_free_segment];
+
+ /* Round up to be a multiple of BLCKSZ */
+ mapping->shmem_reserved = mapping->shmem_reserved + BLCKSZ -
+ (mapping->shmem_reserved % BLCKSZ);
if (shared_memory_type == SHMEM_TYPE_MMAP)
{
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index 4dee856d6bd..732fedee87e 100644
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -627,7 +627,7 @@ pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
* use GetLargePageMinimum() instead.
*/
void
-GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+GetHugePageSize(Size *hugepagesize, int *mmap_flags, int *memfd_flags)
{
if (hugepagesize)
*hugepagesize = 0;
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 8b38e985327..b60f7ef9ce2 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -206,6 +206,9 @@ CreateSharedMemoryAndSemaphores(void)
Assert(!IsUnderPostmaster);
+ /* Decide if we use huge pages or regular size pages */
+ PrepareHugePages();
+
for(int segment = 0; segment < ANON_MAPPINGS; segment++)
{
/* Compute the size of the shared-memory block */
@@ -377,7 +380,7 @@ InitializeShmemGUCs(void)
/*
* Calculate the number of huge pages required.
*/
- GetHugePageSize(&hp_size, NULL);
+ GetHugePageSize(&hp_size, NULL, NULL);
if (hp_size != 0)
{
Size hp_required;
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 72255a1c5ca..8d025f0e907 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -817,7 +817,7 @@ pg_get_shmem_pagesize(void)
Assert(huge_pages_status != HUGE_PAGES_UNKNOWN);
if (huge_pages_status == HUGE_PAGES_ON)
- GetHugePageSize(&os_page_size, NULL);
+ GetHugePageSize(&os_page_size, NULL, NULL);
return os_page_size;
}
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index d31cb45a058..90d3feb547c 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -140,6 +140,7 @@ int max_parallel_maintenance_workers = 2;
* register background workers.
*/
int NBuffers = 16384;
+int MaxAvailableMemory = 524288;
int MaxConnections = 100;
int max_worker_processes = 8;
int max_parallel_workers = 8;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f04bfedb2fd..a221e446d6a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2376,6 +2376,20 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"max_available_memory", PGC_SIGHUP, RESOURCES_MEM,
+ gettext_noop("Sets the upper limit for the shared_buffers value."),
+ gettext_noop("Shared memory could be resized at runtime, this "
+ "parameters sets the upper limit for it, beyond which "
+ "resizing would not be supported. Normally this value "
+ "would be the same as the total available memory."),
+ GUC_UNIT_BLOCKS
+ },
+ &MaxAvailableMemory,
+ 524288, 16, INT_MAX / 2,
+ NULL, NULL, NULL
+ },
+
{
{"vacuum_buffer_usage_limit", PGC_USERSET, RESOURCES_MEM,
gettext_noop("Sets the buffer pool size for VACUUM, ANALYZE, and autovacuum."),
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 1bef98471c3..a0c37a7749e 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -173,6 +173,7 @@ extern PGDLLIMPORT char *DataDir;
extern PGDLLIMPORT int data_directory_mode;
extern PGDLLIMPORT int NBuffers;
+extern PGDLLIMPORT int MaxAvailableMemory;
extern PGDLLIMPORT int MaxBackends;
extern PGDLLIMPORT int MaxConnections;
extern PGDLLIMPORT int max_worker_processes;
diff --git a/src/include/portability/mem.h b/src/include/portability/mem.h
index ef9800732d9..40588ff6968 100644
--- a/src/include/portability/mem.h
+++ b/src/include/portability/mem.h
@@ -38,7 +38,7 @@
#define MAP_NOSYNC 0
#endif
-#define PG_MMAP_FLAGS (MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
+#define PG_MMAP_FLAGS (MAP_SHARED|MAP_HASSEMAPHORE)
/* Some really old systems don't define MAP_FAILED. */
#ifndef MAP_FAILED
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 2348c59b5a0..79b0b1ef9eb 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -61,6 +61,7 @@ extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
extern PGDLLIMPORT int huge_page_size;
extern PGDLLIMPORT int huge_pages_status;
+extern PGDLLIMPORT int MaxAvailableMemory;
/* Possible values for huge_pages and huge_pages_status */
typedef enum
@@ -104,7 +105,9 @@ extern PGShmemHeader *PGSharedMemoryCreate(Size size,
PGShmemHeader **shim);
extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
-extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
+extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
+ int *memfd_flags);
+void PrepareHugePages(void);
/* The main segment, contains everything except buffer blocks and related data. */
#define MAIN_SHMEM_SEGMENT 0
--
2.49.0
From f23d42ef1ccdb28b751a8f12c7737002def4e674 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 11:22:02 +0200
Subject: [PATCH v5 06/10] Introduce multiple shmem segments for shared buffers
Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status
Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.
There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
src/backend/port/sysv_shmem.c | 24 +++++++-
src/backend/storage/buffer/buf_init.c | 79 +++++++++++++++++---------
src/backend/storage/buffer/buf_table.c | 6 +-
src/backend/storage/buffer/freelist.c | 5 +-
src/backend/storage/ipc/ipci.c | 2 +-
src/include/storage/bufmgr.h | 2 +-
src/include/storage/pg_shmem.h | 24 +++++++-
7 files changed, 105 insertions(+), 37 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 363ddfd1fca..dac011b766b 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -139,10 +139,18 @@ static int next_free_segment = 0;
*
* The reserved space for each segment is calculated as a fraction of the total
* reserved space (MaxAvailableMemory), as specified in the SHMEM_RESIZE_RATIO
- * array.
+ * array. E.g. we allow BUFFERS_SHMEM_SEGMENT to take up to 60% of the whole
+ * space when resizing, based on the fact that it most likely will be the main
+ * consumer of this memory. Those numbers are pulled out of thin air for now,
+ * makes sense to evaluate them more precise.
*/
-static double SHMEM_RESIZE_RATIO[1] = {
- 1.0, /* MAIN_SHMEM_SLOT */
+static double SHMEM_RESIZE_RATIO[6] = {
+ 0.1, /* MAIN_SHMEM_SEGMENT */
+ 0.6, /* BUFFERS_SHMEM_SEGMENT */
+ 0.1, /* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+ 0.1, /* BUFFER_IOCV_SHMEM_SEGMENT */
+ 0.05, /* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+ 0.05, /* STRATEGY_SHMEM_SEGMENT */
};
/*
@@ -167,6 +175,16 @@ MappingName(int shmem_segment)
{
case MAIN_SHMEM_SEGMENT:
return "main";
+ case BUFFERS_SHMEM_SEGMENT:
+ return "buffers";
+ case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+ return "descriptors";
+ case BUFFER_IOCV_SHMEM_SEGMENT:
+ return "iocv";
+ case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+ return "checkpoint";
+ case STRATEGY_SHMEM_SEGMENT:
+ return "strategy";
default:
return "unknown";
}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1dc488a42..bd68b69ee98 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -62,7 +62,10 @@ CkptSortItem *CkptBufferIds;
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
*/
void
BufferManagerShmemInit(void)
@@ -74,22 +77,22 @@ BufferManagerShmemInit(void)
/* Align descriptors to a cacheline boundary. */
BufferDescriptors = (BufferDescPadded *)
- ShmemInitStruct("Buffer Descriptors",
+ ShmemInitStructInSegment("Buffer Descriptors",
NBuffers * sizeof(BufferDescPadded),
- &foundDescs);
+ &foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
/* Align buffer pool on IO page size boundary. */
BufferBlocks = (char *)
TYPEALIGN(PG_IO_ALIGN_SIZE,
- ShmemInitStruct("Buffer Blocks",
+ ShmemInitStructInSegment("Buffer Blocks",
NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
- &foundBufs));
+ &foundBufs, BUFFERS_SHMEM_SEGMENT));
/* Align condition variables to cacheline boundary. */
BufferIOCVArray = (ConditionVariableMinimallyPadded *)
- ShmemInitStruct("Buffer IO Condition Variables",
+ ShmemInitStructInSegment("Buffer IO Condition Variables",
NBuffers * sizeof(ConditionVariableMinimallyPadded),
- &foundIOCV);
+ &foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
/*
* The array used to sort to-be-checkpointed buffer ids is located in
@@ -99,8 +102,9 @@ BufferManagerShmemInit(void)
* painful.
*/
CkptBufferIds = (CkptSortItem *)
- ShmemInitStruct("Checkpoint BufferIds",
- NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+ ShmemInitStructInSegment("Checkpoint BufferIds",
+ NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+ CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
{
@@ -156,33 +160,54 @@ BufferManagerShmemInit(void)
* BufferManagerShmemSize
*
* compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
*/
Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
{
Size size = 0;
- /* size of buffer descriptors */
- size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
- /* to allow aligning buffer descriptors */
- size = add_size(size, PG_CACHE_LINE_SIZE);
+ if (shmem_segment == MAIN_SHMEM_SEGMENT)
+ return size;
- /* size of data pages, plus alignment padding */
- size = add_size(size, PG_IO_ALIGN_SIZE);
- size = add_size(size, mul_size(NBuffers, BLCKSZ));
+ if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+ {
+ /* size of buffer descriptors */
+ size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+ /* to allow aligning buffer descriptors */
+ size = add_size(size, PG_CACHE_LINE_SIZE);
+ }
- /* size of stuff controlled by freelist.c */
- size = add_size(size, StrategyShmemSize());
+ if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+ {
+ /* size of data pages, plus alignment padding */
+ size = add_size(size, PG_IO_ALIGN_SIZE);
+ size = add_size(size, mul_size(NBuffers, BLCKSZ));
+ }
- /* size of I/O condition variables */
- size = add_size(size, mul_size(NBuffers,
- sizeof(ConditionVariableMinimallyPadded)));
- /* to allow aligning the above */
- size = add_size(size, PG_CACHE_LINE_SIZE);
+ if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+ {
+ /* size of stuff controlled by freelist.c */
+ size = add_size(size, StrategyShmemSize());
+ }
- /* size of checkpoint sort array in bufmgr.c */
- size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+ if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+ {
+ /* size of I/O condition variables */
+ size = add_size(size, mul_size(NBuffers,
+ sizeof(ConditionVariableMinimallyPadded)));
+ /* to allow aligning the above */
+ size = add_size(size, PG_CACHE_LINE_SIZE);
+ }
+
+ if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+ {
+ /* size of checkpoint sort array in bufmgr.c */
+ size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+ }
return size;
}
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..a9952b36eba 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -22,6 +22,7 @@
#include "postgres.h"
#include "storage/buf_internals.h"
+#include "storage/pg_shmem.h"
/* entry for buffer lookup hashtable */
typedef struct
@@ -59,10 +60,11 @@ InitBufTable(int size)
info.entrysize = sizeof(BufferLookupEnt);
info.num_partitions = NUM_BUFFER_PARTITIONS;
- SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+ SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
size, size,
&info,
- HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+ HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+ STRATEGY_SHMEM_SEGMENT);
}
/*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 01909be0272..bd390f2709d 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -19,6 +19,7 @@
#include "port/atomics.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#define INT_ACCESS_ONCE(var) ((int)(*((volatile int *)&(var))))
@@ -491,9 +492,9 @@ StrategyInitialize(bool init)
* Get or create the shared strategy control block
*/
StrategyControl = (BufferStrategyControl *)
- ShmemInitStruct("Buffer Strategy Status",
+ ShmemInitStructInSegment("Buffer Strategy Status",
sizeof(BufferStrategyControl),
- &found);
+ &found, STRATEGY_SHMEM_SEGMENT);
if (!found)
{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index b60f7ef9ce2..2dbd81afc87 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -113,7 +113,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
sizeof(ShmemIndexEnt)));
size = add_size(size, dsm_estimate_size());
size = add_size(size, DSMRegistryShmemSize());
- size = add_size(size, BufferManagerShmemSize());
+ size = add_size(size, BufferManagerShmemSize(shmem_segment));
size = add_size(size, LockManagerShmemSize());
size = add_size(size, PredicateLockShmemSize());
size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 41fdc1e7693..edac9db6a12 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -318,7 +318,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
/* in buf_init.c */
extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
/* in localbuf.c */
extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 79b0b1ef9eb..a7b275b4db9 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
} ShmemSegment;
/* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
@@ -109,7 +109,29 @@ extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
int *memfd_flags);
void PrepareHugePages(void);
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
/* The main segment, contains everything except buffer blocks and related data. */
#define MAIN_SHMEM_SEGMENT 0
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
#endif /* PG_SHMEM_H */
--
2.49.0
From c5717c5b68439abf4488fc3e1c2e47a94c6cd9f3 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 14:16:55 +0200
Subject: [PATCH v5 07/10] Allow to resize shared memory without restart
Add assing hook for shared_buffers to resize shared memory using space,
introduced in the previous commits without requiring PostgreSQL restart.
Essentially the implementation is based on two mechanisms: a
ProcSignalBarrier is used to make sure all processes are starting the
resize procedure simultaneously, and a global Barrier is used to
coordinate after that and make sure all finished processes are waiting
for others that are in progress.
The resize process looks like this:
* The GUC assign hook sets a flag to let the Postmaster know that resize
was requested.
* Postmaster verifies the flag in the event loop, and starts the resize
by emitting a ProcSignal barrier.
* All processes, that participate in ProcSignal mechanism, begin to
process ProcSignal barrier. First a process waits until all processes
have confirmed they received the message and can start simultaneously.
* Every process recalculates shared memory size based on the new
NBuffers, adjusts its size using ftruncate and adjust reservation
permissions with mprotect. One elected process signals the postmaster
to do the same.
* When finished, every process waits on a global ShmemControl barrier,
untill all others are finished as well. This way we ensure three
stages with clear boundaries: before the resize, when all processes
use old NBuffers; during the resize, when processes have mix of old
and new NBuffers, and wait until it's done; after the resize, when all
processes use new NBuffers.
* After all processes are using new value, one of them will initialize
new shared structures (buffer blocks, descriptors, etc) as needed and
broadcast new value of NBuffers via ShmemControl in shared memory.
Other backends are waiting for this operation to finish as well. Then
the barrier is lifted and everything goes as usual.
Since resizing takes time, we need to take into account that during that time:
- New backends can be spawned. They will check status of the barrier
early during the bootstrap, and wait until everything is over to work
with the new NBuffers value.
- Old backends can exit before attempting to resize. Synchronization
used between backends relies on ProcSignalBarrier and waits for all
participants received the message at the beginning to gather all
existing backends.
- Some backends might be blocked and not responsing either before or
after receiving the message. In the first case such backend still
have ProcSignalSlot and should be waited for, in the second case
shared barrier will make sure we still waiting for those backends. In
any case there is an unbounded wait.
- Backends might join barrier in disjoint groups with some time in
between. That means that relying only on the shared dynamic barrier is
not enough -- it will only synchronize resize procedure withing those
groups. That's why we wait first for all participants of ProcSignal
mechanism who received the message.
Here is how it looks like after raising shared_buffers from 128 MB to
512 MB and calling pg_reload_conf():
-- 128 MB
7f87909fc000-7f8798248000 rw-s /memfd:strategy (deleted)
7f8798248000-7f879d6ca000 ---s /memfd:strategy (deleted)
7f879d6ca000-7f87a4e84000 rw-s /memfd:checkpoint (deleted)
7f87a4e84000-7f87aa398000 ---s /memfd:checkpoint (deleted)
7f87aa398000-7f87b1b42000 rw-s /memfd:iocv (deleted)
7f87b1b42000-7f87c3d32000 ---s /memfd:iocv (deleted)
7f87c3d32000-7f87cb59c000 rw-s /memfd:descriptors (deleted)
7f87cb59c000-7f87dd6cc000 ---s /memfd:descriptors (deleted)
7f87dd6cc000-7f87ece38000 rw-s /memfd:buffers (deleted)
^ buffers content, ~247 MB
7f87ece38000-7f8877066000 ---s /memfd:buffers (deleted)
^ reserved space, ~2210 MB
7f8877066000-7f887e7d0000 rw-s /memfd:main (deleted)
7f887e7d0000-7f8890a00000 ---s /memfd:main (deleted)
-- 512 MB
7f87909fc000-7f879866a000 rw-s /memfd:strategy (deleted)
7f879866a000-7f879d6ca000 ---s /memfd:strategy (deleted)
7f879d6ca000-7f87a50f4000 rw-s /memfd:checkpoint (deleted)
7f87a50f4000-7f87aa398000 ---s /memfd:checkpoint (deleted)
7f87aa398000-7f87b1d82000 rw-s /memfd:iocv (deleted)
7f87b1d82000-7f87c3d32000 ---s /memfd:iocv (deleted)
7f87c3d32000-7f87cba1c000 rw-s /memfd:descriptors (deleted)
7f87cba1c000-7f87dd6cc000 ---s /memfd:descriptors (deleted)
7f87dd6cc000-7f8804fb8000 rw-s /memfd:buffers (deleted)
^ buffers content, ~632 MB
7f8804fb8000-7f8877066000 ---s /memfd:buffers (deleted)
^ reserved space, ~1824 MB
7f8877066000-7f887e950000 rw-s /memfd:main (deleted)
7f887e950000-7f8890a00000 ---s /memfd:main (deleted)
The implementation supports only increasing of shared_buffers. For
decreasing the value a similar procedure is needed. But the buffer
blocks with data have to be drained first, so that the actual data set
fits into the new smaller space.
From experiment it turns out that shared mappings have to be extended
separately for each process that uses them. Another rough edge is that a
backend blocked on ReadCommand will not apply shared_buffers change
until it receives something.
Authors: Dmitrii Dolgov, Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 446 ++++++++++++++++++
src/backend/postmaster/checkpointer.c | 12 +-
src/backend/postmaster/postmaster.c | 18 +
src/backend/storage/buffer/buf_init.c | 74 +--
src/backend/storage/ipc/ipci.c | 18 +-
src/backend/storage/ipc/procsignal.c | 46 ++
src/backend/storage/ipc/shmem.c | 23 +-
src/backend/tcop/postgres.c | 10 +
.../utils/activity/wait_event_names.txt | 3 +
src/backend/utils/misc/guc_tables.c | 4 +-
src/include/storage/bufmgr.h | 2 +-
src/include/storage/ipc.h | 3 +
src/include/storage/lwlocklist.h | 1 +
src/include/storage/pg_shmem.h | 26 +
src/include/storage/pmsignal.h | 1 +
src/include/storage/procsignal.h | 1 +
src/tools/pgindent/typedefs.list | 1 +
17 files changed, 644 insertions(+), 45 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index dac011b766b..b3c90d15d52 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -30,13 +30,19 @@
#include "miscadmin.h"
#include "port/pg_bitutils.h"
#include "portability/mem.h"
+#include "storage/bufmgr.h"
#include "storage/dsm.h"
#include "storage/fd.h"
#include "storage/ipc.h"
+#include "storage/lwlock.h"
#include "storage/pg_shmem.h"
+#include "storage/pmsignal.h"
+#include "storage/procsignal.h"
+#include "storage/shmem.h"
#include "utils/guc.h"
#include "utils/guc_hooks.h"
#include "utils/pidfile.h"
+#include "utils/wait_event.h"
/*
@@ -107,6 +113,13 @@ typedef struct AnonymousMapping
static AnonymousMapping Mappings[ANON_MAPPINGS];
+/* Flag telling postmaster that resize is needed */
+volatile bool pending_pm_shmem_resize = false;
+
+/* Keeps track of the previous NBuffers value */
+static int NBuffersOld = -1;
+static int NBuffersPending = -1;
+
/* Keeps track of used mapping segments */
static int next_free_segment = 0;
@@ -161,6 +174,49 @@ static double SHMEM_RESIZE_RATIO[6] = {
*/
static bool huge_pages_on = false;
+/*
+ * Flag telling that we have prepared the memory layout to be resizable. If
+ * false after all shared memory segments creation, it means we failed to setup
+ * needed layout and falled back to the regular non-resizable approach.
+ */
+static bool shmem_resizable = false;
+
+/*
+ * Currently broadcasted value of NBuffers in shared memory.
+ *
+ * Most of the time this value is going to be equal to NBuffers. But if
+ * postmaster is resizing shared memory and a new backend was created
+ * at the same time, there is a possibility for the new backend to inherit the
+ * old NBuffers value, but miss the resize signal if ProcSignal infrastructure
+ * was not initialized yet. Consider this situation:
+ *
+ * Postmaster ------> New Backend
+ * | |
+ * | Launch
+ * | |
+ * | Inherit NBuffers
+ * | |
+ * Resize NBuffers |
+ * | |
+ * Emit Barrier |
+ * | Init ProcSignal
+ * | |
+ * Finish resize |
+ * | |
+ * New NBuffers Old NBuffers
+ *
+ * In this case the backend is not yet ready to receive a signal from
+ * EmitProcSignalBarrier, and will be ignored. The same happens if ProcSignal
+ * is initialized even later, after the resizing was finished.
+ *
+ * To address resulting inconsistency, postmaster broadcasts the current
+ * NBuffers value via shared memory. Every new backend has to verify this value
+ * before it will access the buffer pool: if it differs from its own value,
+ * this indicates a shared memory resize has happened and the backend has to
+ * first synchronize with rest of the pack.
+ */
+ShmemControl *ShmemCtrl = NULL;
+
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
@@ -924,6 +980,349 @@ AnonymousShmemDetach(int status, Datum arg)
}
}
+/*
+ * Resize all shared memory segments based on the current NBuffers value, which
+ * is is applied from NBuffersPending. The actual segment resizing is done via
+ * ftruncate, which will fail if is not sufficient space to expand the anon
+ * file. When finished, based on the new and old values initialize new buffer
+ * blocks if any.
+ *
+ * If reinitializing took place, as the last step this function does buffers
+ * reinitialization as well and broadcasts the new value of NSharedBuffers. All
+ * of that needs to be done only by one backend, the first one that managed to
+ * grab the ShmemResizeLock.
+ */
+bool
+AnonymousShmemResize(void)
+{
+ int numSemas;
+ bool reinit = false;
+ int mmap_flags = PG_MMAP_FLAGS;
+ Size hugepagesize;
+
+ NBuffers = NBuffersPending;
+
+ elog(DEBUG1, "Resize shmem from %d to %d", NBuffersOld, NBuffers);
+
+ /*
+ * XXX: Where to reset the flag is still an open question. E.g. do we
+ * consider a no-op when NBuffers is equal to NBuffersOld a genuine resize
+ * and reset the flag?
+ */
+ pending_pm_shmem_resize = false;
+
+ /*
+ * XXX: Currently only increasing of shared_buffers is supported. For
+ * decreasing something similar has to be done, but buffer blocks with
+ * data have to be drained first.
+ */
+ if(NBuffersOld > NBuffers)
+ return false;
+
+#ifndef MAP_HUGETLB
+ /* PrepareHugePages should have dealt with this case */
+ Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
+#else
+ if (huge_pages_on)
+ {
+ /* Make sure nothing is messed up */
+ Assert(huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY);
+
+ /* Round up the new size to a suitable large value */
+ GetHugePageSize(&hugepagesize, &mmap_flags, NULL);
+ }
+#endif
+
+ for(int i = 0; i < next_free_segment; i++)
+ {
+ /* Note that CalculateShmemSize indirectly depends on NBuffers */
+ Size new_size = CalculateShmemSize(&numSemas, i);
+ AnonymousMapping *m = &Mappings[i];
+
+#ifdef MAP_HUGETLB
+ if (huge_pages_on && (new_size % hugepagesize != 0))
+ new_size += hugepagesize - (new_size % hugepagesize);
+#endif
+
+ if (m->shmem == NULL)
+ continue;
+
+ if (m->shmem_size == new_size)
+ continue;
+
+ if (m->shmem_reserved < new_size)
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+ errmsg("not enough shared memory is reserved"),
+ errhint("You may need to increase \"max_available_memory\".")));
+
+ elog(DEBUG1, "segment[%s]: resize from %zu to %zu at address %p",
+ MappingName(m->shmem_segment), m->shmem_size,
+ new_size, m->shmem);
+
+ /* Resize the backing anon file. */
+ if(ftruncate(m->segment_fd, new_size) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not truncase anonymous file for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ /* Adjust memory accessibility */
+ if(mprotect(m->shmem, new_size, PROT_READ | PROT_WRITE) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not mprotect anonymous shared memory for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ /* If shrinking, make reserved space unavailable again */
+ if(new_size < m->shmem_size &&
+ mprotect(m->shmem + new_size, m->shmem_size - new_size, PROT_NONE) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not mprotect reserved shared memory for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ reinit = true;
+ m->shmem_size = new_size;
+ }
+
+ if (reinit)
+ {
+ if(IsUnderPostmaster &&
+ LWLockConditionalAcquire(ShmemResizeLock, LW_EXCLUSIVE))
+ {
+ /*
+ * If the new NBuffers was already broadcasted, the buffer pool was
+ * already initialized before.
+ *
+ * Since we're not on a hot path, we use lwlocks and do not need to
+ * involve memory barrier.
+ */
+ if(pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) != NBuffers)
+ {
+ /*
+ * Allow the first backend that managed to get the lock to
+ * reinitialize the new portion of buffer pool. Every other
+ * process will wait on the shared barrier for that to finish,
+ * since it's a part of the SHMEM_RESIZE_DONE phase.
+ *
+ * Note that it's enough when only one backend will do that,
+ * even the ShmemInitStruct part. The reason is that resized
+ * shared memory will maintain the same addresses, meaning that
+ * all the pointers are still valid, and we only need to update
+ * structures size in the ShmemIndex once -- any other backend
+ * will pick up this shared structure from the index.
+ *
+ * XXX: This is the right place for buffer eviction as well.
+ */
+ BufferManagerShmemInit(NBuffersOld);
+
+ /* If all fine, broadcast the new value */
+ pg_atomic_write_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
+ }
+
+ LWLockRelease(ShmemResizeLock);
+ }
+ }
+
+ return true;
+}
+
+/*
+ * We are asked to resize shared memory. Wait for all ProcSignal participants
+ * to join the barrier, then do the resize and wait on the barrier until all
+ * participating finish resizing as well -- otherwise we face danger of
+ * inconsistency between backends.
+ *
+ * XXX: If a backend is blocked on ReadCommand in PostgresMain, it will not
+ * proceed with AnonymousShmemResize after receiving SIGHUP, until something
+ * will be sent.
+ */
+bool
+ProcessBarrierShmemResize(Barrier *barrier)
+{
+ Assert(IsUnderPostmaster);
+
+ elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d",
+ NBuffersOld, NBuffersPending, pending_pm_shmem_resize);
+
+ /* Wait until we have seen the new NBuffers value */
+ if (!pending_pm_shmem_resize)
+ return false;
+
+ /*
+ * First thing to do after attaching to the barrier is to wait for others.
+ * We can't simply use BarrierArriveAndWait, because backends might arrive
+ * here in disjoint groups, e.g. first two backends, pause, then second two
+ * backends. If the resize is quick enough that can lead to a situation
+ * when the first group is already finished before the second has appeared,
+ * and the barrier will only synchonize withing those groups.
+ */
+ if (BarrierAttach(barrier) == SHMEM_RESIZE_REQUESTED)
+ WaitForProcSignalBarrierReceived(
+ pg_atomic_read_u64(&ShmemCtrl->Generation));
+
+ /*
+ * Now start the procedure, and elect one backend to ping postmaster to do
+ * the same.
+ *
+ * XXX: If we need to be able to abort resizing, this has to be done later,
+ * after the SHMEM_RESIZE_DONE.
+ */
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+ {
+ Assert(IsUnderPostmaster);
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
+ }
+
+ AnonymousShmemResize();
+
+ /* The second phase means the resize has finished, SHMEM_RESIZE_DONE */
+ BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_DONE);
+
+ BarrierDetach(barrier);
+ return true;
+}
+
+/*
+ * GUC assign hook for shared_buffers. It's recommended for an assign hook to
+ * be as minimal as possible, thus we just request shared memory resize and
+ * remember the previous value.
+ */
+void
+assign_shared_buffers(int newval, void *extra, bool *pending)
+{
+ elog(DEBUG1, "Received SIGHUP for shmem resizing");
+
+ /* Request shared memory resize only when it was initialized */
+ if (next_free_segment != 0)
+ {
+ pending_pm_shmem_resize = true;
+ *pending = true;
+ NBuffersPending = newval;
+ }
+
+ NBuffersOld = NBuffers;
+}
+
+/*
+ * Test if we have somehow missed a shmem resize signal and NBuffers value
+ * differs from NSharedBuffers. If yes, catchup and do resize.
+ */
+void
+AdjustShmemSize(void)
+{
+ uint32 NSharedBuffers = pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers);
+
+ if (NSharedBuffers != NBuffers)
+ {
+ /*
+ * If the broadcasted shared_buffers is different from the one we see,
+ * it could be that the backend has missed a resize signal. To avoid
+ * any inconsistency, adjust the shared mappings, before having a
+ * chance to access the buffer pool.
+ */
+ ereport(LOG,
+ (errmsg("shared_buffers has been changed from %d to %d, "
+ "resize shared memory",
+ NBuffers, NSharedBuffers)));
+ NBuffers = NSharedBuffers;
+ AnonymousShmemResize();
+ }
+}
+
+/*
+ * Start resizing procedure, making sure all existing processes will have
+ * consistent view of shared memory size. Must be called only in postmaster.
+ */
+void
+CoordinateShmemResize(void)
+{
+ elog(DEBUG1, "Coordinating shmem resize from %d to %d",
+ NBuffersOld, NBuffers);
+ Assert(!IsUnderPostmaster);
+
+ /*
+ * We use dynamic barrier to help dealing with backends that were spawned
+ * during the resize.
+ */
+ BarrierInit(&ShmemCtrl->Barrier, 0);
+
+ /*
+ * If the value did not change, or shared memory segments are not
+ * initialized yet, skip the resize.
+ */
+ if (NBuffersPending == NBuffersOld || next_free_segment == 0)
+ {
+ elog(DEBUG1, "Skip resizing, new %d, old %d, free segment %d",
+ NBuffers, NBuffersOld, next_free_segment);
+ return;
+ }
+
+ /*
+ * Shared memory resize requires some coordination done by postmaster,
+ * and consists of three phases:
+ *
+ * - Before the resize all existing backends have the same old NBuffers.
+ * - When resize is in progress, backends are expected to have a
+ * mixture of old a new values. They're not allowed to touch buffer
+ * pool during this time frame.
+ * - After resize has been finished, all existing backends, that can access
+ * the buffer pool, are expected to have the same new value of NBuffers.
+ *
+ * Those phases are ensured by joining the shared barrier associated with
+ * the procedure. Since resizing takes time, we need to take into account
+ * that during that time:
+ *
+ * - New backends can be spawned. They will check status of the barrier
+ * early during the bootstrap, and wait until everything is over to work
+ * with the new NBuffers value.
+ *
+ * - Old backends can exit before attempting to resize. Synchronization
+ * used between backends relies on ProcSignalBarrier and waits for all
+ * participants received the message at the beginning to gather all
+ * existing backends.
+ *
+ * - Some backends might be blocked and not responsing either before or
+ * after receiving the message. In the first case such backend still
+ * have ProcSignalSlot and should be waited for, in the second case
+ * shared barrier will make sure we still waiting for those backends. In
+ * any case there is an unbounded wait.
+ *
+ * - Backends might join barrier in disjoint groups with some time in
+ * between. That means that relying only on the shared dynamic barrier is
+ * not enough -- it will only synchronize resize procedure withing those
+ * groups. That's why we wait first for all participants of ProcSignal
+ * mechanism who received the message.
+ */
+ elog(DEBUG1, "Emit a barrier for shmem resizing");
+ pg_atomic_init_u64(&ShmemCtrl->Generation,
+ EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SHMEM_RESIZE));
+
+ /* To order everything after setting Generation value */
+ pg_memory_barrier();
+
+ /*
+ * After that postmaster waits for PMSIGNAL_SHMEM_RESIZE as a sign that all
+ * the rest of the pack has started the procedure and it can resize shared
+ * memory as well.
+ *
+ * Normally we would call WaitForProcSignalBarrier here to wait until every
+ * backend has reported on the ProcSignalBarrier. But for shared memory
+ * resize we don't need this, as every participating backend will
+ * synchronize on the ProcSignal barrier. In fact even if we would like to
+ * wait here, it wouldn't be possible -- we're in the postmaster, without
+ * any waiting infrastructure available.
+ *
+ * If at some point it will turn out that waiting is essential, we would
+ * need to consider some alternatives. E.g. it could be a designated
+ * coordination process, which is not a postmaster. Another option would be
+ * to introduce a CoordinateShmemResize lock and allow only one process to
+ * take it (this probably would have to be something different than
+ * LWLocks, since they block interrupts, and coordination relies on them).
+ */
+}
+
/*
* PGSharedMemoryCreate
*
@@ -1239,3 +1638,50 @@ PGSharedMemoryDetach(void)
}
}
}
+
+void
+WaitOnShmemBarrier()
+{
+ Barrier *barrier = &ShmemCtrl->Barrier;
+
+ /* Nothing to do if resizing is not started */
+ if (BarrierPhase(barrier) < SHMEM_RESIZE_START)
+ return;
+
+ BarrierAttach(barrier);
+
+ /* Otherwise wait through all available phases */
+ while (BarrierPhase(barrier) < SHMEM_RESIZE_DONE)
+ {
+ ereport(LOG, (errmsg("ProcSignal barrier is in phase %d, waiting",
+ BarrierPhase(barrier))));
+
+ BarrierArriveAndWait(barrier, 0);
+ }
+
+ BarrierDetach(barrier);
+}
+
+void
+ShmemControlInit(void)
+{
+ bool foundShmemCtrl;
+
+ ShmemCtrl = (ShmemControl *)
+ ShmemInitStruct("Shmem Control", sizeof(ShmemControl),
+ &foundShmemCtrl);
+
+ if (!foundShmemCtrl)
+ {
+ /*
+ * The barrier is missing here, it will be initialized right before
+ * starting the resizing process as a convenient way to reset it.
+ */
+
+ /* Initialize with the currently known value */
+ pg_atomic_init_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
+
+ /* shmem_resizable should be initialized by now */
+ ShmemCtrl->Resizable = shmem_resizable;
+ }
+}
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index fda91ffd1ce..ab08e1a182b 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -638,9 +638,12 @@ CheckpointerMain(const void *startup_data, size_t startup_data_len)
static void
ProcessCheckpointerInterrupts(void)
{
- if (ProcSignalBarrierPending)
- ProcessProcSignalBarrier();
-
+ /*
+ * Reloading config can trigger further signals, complicating interrupts
+ * processing -- so let it run first.
+ *
+ * XXX: Is there any need in memory barrier after ProcessConfigFile?
+ */
if (ConfigReloadPending)
{
ConfigReloadPending = false;
@@ -660,6 +663,9 @@ ProcessCheckpointerInterrupts(void)
UpdateSharedMemoryConfig();
}
+ if (ProcSignalBarrierPending)
+ ProcessProcSignalBarrier();
+
/* Perform logging of memory contexts of this process */
if (LogMemoryContextPending)
ProcessLogMemoryContextInterrupt();
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 490f7ce3664..f0cb0098dcd 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -426,6 +426,7 @@ static void process_pm_pmsignal(void);
static void process_pm_child_exit(void);
static void process_pm_reload_request(void);
static void process_pm_shutdown_request(void);
+static void process_pm_shmem_resize(void);
static void dummy_handler(SIGNAL_ARGS);
static void CleanupBackend(PMChild *bp, int exitstatus);
static void HandleChildCrash(int pid, int exitstatus, const char *procname);
@@ -1694,6 +1695,9 @@ ServerLoop(void)
if (pending_pm_pmsignal)
process_pm_pmsignal();
+ if (pending_pm_shmem_resize)
+ process_pm_shmem_resize();
+
if (events[i].events & WL_SOCKET_ACCEPT)
{
ClientSocket s;
@@ -2039,6 +2043,17 @@ process_pm_reload_request(void)
}
}
+static void
+process_pm_shmem_resize(void)
+{
+ /*
+ * Failure to resize is considered to be fatal and will not be
+ * retried, which means we can disable pending flag right here.
+ */
+ pending_pm_shmem_resize = false;
+ CoordinateShmemResize();
+}
+
/*
* pg_ctl uses SIGTERM, SIGINT and SIGQUIT to request different types of
* shutdown.
@@ -3852,6 +3867,9 @@ process_pm_pmsignal(void)
request_state_update = true;
}
+ if (CheckPostmasterSignal(PMSIGNAL_SHMEM_RESIZE))
+ AnonymousShmemResize();
+
/*
* Try to advance postmaster's state machine, if a child requests it.
*/
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index bd68b69ee98..8c1ea623392 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -17,6 +17,7 @@
#include "storage/aio.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
+#include "storage/pg_shmem.h"
BufferDescPadded *BufferDescriptors;
char *BufferBlocks;
@@ -62,18 +63,28 @@ CkptSortItem *CkptBufferIds;
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend). Size of data structures initialized
- * here depends on NBuffers, and to be able to change NBuffers without a
- * restart we store each structure into a separate shared memory segment, which
- * could be resized on demand.
+ * postmaster, or in a standalone backend) or during shared-memory resize. Size
+ * of data structures initialized here depends on NBuffers, and to be able to
+ * change NBuffers without a restart we store each structure into a separate
+ * shared memory segment, which could be resized on demand.
+ *
+ * FirstBufferToInit tells where to start initializing buffers. For
+ * initialization it always will be zero, but when resizing shared-memory it
+ * indicates the number of already initialized buffers.
+ *
+ * No locks are taking in this function, it is the caller responsibility to
+ * make sure only one backend can work with new buffers.
*/
void
-BufferManagerShmemInit(void)
+BufferManagerShmemInit(int FirstBufferToInit)
{
bool foundBufs,
foundDescs,
foundIOCV,
foundBufCkpt;
+ int i;
+ elog(DEBUG1, "BufferManagerShmemInit from %d to %d",
+ FirstBufferToInit, NBuffers);
/* Align descriptors to a cacheline boundary. */
BufferDescriptors = (BufferDescPadded *)
@@ -110,43 +121,44 @@ BufferManagerShmemInit(void)
{
/* should find all of these, or none of them */
Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
- /* note: this path is only taken in EXEC_BACKEND case */
- }
- else
- {
- int i;
-
/*
- * Initialize all the buffer headers.
+ * note: this path is only taken in EXEC_BACKEND case when initializing
+ * shared memory, or in all cases when resizing shared memory.
*/
- for (i = 0; i < NBuffers; i++)
- {
- BufferDesc *buf = GetBufferDescriptor(i);
+ }
- ClearBufferTag(&buf->tag);
+#ifndef EXEC_BACKEND
+ /*
+ * Initialize all the buffer headers.
+ */
+ for (i = FirstBufferToInit; i < NBuffers; i++)
+ {
+ BufferDesc *buf = GetBufferDescriptor(i);
- pg_atomic_init_u32(&buf->state, 0);
- buf->wait_backend_pgprocno = INVALID_PROC_NUMBER;
+ ClearBufferTag(&buf->tag);
- buf->buf_id = i;
+ pg_atomic_init_u32(&buf->state, 0);
+ buf->wait_backend_pgprocno = INVALID_PROC_NUMBER;
- pgaio_wref_clear(&buf->io_wref);
+ buf->buf_id = i;
- /*
- * Initially link all the buffers together as unused. Subsequent
- * management of this list is done by freelist.c.
- */
- buf->freeNext = i + 1;
+ pgaio_wref_clear(&buf->io_wref);
- LWLockInitialize(BufferDescriptorGetContentLock(buf),
- LWTRANCHE_BUFFER_CONTENT);
+ /*
+ * Initially link all the buffers together as unused. Subsequent
+ * management of this list is done by freelist.c.
+ */
+ buf->freeNext = i + 1;
- ConditionVariableInit(BufferDescriptorGetIOCV(buf));
- }
+ LWLockInitialize(BufferDescriptorGetContentLock(buf),
+ LWTRANCHE_BUFFER_CONTENT);
- /* Correct last entry of linked list */
- GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
+ ConditionVariableInit(BufferDescriptorGetIOCV(buf));
}
+#endif
+
+ /* Correct last entry of linked list */
+ GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2dbd81afc87..c5725f55120 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -84,6 +84,9 @@ RequestAddinShmemSpace(Size size)
*
* If num_semaphores is not NULL, it will be set to the number of semaphores
* required.
+ *
+ * XXX: Calculation for non main shared memory segments are incorrect, it
+ * includes more than needed for buffers only.
*/
Size
CalculateShmemSize(int *num_semaphores, int shmem_segment)
@@ -151,6 +154,14 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
size = add_size(size, SlotSyncShmemSize());
size = add_size(size, AioShmemSize());
+ /*
+ * XXX: For some reason slightly more memory is needed for larger
+ * shared_buffers, but this size is enough for any large value I've tested
+ * with. Is it a mistake in how slots are split, or there was a hidden
+ * inconsistency in shmem calculation?
+ */
+ size = add_size(size, 1024 * 1024 * 100);
+
/* include additional requested shmem from preload libraries */
size = add_size(size, total_addin_request);
@@ -298,7 +309,7 @@ CreateOrAttachShmemStructs(void)
CommitTsShmemInit();
SUBTRANSShmemInit();
MultiXactShmemInit();
- BufferManagerShmemInit();
+ BufferManagerShmemInit(0);
/*
* Set up lock manager
@@ -310,6 +321,11 @@ CreateOrAttachShmemStructs(void)
*/
PredicateLockShmemInit();
+ /*
+ * Set up shared memory resize manager
+ */
+ ShmemControlInit();
+
/*
* Set up process table
*/
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index c6bec9be423..d7b56a18b24 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -27,6 +27,7 @@
#include "storage/condition_variable.h"
#include "storage/ipc.h"
#include "storage/latch.h"
+#include "storage/pg_shmem.h"
#include "storage/shmem.h"
#include "storage/sinval.h"
#include "storage/smgr.h"
@@ -113,6 +114,10 @@ static bool CheckProcSignal(ProcSignalReason reason);
static void CleanupProcSignalState(int status, Datum arg);
static void ResetProcSignalBarrierBits(uint32 flags);
+#ifdef DEBUG_SHMEM_RESIZE
+bool delay_proc_signal_init = false;
+#endif
+
/*
* ProcSignalShmemSize
* Compute space needed for ProcSignal's shared memory
@@ -176,6 +181,43 @@ ProcSignalInit(const uint8 *cancel_key, int cancel_key_len)
uint32 old_pss_pid;
Assert(cancel_key_len >= 0 && cancel_key_len <= MAX_CANCEL_KEY_LENGTH);
+
+#ifdef DEBUG_SHMEM_RESIZE
+ /*
+ * Introduced for debugging purposes. You can change the variable at
+ * runtime using gdb, then start new backends with delayed ProcSignal
+ * initialization. Simple pg_usleep wont work here due to SIGHUP interrupt
+ * needed for testing. Taken from pg_sleep;
+ */
+ if (delay_proc_signal_init)
+ {
+#define GetNowFloat() ((float8) GetCurrentTimestamp() / 1000000.0)
+ float8 endtime = GetNowFloat() + 5;
+
+ for (;;)
+ {
+ float8 delay;
+ long delay_ms;
+
+ CHECK_FOR_INTERRUPTS();
+
+ delay = endtime - GetNowFloat();
+ if (delay >= 600.0)
+ delay_ms = 600000;
+ else if (delay > 0.0)
+ delay_ms = (long) (delay * 1000.0);
+ else
+ break;
+
+ (void) WaitLatch(MyLatch,
+ WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+ delay_ms,
+ WAIT_EVENT_PG_SLEEP);
+ ResetLatch(MyLatch);
+ }
+ }
+#endif
+
if (MyProcNumber < 0)
elog(ERROR, "MyProcNumber not set");
if (MyProcNumber >= NumProcSignalSlots)
@@ -615,6 +657,10 @@ ProcessProcSignalBarrier(void)
case PROCSIGNAL_BARRIER_SMGRRELEASE:
processed = ProcessBarrierSmgrRelease();
break;
+ case PROCSIGNAL_BARRIER_SHMEM_RESIZE:
+ processed = ProcessBarrierShmemResize(
+ &ShmemCtrl->Barrier);
+ break;
}
/*
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 8d025f0e907..9fa277b91d7 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -498,17 +498,26 @@ ShmemInitStructInSegment(const char *name, Size size, bool *foundPtr,
{
/*
* Structure is in the shmem index so someone else has allocated it
- * already. The size better be the same as the size we are trying to
- * initialize to, or there is a name conflict (or worse).
+ * already. Verify the structure's size:
+ * - If it's the same, we've found the expected structure.
+ * - If it's different, we're resizing the expected structure.
+ *
+ * XXX: There is an implicit assumption this can only happen in
+ * "resizable" segments, where only one shared structure is allowed.
+ * This has to be implemented more cleanly.
*/
if (result->size != size)
{
- LWLockRelease(ShmemIndexLock);
- ereport(ERROR,
- (errmsg("ShmemIndex entry size is wrong for data structure"
- " \"%s\": expected %zu, actual %zu",
- name, size, result->size)));
+ Size delta = size - result->size;
+
+ result->size = size;
+
+ /* Reflect size change in the shared segment */
+ SpinLockAcquire(Segments[shmem_segment].ShmemLock);
+ Segments[shmem_segment].ShmemSegHdr->freeoffset += delta;
+ SpinLockRelease(Segments[shmem_segment].ShmemLock);
}
+
structPtr = result->location;
}
else
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 0d1b6466d1e..0942d2bffe2 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -62,6 +62,7 @@
#include "rewrite/rewriteHandler.h"
#include "storage/bufmgr.h"
#include "storage/ipc.h"
+#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
@@ -4309,6 +4310,15 @@ PostgresMain(const char *dbname, const char *username)
*/
BeginReportingGUCOptions();
+ /* Verify the shared barrier, if it's still active: join and wait. */
+ WaitOnShmemBarrier();
+
+ /*
+ * After waiting on the barrier above we guaranteed to have NSharedBuffers
+ * broadcasted, so we can use it in the function below.
+ */
+ AdjustShmemSize();
+
/*
* Also set up handler to log session end; we have to wait till now to be
* sure Log_disconnections has its final value.
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 4da68312b5f..691fa14e9e3 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -155,6 +155,8 @@ REPLICATION_ORIGIN_DROP "Waiting for a replication origin to become inactive so
REPLICATION_SLOT_DROP "Waiting for a replication slot to become inactive so it can be dropped."
RESTORE_COMMAND "Waiting for <xref linkend="guc-restore-command"/> to complete."
SAFE_SNAPSHOT "Waiting to obtain a valid snapshot for a <literal>READ ONLY DEFERRABLE</literal> transaction."
+SHMEM_RESIZE_START "Waiting for other backends to start resizing shared memory."
+SHMEM_RESIZE_DONE "Waiting for other backends to finish resizing shared memory."
SYNC_REP "Waiting for confirmation from a remote server during synchronous replication."
WAL_BUFFER_INIT "Waiting on WAL buffer to be initialized."
WAL_RECEIVER_EXIT "Waiting for the WAL receiver to exit."
@@ -352,6 +354,7 @@ DSMRegistry "Waiting to read or update the dynamic shared memory registry."
InjectionPoint "Waiting to read or update information related to injection points."
SerialControl "Waiting to read or update shared <filename>pg_serial</filename> state."
AioWorkerSubmissionQueue "Waiting to access AIO worker submission queue."
+ShmemResize "Waiting to resize shared memory."
#
# END OF PREDEFINED LWLOCKS (DO NOT CHANGE THIS LINE)
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index a221e446d6a..d8acec0f911 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2366,14 +2366,14 @@ struct config_int ConfigureNamesInt[] =
* checking for overflow, so we mustn't allow more than INT_MAX / 2.
*/
{
- {"shared_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+ {"shared_buffers", PGC_SIGHUP, RESOURCES_MEM,
gettext_noop("Sets the number of shared memory buffers used by the server."),
NULL,
GUC_UNIT_BLOCKS
},
&NBuffers,
16384, 16, INT_MAX / 2,
- NULL, NULL, NULL
+ NULL, assign_shared_buffers, NULL
},
{
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index edac9db6a12..4239ebe640b 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -317,7 +317,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
int32 *buffers_skipped);
/* in buf_init.c */
-extern void BufferManagerShmemInit(void);
+extern void BufferManagerShmemInit(int);
extern Size BufferManagerShmemSize(int);
/* in localbuf.c */
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 6ebda479ced..bb7ae4d33b3 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -64,6 +64,7 @@ typedef void (*shmem_startup_hook_type) (void);
/* ipc.c */
extern PGDLLIMPORT bool proc_exit_inprogress;
extern PGDLLIMPORT bool shmem_exit_inprogress;
+extern PGDLLIMPORT volatile bool pending_pm_shmem_resize;
pg_noreturn extern void proc_exit(int code);
extern void shmem_exit(int code);
@@ -83,5 +84,7 @@ extern void CreateSharedMemoryAndSemaphores(void);
extern void AttachSharedMemoryStructs(void);
#endif
extern void InitializeShmemGUCs(void);
+extern void CoordinateShmemResize(void);
+extern bool AnonymousShmemResize(void);
#endif /* IPC_H */
diff --git a/src/include/storage/lwlocklist.h b/src/include/storage/lwlocklist.h
index a9681738146..558da6fdd55 100644
--- a/src/include/storage/lwlocklist.h
+++ b/src/include/storage/lwlocklist.h
@@ -84,3 +84,4 @@ PG_LWLOCK(50, DSMRegistry)
PG_LWLOCK(51, InjectionPoint)
PG_LWLOCK(52, SerialControl)
PG_LWLOCK(53, AioWorkerSubmissionQueue)
+PG_LWLOCK(54, ShmemResize)
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index a7b275b4db9..bccdd45b1f7 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -24,6 +24,7 @@
#ifndef PG_SHMEM_H
#define PG_SHMEM_H
+#include "storage/barrier.h"
#include "storage/dsm_impl.h"
#include "storage/spin.h"
@@ -56,6 +57,25 @@ typedef struct ShmemSegment
extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
+/*
+ * ShmemControl is shared between backends and helps to coordinate shared
+ * memory resize.
+ */
+typedef struct
+{
+ pg_atomic_uint32 NSharedBuffers;
+ Barrier Barrier;
+ pg_atomic_uint64 Generation;
+ bool Resizable;
+} ShmemControl;
+
+extern PGDLLIMPORT ShmemControl *ShmemCtrl;
+
+/* The phases for shared memory resizing, used by for ProcSignal barrier. */
+#define SHMEM_RESIZE_REQUESTED 0
+#define SHMEM_RESIZE_START 1
+#define SHMEM_RESIZE_DONE 2
+
/* GUC variables */
extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
@@ -109,6 +129,12 @@ extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
int *memfd_flags);
void PrepareHugePages(void);
+bool ProcessBarrierShmemResize(Barrier *barrier);
+void assign_shared_buffers(int newval, void *extra, bool *pending);
+void AdjustShmemSize(void);
+extern void WaitOnShmemBarrier(void);
+extern void ShmemControlInit(void);
+
/*
* To be able to dynamically resize largest parts of the data stored in shared
* memory, we split it into multiple shared memory mappings segments. Each
diff --git a/src/include/storage/pmsignal.h b/src/include/storage/pmsignal.h
index 428aa3fd68a..1a55bf57a70 100644
--- a/src/include/storage/pmsignal.h
+++ b/src/include/storage/pmsignal.h
@@ -42,6 +42,7 @@ typedef enum
PMSIGNAL_START_WALRECEIVER, /* start a walreceiver */
PMSIGNAL_ADVANCE_STATE_MACHINE, /* advance postmaster's state machine */
PMSIGNAL_XLOG_IS_SHUTDOWN, /* ShutdownXLOG() completed */
+ PMSIGNAL_SHMEM_RESIZE, /* resize shared memory */
} PMSignalReason;
#define NUM_PMSIGNALS (PMSIGNAL_XLOG_IS_SHUTDOWN+1)
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 2733bbb8c5b..97033f84dce 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -54,6 +54,7 @@ typedef enum
typedef enum
{
PROCSIGNAL_BARRIER_SMGRRELEASE, /* ask smgr to close files */
+ PROCSIGNAL_BARRIER_SHMEM_RESIZE, /* ask backends to resize shared memory */
} ProcSignalBarrierType;
/*
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 32d6e718adc..36e25ea8cd6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2751,6 +2751,7 @@ ShellTypeInfo
ShippableCacheEntry
ShippableCacheKey
ShmemIndexEnt
+ShmemControl
ShutdownForeignScan_function
ShutdownInformation
ShutdownMode
--
2.49.0
From 5e190dc84ce7078b6c680d18736e56be90cecdab Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Thu, 19 Jun 2025 17:38:29 +0200
Subject: [PATCH v5 08/10] Support shrinking shared buffers
When shrinking the shared buffers pool, each buffer in the area being
shrunk needs to be flushed if it's dirty so as not to loose the changes
to that buffer after shrinking. Also, each such buffer needs to be
removed from the buffer mapping table so that backends do not access it
after shrinking.
Buffer eviction requires a separate barrier phase for two reasons:
1. No other backend should map a new page to any of buffers being
evicted when eviction is in progress. So they wait while eviction is
in progress.
2. Since a pinned buffer has the pin recorded in the backend local
memory as well as the buffer descriptor (which is in shared memory),
eviction should not coincide with remapping the shared memory of a
backend. Otherwise we might loose consistency of local and shared
pinning records. Hence it needs to be carried out in
ProcessBarrierShmemResize() and not in AnonymousShmemResize() as
indicated by now removed comment.
If a buffer being evicted is pinned, we raise a FATAL error but this should
improve. There are multiple options 1. to wait for the pinned buffer to get
unpinned, 2. the backend is killed or it itself cancels the query or 3.
rollback the operation. Note that option 1 and 2 would require the pinning
related local and shared records to be accessed. But we need infrastructure to
do either of this right now.
Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 42 +++++---
src/backend/storage/buffer/buf_init.c | 8 +-
src/backend/storage/buffer/bufmgr.c | 95 +++++++++++++++++++
src/backend/storage/buffer/freelist.c | 68 +++++++++++++
.../utils/activity/wait_event_names.txt | 1 +
src/include/storage/buf_internals.h | 1 +
src/include/storage/bufmgr.h | 1 +
src/include/storage/pg_shmem.h | 1 +
8 files changed, 202 insertions(+), 15 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index b3c90d15d52..e612a83c9f0 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -1011,14 +1011,6 @@ AnonymousShmemResize(void)
*/
pending_pm_shmem_resize = false;
- /*
- * XXX: Currently only increasing of shared_buffers is supported. For
- * decreasing something similar has to be done, but buffer blocks with
- * data have to be drained first.
- */
- if(NBuffersOld > NBuffers)
- return false;
-
#ifndef MAP_HUGETLB
/* PrepareHugePages should have dealt with this case */
Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
@@ -1112,11 +1104,14 @@ AnonymousShmemResize(void)
* all the pointers are still valid, and we only need to update
* structures size in the ShmemIndex once -- any other backend
* will pick up this shared structure from the index.
- *
- * XXX: This is the right place for buffer eviction as well.
*/
BufferManagerShmemInit(NBuffersOld);
+ /*
+ * Wipe out the evictor PID so that it can be used for the next
+ * buffer resizing operation.
+ */
+ ShmemCtrl->evictor_pid = 0;
/* If all fine, broadcast the new value */
pg_atomic_write_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
}
@@ -1169,11 +1164,31 @@ ProcessBarrierShmemResize(Barrier *barrier)
* XXX: If we need to be able to abort resizing, this has to be done later,
* after the SHMEM_RESIZE_DONE.
*/
- if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+
+ /*
+ * Evict extra buffers when shrinking shared buffers. We need to do this
+ * while the memory for extra buffers is still mapped i.e. before remapping
+ * the shared memory segments to a smaller memory area.
+ */
+ if (NBuffersOld > NBuffersPending)
{
- Assert(IsUnderPostmaster);
- SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
+ BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START);
+
+ /*
+ * TODO: If the buffer eviction fails for any reason, we should
+ * gracefully rollback the shared buffer resizing and try again. But the
+ * infrastructure to do so is not available right now. Hence just raise
+ * a FATAL so that the system restarts.
+ */
+ if (!EvictExtraBuffers(NBuffersPending, NBuffersOld))
+ elog(FATAL, "buffer eviction failed");
+
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_EVICT))
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
}
+ else
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
AnonymousShmemResize();
@@ -1683,5 +1698,6 @@ ShmemControlInit(void)
/* shmem_resizable should be initialized by now */
ShmemCtrl->Resizable = shmem_resizable;
+ ShmemCtrl->evictor_pid = 0;
}
}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 8c1ea623392..6f5743036a2 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -157,8 +157,12 @@ BufferManagerShmemInit(int FirstBufferToInit)
}
#endif
- /* Correct last entry of linked list */
- GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
+ /*
+ * Correct last entry of linked list, when initializing the buffers or when
+ * expanding the buffers.
+ */
+ if (FirstBufferToInit < NBuffers)
+ GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 667aa0c0c78..169a44dd9fc 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -57,6 +57,7 @@
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/read_stream.h"
#include "storage/smgr.h"
@@ -7453,3 +7454,97 @@ const PgAioHandleCallbacks aio_local_buffer_readv_cb = {
.complete_local = local_buffer_readv_complete,
.report = buffer_readv_report,
};
+
+/*
+ * When shrinking shared buffers pool, evict the buffers which will not be part
+ * of the shrunk buffer pool.
+ */
+bool
+EvictExtraBuffers(int newBufSize, int oldBufSize)
+{
+ bool result = true;
+
+ /*
+ * If the buffer being evicated is locked, this function will need to wait.
+ * This function should not be called from a Postmaster since it can not wait on a lock.
+ */
+ Assert(IsUnderPostmaster);
+
+ /*
+ * Let only one backend perform eviction. We could split the work across all
+ * the backends but that doesn't seem necessary.
+ *
+ * The first backend to acquire ShmemResizeLock, sets its own PID as the
+ * evictor PID for other backends to know that the eviction is in progress or
+ * has already been performed. The evictor backend releases the lock when it
+ * finishes eviction. While the eviction is in progress, backends other than
+ * evictor backend won't be able to take the lock. They won't perform
+ * eviction. A backend may acquire the lock after eviction has completed, but
+ * it will not perform eviction since the evictor PID is already set. Evictor
+ * PID is reset only when the buffer resizing finishes. Thus only one backend
+ * will perform eviction in a given instance of shared buffers resizing.
+ *
+ * Any backend which acquires this lock will release it before the eviction
+ * phase finishes, hence the same lock can be reused for the next phase of
+ * resizing buffers.
+ */
+ if (LWLockConditionalAcquire(ShmemResizeLock, LW_EXCLUSIVE))
+ {
+ if (ShmemCtrl->evictor_pid == 0)
+ {
+ ShmemCtrl->evictor_pid = MyProcPid;
+
+ StrategyPurgeFreeList(newBufSize);
+
+ /*
+ * TODO: Before evicting any buffer, we should check whether any of the
+ * buffers are pinned. If we find that a buffer is pinned after evicting
+ * most of them, that will impact performance since all those evicted
+ * buffers might need to be read again.
+ */
+ for (Buffer buf = newBufSize + 1; buf <= oldBufSize; buf++)
+ {
+ BufferDesc *desc = GetBufferDescriptor(buf - 1);
+ uint32 buf_state;
+ bool buffer_flushed;
+
+ buf_state = pg_atomic_read_u32(&desc->state);
+
+ /*
+ * Nobody is expected to touch the buffers while resizing is
+ * going one hence unlocked precheck should be safe and saves
+ * some cycles.
+ */
+ if (!(buf_state & BM_VALID))
+ continue;
+
+ /*
+ * XXX: Looks like CurrentResourceOwner can be NULL here, find
+ * another one in that case?
+ * */
+ if (CurrentResourceOwner)
+ ResourceOwnerEnlarge(CurrentResourceOwner);
+
+ ReservePrivateRefCountEntry();
+
+ LockBufHdr(desc);
+
+ /*
+ * Now that we have locked buffer descriptor, make sure that the
+ * buffer without valid data has been skipped above.
+ */
+ Assert(buf_state & BM_VALID);
+
+ if (!EvictUnpinnedBufferInternal(desc, &buffer_flushed))
+ {
+ elog(WARNING, "could not remove buffer %u, it is pinned", buf);
+ result = false;
+ break;
+ }
+ }
+ }
+ LWLockRelease(ShmemResizeLock);
+ }
+
+ return result;
+}
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index bd390f2709d..7b9ed010e2f 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -527,6 +527,74 @@ StrategyInitialize(bool init)
}
+/*
+ * StrategyPurgeFreeList -- remove all buffers with id higher than the number of
+ * buffers in the buffer pool.
+ *
+ * This is called before evicting buffers while shrinking shared buffers, so that
+ * the free list does not reference a buffer that will be removed.
+ *
+ * The function is called after resizing has started and thus nobody should be
+ * traversing the free list and also not touching the buffers.
+ */
+void
+StrategyPurgeFreeList(int numBuffers)
+{
+ int firstBuffer = FREENEXT_END_OF_LIST;
+ int nextFree = StrategyControl->firstFreeBuffer;
+ BufferDesc *prevValidBuf = NULL;
+
+ SpinLockAcquire(&StrategyControl->buffer_strategy_lock);
+
+ while (nextFree != FREENEXT_END_OF_LIST)
+ {
+ BufferDesc *buf = GetBufferDescriptor(nextFree);
+
+ /* nextFree should be id of buffer being examined. */
+ Assert(nextFree == buf->buf_id);
+ /* The buffer should not be marked as not in the list. */
+ Assert(buf->freeNext != FREENEXT_NOT_IN_LIST);
+
+ /*
+ * If the buffer is within the new size of pool, keep it in the free list
+ * otherwise discard it.
+ */
+ if (buf->buf_id < numBuffers)
+ {
+ if (prevValidBuf != NULL)
+ prevValidBuf->freeNext = buf->buf_id;
+ prevValidBuf = buf;
+
+ /* Save the first free buffer in the list if not already known. */
+ if (firstBuffer == FREENEXT_NOT_IN_LIST)
+ firstBuffer = nextFree;
+ }
+ /* Examine the next buffer in the free list. */
+ nextFree = buf->freeNext;
+ }
+
+ /* Update the last valid free buffer, if there's any. */
+ if (prevValidBuf != NULL)
+ {
+ StrategyControl->lastFreeBuffer = prevValidBuf->buf_id;
+ prevValidBuf->freeNext = FREENEXT_END_OF_LIST;
+ }
+ else
+ StrategyControl->lastFreeBuffer = FREENEXT_END_OF_LIST;
+
+ /* Update first valid free buffer, if there's any. */
+ StrategyControl->firstFreeBuffer = firstBuffer;
+
+ SpinLockRelease(&StrategyControl->buffer_strategy_lock);
+
+ /*
+ * TODO: following was suggested by AI. Check whether it is required.
+ * If we removed all buffers from the freelist, reset the clock sweep
+ * pointer to zero. This is not strictly necessary, but it seems like a
+ * good idea to avoid confusion.
+ */
+}
+
/* ----------------------------------------------------------------
* Backend-private buffer ring management
* ----------------------------------------------------------------
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 691fa14e9e3..0c588b69a90 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -156,6 +156,7 @@ REPLICATION_SLOT_DROP "Waiting for a replication slot to become inactive so it c
RESTORE_COMMAND "Waiting for <xref linkend="guc-restore-command"/> to complete."
SAFE_SNAPSHOT "Waiting to obtain a valid snapshot for a <literal>READ ONLY DEFERRABLE</literal> transaction."
SHMEM_RESIZE_START "Waiting for other backends to start resizing shared memory."
+SHMEM_RESIZE_EVICT "Waiting for other backends to finish buffer evication phase."
SHMEM_RESIZE_DONE "Waiting for other backends to finish resizing shared memory."
SYNC_REP "Waiting for confirmation from a remote server during synchronous replication."
WAL_BUFFER_INIT "Waiting on WAL buffer to be initialized."
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 0dec7d93b3b..add15e3723b 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -453,6 +453,7 @@ extern void StrategyNotifyBgWriter(int bgwprocno);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);
+extern void StrategyPurgeFreeList(int numBuffers);
extern bool have_free_buffer(void);
/* buf_table.c */
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 4239ebe640b..0c554f0b130 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -315,6 +315,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
int32 *buffers_evicted,
int32 *buffers_flushed,
int32 *buffers_skipped);
+extern bool EvictExtraBuffers(int fromBuf, int toBuf);
/* in buf_init.c */
extern void BufferManagerShmemInit(int);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index bccdd45b1f7..9a3e68f76d8 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -64,6 +64,7 @@ extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
typedef struct
{
pg_atomic_uint32 NSharedBuffers;
+ pid_t evictor_pid;
Barrier Barrier;
pg_atomic_uint64 Generation;
bool Resizable;
--
2.49.0
From 475fffc314b4d5975faf94d43504f2dcc0f1dc8d Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Thu, 19 Jun 2025 17:38:51 +0200
Subject: [PATCH v5 09/10] Reinitialize StrategyControl after resizing buffers
... and BgBufferSync and ClockSweepTick adjustments
The commit introduces a separate function StrategyReInitialize() instead
of reusing StrategyInitialize() since some of the things that the second
one does are not required in the first one. Here's list of what
StrategyReInitialize() does and how does it differ from
StrategyInitialize().
1. When expanding the buffer pool add new buffers to the free list.
2. When shrinking buffers, we remove any buffers, in the area being
shrunk, from the freelist. While doing so we adjust the first and
last free buffer pointers in the StrategyControl area. Hence nothing
more needed after resizing.
3. Check the sanity of the free buffer list is added after resizing.
4. StrategyControl pointer needn't be fetched again since it should not
change. But added an Assert to make sure the pointer is valid.
5. &StrategyControl->buffer_strategy_lock need not be initialized again.
6. nextVictimBuffer, completePasses and numBufferAllocs are viewed in
the context of NBuffers. Now that NBuffers itself has changed, those
three do not make sense. Reset them as if the server has restarted
again.
This commit introduces a flag delay_shmem_resize, which postgresql
backends and workers can use to signal the coordinator to delay resizing
operation. Background writer sets this flag when its scanning buffers. Background
writer is blocked when the actual resizing is in progress. But if
resizing is about to begin, it does not scan the buffers by returning
from BgBufferSync(). It stops a scan in progress when it sees that the
resizing has begun. After the resizing is finished, it adjusts the
collected statistics according to the new size of the buffer pool at the
end of barrier processing.
Once the buffer resizing is finished, before resuming the regular
operation, bgwriter resets the information saved so far. This
information is viewed in the context of NBuffers and hence does not make
sense after NBuffer has changed.
Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 24 ++++-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/storage/buffer/buf_init.c | 11 ++-
src/backend/storage/buffer/bufmgr.c | 74 ++++++++++----
src/backend/storage/buffer/freelist.c | 133 ++++++++++++++++++++++++++
src/include/storage/buf_internals.h | 1 +
src/include/storage/bufmgr.h | 3 +-
src/include/storage/ipc.h | 1 +
8 files changed, 226 insertions(+), 23 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index e612a83c9f0..e61a557966b 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -115,6 +115,7 @@ static AnonymousMapping Mappings[ANON_MAPPINGS];
/* Flag telling postmaster that resize is needed */
volatile bool pending_pm_shmem_resize = false;
+volatile bool delay_shmem_resize = false;
/* Keeps track of the previous NBuffers value */
static int NBuffersOld = -1;
@@ -1118,6 +1119,12 @@ AnonymousShmemResize(void)
LWLockRelease(ShmemResizeLock);
}
+
+ /*
+ * TODO: Shouldn't we call ResizeBufferPool() here as well? Or those
+ * backend who can not lock the LWLock conditionally won't resize the
+ * buffers.
+ */
}
return true;
@@ -1138,13 +1145,17 @@ ProcessBarrierShmemResize(Barrier *barrier)
{
Assert(IsUnderPostmaster);
- elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d",
- NBuffersOld, NBuffersPending, pending_pm_shmem_resize);
+ elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d, %d",
+ NBuffersOld, NBuffersPending, pending_pm_shmem_resize, delay_shmem_resize);
/* Wait until we have seen the new NBuffers value */
if (!pending_pm_shmem_resize)
return false;
+ /* Wait till this process becomes ready to resize buffers. */
+ if (delay_shmem_resize)
+ return false;
+
/*
* First thing to do after attaching to the barrier is to wait for others.
* We can't simply use BarrierArriveAndWait, because backends might arrive
@@ -1195,6 +1206,15 @@ ProcessBarrierShmemResize(Barrier *barrier)
/* The second phase means the resize has finished, SHMEM_RESIZE_DONE */
BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_DONE);
+ if (MyBackendType == B_BG_WRITER)
+ {
+ /*
+ * Before resuming regular background writer activity, adjust the
+ * statistics collected so far.
+ */
+ BgBufferSyncAdjust(NBuffersOld, NBuffers);
+ }
+
BarrierDetach(barrier);
return true;
}
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 72f5acceec7..32b34f28ead 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -233,7 +233,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
/*
* Do one cycle of dirty-buffer writing.
*/
- can_hibernate = BgBufferSync(&wb_context);
+ can_hibernate = BgBufferSync(&wb_context, false);
/* Report pending statistics to the cumulative stats system */
pgstat_report_bgwriter();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 6f5743036a2..62c1672fb70 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -164,8 +164,15 @@ BufferManagerShmemInit(int FirstBufferToInit)
if (FirstBufferToInit < NBuffers)
GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
- /* Init other shared buffer-management stuff */
- StrategyInitialize(!foundDescs);
+ /*
+ * Init other shared buffer-management stuff from scratch configuring buffer
+ * pool the first time. If we are just resizing buffer pool adjust only the
+ * required structures.
+ */
+ if (FirstBufferToInit == 0)
+ StrategyInitialize(!foundDescs);
+ else
+ StrategyReInitialize(FirstBufferToInit);
/* Initialize per-backend file flush context */
WritebackContextInit(&BackendWritebackContext,
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 169a44dd9fc..590fc737da8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3611,6 +3611,32 @@ BufferSync(int flags)
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_scan);
}
+/*
+ * Information saved between BgBufferSync() calls so we can determine the
+ * strategy point's advance rate and avoid scanning already-cleaned buffers. The
+ * variables are global instead of static local so that BgBufferSyncAdjust() can
+ * adjust it when resizing shared buffers.
+ */
+static bool saved_info_valid = false;
+static int prev_strategy_buf_id;
+static uint32 prev_strategy_passes;
+static int next_to_clean;
+static uint32 next_passes;
+
+/* Moving averages of allocation rate and clean-buffer density */
+static float smoothed_alloc = 0;
+static float smoothed_density = 10.0;
+
+void
+BgBufferSyncAdjust(int NBuffersOld, int NBuffersNew)
+{
+ saved_info_valid = false;
+#ifdef BGW_DEBUG
+ elog(DEBUG2, "invalidated background writer status after resizing buffers from %d to %d",
+ NBuffersOld, NBuffersNew);
+#endif
+}
+
/*
* BgBufferSync -- Write out some dirty buffers in the pool.
*
@@ -3623,27 +3649,13 @@ BufferSync(int flags)
* bgwriter_lru_maxpages to 0.)
*/
bool
-BgBufferSync(WritebackContext *wb_context)
+BgBufferSync(WritebackContext *wb_context, bool reset)
{
/* info obtained from freelist.c */
int strategy_buf_id;
uint32 strategy_passes;
uint32 recent_alloc;
- /*
- * Information saved between calls so we can determine the strategy
- * point's advance rate and avoid scanning already-cleaned buffers.
- */
- static bool saved_info_valid = false;
- static int prev_strategy_buf_id;
- static uint32 prev_strategy_passes;
- static int next_to_clean;
- static uint32 next_passes;
-
- /* Moving averages of allocation rate and clean-buffer density */
- static float smoothed_alloc = 0;
- static float smoothed_density = 10.0;
-
/* Potentially these could be tunables, but for now, not */
float smoothing_samples = 16;
float scan_whole_pool_milliseconds = 120000.0;
@@ -3666,6 +3678,22 @@ BgBufferSync(WritebackContext *wb_context)
long new_strategy_delta;
uint32 new_recent_alloc;
+ /*
+ * If buffer pool is being shrunk the buffer being written out may not remain
+ * valid. If the buffer pool is being expanded, more buffers will become
+ * available without even this function writing out any. Hence wait till
+ * buffer resizing finishes i.e. go into hibernation mode.
+ */
+ if (pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) != NBuffers)
+ return true;
+
+ /*
+ * Resizing shared buffers while this function is performing an LRU scan on
+ * them may lead to wrong results. Indicate that the resizing should wait for
+ * the LRU scan to complete.
+ */
+ delay_shmem_resize = true;
+
/*
* Find out where the freelist clock sweep currently is, and how many
* buffer allocations have happened since our last call.
@@ -3842,8 +3870,17 @@ BgBufferSync(WritebackContext *wb_context)
num_written = 0;
reusable_buffers = reusable_buffers_est;
- /* Execute the LRU scan */
- while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)
+ /*
+ * Execute the LRU scan.
+ *
+ * If buffer pool is being shrunk, the buffer being written may not remain
+ * valid. If the buffer pool is being expanded, more buffers will become
+ * available without even this function writing any. Hence stop what we are doing. This
+ * also unblocks other processes that are waiting for buffer resizing to
+ * finish.
+ */
+ while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est &&
+ pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) == NBuffers)
{
int sync_state = SyncOneBuffer(next_to_clean, true,
wb_context);
@@ -3902,6 +3939,9 @@ BgBufferSync(WritebackContext *wb_context)
#endif
}
+ /* Let the resizing commence. */
+ delay_shmem_resize = false;
+
/* Return true if OK to hibernate */
return (bufs_to_lap == 0 && recent_alloc == 0);
}
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 7b9ed010e2f..41641bb3ae6 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -98,6 +98,9 @@ static BufferDesc *GetBufferFromRing(BufferAccessStrategy strategy,
uint32 *buf_state);
static void AddBufferToRing(BufferAccessStrategy strategy,
BufferDesc *buf);
+#ifdef USE_ASSERT_CHECKING
+static void StrategyValidateFreeList(void);
+#endif /* USE_ASSERT_CHECKING */
/*
* ClockSweepTick - Helper routine for StrategyGetBuffer()
@@ -526,6 +529,88 @@ StrategyInitialize(bool init)
Assert(!init);
}
+/*
+ * StrategyReInitialize -- re-initialize the buffer cache replacement
+ * strategy.
+ *
+ * To be called when resizing buffer manager and only from the coordinator.
+ * TODO: Assess the differences between this function and StrategyInitialize().
+ */
+void
+StrategyReInitialize(int FirstBufferIdToInit)
+{
+ bool found;
+
+ /*
+ * Resizing memory for buffer pools should not affect the address of
+ * StrategyControl.
+ */
+ if (StrategyControl != (BufferStrategyControl *)
+ ShmemInitStructInSegment("Buffer Strategy Status",
+ sizeof(BufferStrategyControl),
+ &found, STRATEGY_SHMEM_SEGMENT))
+ elog(FATAL, "something went wrong while re-initializing the buffer strategy");
+
+ Assert(found);
+
+ /* TODO: Buffer lookup table adjustment: There are two options:
+ *
+ * 1. Resize the buffer lookup table to match the new number of buffers. But
+ * this requires rehashing all the entries in the buffer lookup table with
+ * the new table size.
+ *
+ * 2. Allocate maximum size of the buffer lookup table at the beginning and
+ * never resize it. This leaves sparse buffer lookup table which is
+ * inefficient from both memory and time perspective. According to David
+ * Rowley, the sparse entries in the buffer look up table cause frequent
+ * cacheline reload which affect performance. If the impact of that
+ * inefficiency in a benchmark is significant, we will need to consider first
+ * option.
+ */
+
+ /*
+ * When shrinking buffers, we must have adjusted the first and the last free
+ * buffer when removing the buffers being shrunk from the free list. Nothing
+ * to be done here.
+ *
+ * When expanding the shared buffers, new buffers are added at the end of the
+ * freelist or they form the new free list if there are no free buffers.
+ */
+ if (FirstBufferIdToInit < NBuffers)
+ {
+ if (StrategyControl->firstFreeBuffer == FREENEXT_END_OF_LIST)
+ StrategyControl->firstFreeBuffer = FirstBufferIdToInit;
+ else
+ {
+ Assert(StrategyControl->lastFreeBuffer >= 0);
+ GetBufferDescriptor(StrategyControl->lastFreeBuffer - 1)->freeNext = FirstBufferIdToInit;
+ }
+
+ StrategyControl->lastFreeBuffer = NBuffers - 1;
+ }
+
+ /* Check free list sanity after resizing. */
+#ifdef USE_ASSERT_CHECKING
+ StrategyValidateFreeList();
+#endif /* USE_ASSERT_CHECKING */
+
+ /*
+ * The clock sweep tick pointer might have got invalidated. Reset it as if
+ * starting a fresh server.
+ */
+ pg_atomic_write_u32(&StrategyControl->nextVictimBuffer, 0);
+
+ /*
+ * The old statistics is viewed in the context of the number of shared
+ * buffers. It does not make sense now that the number of shared buffers
+ * itself has changed.
+ */
+ StrategyControl->completePasses = 0;
+ pg_atomic_init_u32(&StrategyControl->numBufferAllocs, 0);
+
+ /* No pending notification */
+ StrategyControl->bgwprocno = -1;
+}
/*
* StrategyPurgeFreeList -- remove all buffers with id higher than the number of
@@ -595,6 +680,54 @@ StrategyPurgeFreeList(int numBuffers)
*/
}
+#ifdef USE_ASSERT_CHECKING
+/*
+ * StrategyValidateFreeList-- check sanity of free buffer list.
+ */
+static void
+StrategyValidateFreeList(void)
+{
+ int nextFree = StrategyControl->firstFreeBuffer;
+ int numFreeBuffers = 0;
+ int lastFreeBuffer = FREENEXT_END_OF_LIST;
+
+ SpinLockAcquire(&StrategyControl->buffer_strategy_lock);
+
+ while (nextFree != FREENEXT_END_OF_LIST)
+ {
+ BufferDesc *buf = GetBufferDescriptor(nextFree);
+
+ /* nextFree should be id of buffer being examined. */
+ Assert(nextFree == buf->buf_id);
+ Assert(buf->buf_id < NBuffers);
+ /* The buffer should not be marked as not in the list. */
+ Assert(buf->freeNext != FREENEXT_NOT_IN_LIST);
+
+ /* Update our knowledge of last buffer in the free list. */
+ lastFreeBuffer = buf->buf_id;
+
+ numFreeBuffers++;
+
+ /* Avoid infinite recursion in case there are cycles in free list. */
+ if (numFreeBuffers > NBuffers)
+ break;
+
+ nextFree = buf->freeNext;
+ }
+
+ Assert(numFreeBuffers <= NBuffers);
+
+ /*
+ * Make sure that the StrategyControl's knowledge of last free buffer
+ * agrees with what's there in the free list.
+ */
+ if (StrategyControl->firstFreeBuffer != FREENEXT_END_OF_LIST)
+ Assert(StrategyControl->lastFreeBuffer == lastFreeBuffer);
+
+ SpinLockRelease(&StrategyControl->buffer_strategy_lock);
+}
+#endif /* USE_ASSERT_CHECKING */
+
/* ----------------------------------------------------------------
* Backend-private buffer ring management
* ----------------------------------------------------------------
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index add15e3723b..46949e9d90e 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -454,6 +454,7 @@ extern void StrategyNotifyBgWriter(int bgwprocno);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);
extern void StrategyPurgeFreeList(int numBuffers);
+extern void StrategyReInitialize(int FirstBufferToInit);
extern bool have_free_buffer(void);
/* buf_table.c */
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 0c554f0b130..83a75eab844 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -298,7 +298,8 @@ extern bool ConditionalLockBufferForCleanup(Buffer buffer);
extern bool IsBufferCleanupOK(Buffer buffer);
extern bool HoldingBufferPinThatDelaysRecovery(void);
-extern bool BgBufferSync(struct WritebackContext *wb_context);
+extern bool BgBufferSync(struct WritebackContext *wb_context, bool reset);
+extern void BgBufferSyncAdjust(int NBuffersOld, int NBuffersNew);
extern uint32 GetPinLimit(void);
extern uint32 GetLocalPinLimit(void);
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index bb7ae4d33b3..7d1c64a9267 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -65,6 +65,7 @@ typedef void (*shmem_startup_hook_type) (void);
extern PGDLLIMPORT bool proc_exit_inprogress;
extern PGDLLIMPORT bool shmem_exit_inprogress;
extern PGDLLIMPORT volatile bool pending_pm_shmem_resize;
+extern PGDLLIMPORT volatile bool delay_shmem_resize;
pg_noreturn extern void proc_exit(int code);
extern void shmem_exit(int code);
--
2.49.0
From 25816411c7a77a87b8527a901633865f1c1056b7 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Wed, 11 Jun 2025 18:15:06 +0530
Subject: [PATCH v5 10/10] Additional validation for buffer in the ring
If the buffer pool has been shrunk, the buffers in the buffer list may
not be valid anymore. Modify GetBufferFromRing to check if the buffer is
still valid before using it. This makes GetBufferFromRing() a bit more
expensive because of additional boolean condition. That may not be
expensive enough to affect query performance. The alternative to that is
more complex as explained below.
The strategy object is created in CurrentMemoryContext and is not
available in any global structure thus accessible when processing buffer
resizing barriers. We may modify GetAccessStrategy() to register
strategy in a global linked list and then arrange to deregister it once
it's no more in use. Looking at the places which use
GetAccessStrategy(), fixing all those may be some work.
Ashutosh Bapat
---
src/backend/storage/buffer/freelist.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 41641bb3ae6..74d070733a4 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -948,12 +948,13 @@ GetBufferFromRing(BufferAccessStrategy strategy, uint32 *buf_state)
strategy->current = 0;
/*
- * If the slot hasn't been filled yet, tell the caller to allocate a new
- * buffer with the normal allocation strategy. He will then fill this
- * slot by calling AddBufferToRing with the new buffer.
+ * If the slot hasn't been filled yet or the buffer in the slot has been
+ * invalidated when buffer pool was shrunk, tell the caller to allocate a new
+ * buffer with the normal allocation strategy. He will then fill this slot
+ * by calling AddBufferToRing with the new buffer.
*/
bufnum = strategy->buffers[strategy->current];
- if (bufnum == InvalidBuffer)
+ if (bufnum == InvalidBuffer || bufnum > NBuffers)
return NULL;
/*
--
2.49.0
Attachments:
[text/plain] v5-0001-Process-config-reload-in-AIO-workers.patch (1.8K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/2-v5-0001-Process-config-reload-in-AIO-workers.patch)
download | inline diff:
From 5d4f46dc13bacf9c1df79233f8e4017a9dcd6919 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 15:14:33 +0200
Subject: [PATCH v5 01/10] Process config reload in AIO workers
Currenly AIO workers process interrupts only via CHECK_FOR_INTERRUPTS,
which does not include ConfigReloadPending. Thus we need to check for it
explicitly.
---
src/backend/storage/aio/method_worker.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/src/backend/storage/aio/method_worker.c b/src/backend/storage/aio/method_worker.c
index 36be179678d..b4d5c46fb94 100644
--- a/src/backend/storage/aio/method_worker.c
+++ b/src/backend/storage/aio/method_worker.c
@@ -80,6 +80,7 @@ static void pgaio_worker_shmem_init(bool first_time);
static bool pgaio_worker_needs_synchronous_execution(PgAioHandle *ioh);
static int pgaio_worker_submit(uint16 num_staged_ios, PgAioHandle **staged_ios);
+static void pgaio_worker_process_interrupts(void);
const IoMethodOps pgaio_worker_ops = {
.shmem_size = pgaio_worker_shmem_size,
@@ -461,6 +462,8 @@ IoWorkerMain(const void *startup_data, size_t startup_data_len)
int nwakeups = 0;
int worker;
+ pgaio_worker_process_interrupts();
+
/*
* Try to get a job to do.
*
@@ -584,3 +587,25 @@ pgaio_workers_enabled(void)
{
return io_method == IOMETHOD_WORKER;
}
+
+/*
+ * Process any new interrupts.
+ */
+static void
+pgaio_worker_process_interrupts(void)
+{
+ /*
+ * Reloading config can trigger further signals, complicating interrupts
+ * processing -- so let it run first.
+ *
+ * XXX: Is there any need in memory barrier after ProcessConfigFile?
+ */
+ if (ConfigReloadPending)
+ {
+ ConfigReloadPending = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ }
+
+ if (ProcSignalBarrierPending)
+ ProcessProcSignalBarrier();
+}
--
2.49.0
[text/plain] v5-0002-Introduce-pending-flag-for-GUC-assign-hooks.patch (12.8K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/3-v5-0002-Introduce-pending-flag-for-GUC-assign-hooks.patch)
download | inline diff:
From fd29084b3221e1901a1f07656d4e7abb31335caf Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Sun, 6 Apr 2025 16:40:32 +0200
Subject: [PATCH v5 02/10] Introduce pending flag for GUC assign hooks
Currently an assing hook can perform some preprocessing of a new value,
but it cannot change the behavior, which dictates that the new value
will be applied immediately after the hook. Certain GUC options (like
shared_buffers, coming in subsequent patches) may need coordinating work
between backends to change, meaning we cannot apply it right away.
Add a new flag "pending" for an assign hook to allow the hook indicate
exactly that. If the pending flag is set after the hook, the new value
will not be applied and it's handling becomes the hook's implementation
responsibility.
Note, that this also requires changes in the way how GUCs are getting
reported, but the patch does not cover that yet.
---
src/backend/access/transam/xlog.c | 2 +-
src/backend/commands/variable.c | 6 +--
src/backend/libpq/pqcomm.c | 8 ++--
src/backend/tcop/postgres.c | 2 +-
src/backend/utils/misc/guc.c | 59 +++++++++++++++++++---------
src/backend/utils/misc/stack_depth.c | 2 +-
src/include/utils/guc.h | 2 +-
src/include/utils/guc_hooks.h | 20 +++++-----
8 files changed, 61 insertions(+), 40 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 47ffc0a2307..d1be780683b 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2321,7 +2321,7 @@ CalculateCheckpointSegments(void)
}
void
-assign_max_wal_size(int newval, void *extra)
+assign_max_wal_size(int newval, void *extra, bool *pending)
{
max_wal_size_mb = newval;
CalculateCheckpointSegments();
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 608f10d9412..e40dae2ddf2 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -1143,7 +1143,7 @@ check_cluster_name(char **newval, void **extra, GucSource source)
* GUC assign_hook for maintenance_io_concurrency
*/
void
-assign_maintenance_io_concurrency(int newval, void *extra)
+assign_maintenance_io_concurrency(int newval, void *extra, bool *pending)
{
/*
* Reconfigure recovery prefetching, because a setting it depends on
@@ -1161,12 +1161,12 @@ assign_maintenance_io_concurrency(int newval, void *extra)
* they may be assigned in either order.
*/
void
-assign_io_max_combine_limit(int newval, void *extra)
+assign_io_max_combine_limit(int newval, void *extra, bool *pending)
{
io_combine_limit = Min(newval, io_combine_limit_guc);
}
void
-assign_io_combine_limit(int newval, void *extra)
+assign_io_combine_limit(int newval, void *extra, bool *pending)
{
io_combine_limit = Min(io_max_combine_limit, newval);
}
diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index e5171467de1..2a6a587ef76 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -1952,7 +1952,7 @@ pq_settcpusertimeout(int timeout, Port *port)
* GUC assign_hook for tcp_keepalives_idle
*/
void
-assign_tcp_keepalives_idle(int newval, void *extra)
+assign_tcp_keepalives_idle(int newval, void *extra, bool *pending)
{
/*
* The kernel API provides no way to test a value without setting it; and
@@ -1985,7 +1985,7 @@ show_tcp_keepalives_idle(void)
* GUC assign_hook for tcp_keepalives_interval
*/
void
-assign_tcp_keepalives_interval(int newval, void *extra)
+assign_tcp_keepalives_interval(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_setkeepalivesinterval(newval, MyProcPort);
@@ -2008,7 +2008,7 @@ show_tcp_keepalives_interval(void)
* GUC assign_hook for tcp_keepalives_count
*/
void
-assign_tcp_keepalives_count(int newval, void *extra)
+assign_tcp_keepalives_count(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_setkeepalivescount(newval, MyProcPort);
@@ -2031,7 +2031,7 @@ show_tcp_keepalives_count(void)
* GUC assign_hook for tcp_user_timeout
*/
void
-assign_tcp_user_timeout(int newval, void *extra)
+assign_tcp_user_timeout(int newval, void *extra, bool *pending)
{
/* See comments in assign_tcp_keepalives_idle */
(void) pq_settcpusertimeout(newval, MyProcPort);
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 2f8c3d5f918..0d1b6466d1e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3591,7 +3591,7 @@ check_log_stats(bool *newval, void **extra, GucSource source)
/* GUC assign hook for transaction_timeout */
void
-assign_transaction_timeout(int newval, void *extra)
+assign_transaction_timeout(int newval, void *extra, bool *pending)
{
if (IsTransactionState())
{
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 667df448732..bb681f5bc60 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1679,6 +1679,7 @@ InitializeOneGUCOption(struct config_generic *gconf)
struct config_int *conf = (struct config_int *) gconf;
int newval = conf->boot_val;
void *extra = NULL;
+ bool pending = false;
Assert(newval >= conf->min);
Assert(newval <= conf->max);
@@ -1687,9 +1688,13 @@ InitializeOneGUCOption(struct config_generic *gconf)
elog(FATAL, "failed to initialize %s to %d",
conf->gen.name, newval);
if (conf->assign_hook)
- conf->assign_hook(newval, extra);
- *conf->variable = conf->reset_val = newval;
- conf->gen.extra = conf->reset_extra = extra;
+ conf->assign_hook(newval, extra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = conf->reset_val = newval;
+ conf->gen.extra = conf->reset_extra = extra;
+ }
break;
}
case PGC_REAL:
@@ -2041,13 +2046,18 @@ ResetAllOptions(void)
case PGC_INT:
{
struct config_int *conf = (struct config_int *) gconf;
+ bool pending = false;
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
- conf->reset_extra);
- *conf->variable = conf->reset_val;
- set_extra_field(&conf->gen, &conf->gen.extra,
- conf->reset_extra);
+ conf->reset_extra,
+ &pending);
+ if (!pending)
+ {
+ *conf->variable = conf->reset_val;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ conf->reset_extra);
+ }
break;
}
case PGC_REAL:
@@ -2424,16 +2434,21 @@ AtEOXact_GUC(bool isCommit, int nestLevel)
struct config_int *conf = (struct config_int *) gconf;
int newval = newvalue.val.intval;
void *newextra = newvalue.extra;
+ bool pending = false;
if (*conf->variable != newval ||
conf->gen.extra != newextra)
{
if (conf->assign_hook)
- conf->assign_hook(newval, newextra);
- *conf->variable = newval;
- set_extra_field(&conf->gen, &conf->gen.extra,
- newextra);
- changed = true;
+ conf->assign_hook(newval, newextra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = newval;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ newextra);
+ changed = true;
+ }
}
break;
}
@@ -3850,18 +3865,24 @@ set_config_with_handle(const char *name, config_handle *handle,
if (changeVal)
{
+ bool pending = false;
+
/* Save old value to support transaction abort */
if (!makeDefault)
push_old_value(&conf->gen, action);
if (conf->assign_hook)
- conf->assign_hook(newval, newextra);
- *conf->variable = newval;
- set_extra_field(&conf->gen, &conf->gen.extra,
- newextra);
- set_guc_source(&conf->gen, source);
- conf->gen.scontext = context;
- conf->gen.srole = srole;
+ conf->assign_hook(newval, newextra, &pending);
+
+ if (!pending)
+ {
+ *conf->variable = newval;
+ set_extra_field(&conf->gen, &conf->gen.extra,
+ newextra);
+ set_guc_source(&conf->gen, source);
+ conf->gen.scontext = context;
+ conf->gen.srole = srole;
+ }
}
if (makeDefault)
{
diff --git a/src/backend/utils/misc/stack_depth.c b/src/backend/utils/misc/stack_depth.c
index 8f7cf531fbc..ef59ae62008 100644
--- a/src/backend/utils/misc/stack_depth.c
+++ b/src/backend/utils/misc/stack_depth.c
@@ -156,7 +156,7 @@ check_max_stack_depth(int *newval, void **extra, GucSource source)
/* GUC assign hook for max_stack_depth */
void
-assign_max_stack_depth(int newval, void *extra)
+assign_max_stack_depth(int newval, void *extra, bool *pending)
{
ssize_t newval_bytes = newval * (ssize_t) 1024;
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index f619100467d..8802ad8a3cb 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -187,7 +187,7 @@ typedef bool (*GucStringCheckHook) (char **newval, void **extra, GucSource sourc
typedef bool (*GucEnumCheckHook) (int *newval, void **extra, GucSource source);
typedef void (*GucBoolAssignHook) (bool newval, void *extra);
-typedef void (*GucIntAssignHook) (int newval, void *extra);
+typedef void (*GucIntAssignHook) (int newval, void *extra, bool *pending);
typedef void (*GucRealAssignHook) (double newval, void *extra);
typedef void (*GucStringAssignHook) (const char *newval, void *extra);
typedef void (*GucEnumAssignHook) (int newval, void *extra);
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index 799fa7ace68..c8300cffa8e 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -81,14 +81,14 @@ extern bool check_log_stats(bool *newval, void **extra, GucSource source);
extern bool check_log_timezone(char **newval, void **extra, GucSource source);
extern void assign_log_timezone(const char *newval, void *extra);
extern const char *show_log_timezone(void);
-extern void assign_maintenance_io_concurrency(int newval, void *extra);
-extern void assign_io_max_combine_limit(int newval, void *extra);
-extern void assign_io_combine_limit(int newval, void *extra);
+extern void assign_maintenance_io_concurrency(int newval, void *extra, bool *pending);
+extern void assign_io_max_combine_limit(int newval, void *extra, bool *pending);
+extern void assign_io_combine_limit(int newval, void *extra, bool *pending);
extern bool check_max_slot_wal_keep_size(int *newval, void **extra,
GucSource source);
-extern void assign_max_wal_size(int newval, void *extra);
+extern void assign_max_wal_size(int newval, void *extra, bool *pending);
extern bool check_max_stack_depth(int *newval, void **extra, GucSource source);
-extern void assign_max_stack_depth(int newval, void *extra);
+extern void assign_max_stack_depth(int newval, void *extra, bool *pending);
extern bool check_multixact_member_buffers(int *newval, void **extra,
GucSource source);
extern bool check_multixact_offset_buffers(int *newval, void **extra,
@@ -143,13 +143,13 @@ extern void assign_synchronous_standby_names(const char *newval, void *extra);
extern void assign_synchronous_commit(int newval, void *extra);
extern void assign_syslog_facility(int newval, void *extra);
extern void assign_syslog_ident(const char *newval, void *extra);
-extern void assign_tcp_keepalives_count(int newval, void *extra);
+extern void assign_tcp_keepalives_count(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_count(void);
-extern void assign_tcp_keepalives_idle(int newval, void *extra);
+extern void assign_tcp_keepalives_idle(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_idle(void);
-extern void assign_tcp_keepalives_interval(int newval, void *extra);
+extern void assign_tcp_keepalives_interval(int newval, void *extra, bool *pending);
extern const char *show_tcp_keepalives_interval(void);
-extern void assign_tcp_user_timeout(int newval, void *extra);
+extern void assign_tcp_user_timeout(int newval, void *extra, bool *pending);
extern const char *show_tcp_user_timeout(void);
extern bool check_temp_buffers(int *newval, void **extra, GucSource source);
extern bool check_temp_tablespaces(char **newval, void **extra,
@@ -165,7 +165,7 @@ extern bool check_transaction_buffers(int *newval, void **extra, GucSource sourc
extern bool check_transaction_deferrable(bool *newval, void **extra, GucSource source);
extern bool check_transaction_isolation(int *newval, void **extra, GucSource source);
extern bool check_transaction_read_only(bool *newval, void **extra, GucSource source);
-extern void assign_transaction_timeout(int newval, void *extra);
+extern void assign_transaction_timeout(int newval, void *extra, bool *pending);
extern const char *show_unix_socket_permissions(void);
extern bool check_wal_buffers(int *newval, void **extra, GucSource source);
extern bool check_wal_consistency_checking(char **newval, void **extra,
--
2.49.0
[text/plain] v5-0003-Introduce-pss_barrierReceivedGeneration.patch (7.3K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/4-v5-0003-Introduce-pss_barrierReceivedGeneration.patch)
download | inline diff:
From efbe93b30e0174c4fba42047b14208b3fd5c0f43 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Fri, 4 Apr 2025 21:46:14 +0200
Subject: [PATCH v5 03/10] Introduce pss_barrierReceivedGeneration
Currently WaitForProcSignalBarrier allows to make sure the message sent
via EmitProcSignalBarrier was processed by all ProcSignal mechanism
participants.
Add pss_barrierReceivedGeneration alongside with pss_barrierGeneration,
which will be updated when a process has received the message, but not
processed it yet. This makes it possible to support a new mode of
waiting, when ProcSignal participants want to synchronize message
processing. To do that, a participant can wait via
WaitForProcSignalBarrierReceived when processing a message, effectively
making sure that all processes are going to start processing
ProcSignalBarrier simultaneously.
---
src/backend/storage/ipc/procsignal.c | 67 ++++++++++++++++++++++------
src/include/storage/procsignal.h | 1 +
2 files changed, 54 insertions(+), 14 deletions(-)
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index a9bb540b55a..c6bec9be423 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -58,7 +58,10 @@
* of it. For such use cases, we set a bit in pss_barrierCheckMask and then
* increment the current "barrier generation"; when the new barrier generation
* (or greater) appears in the pss_barrierGeneration flag of every process,
- * we know that the message has been received everywhere.
+ * we know that the message has been received and processed everywhere. In case
+ * if we only need to know only that the message was received everywhere (e.g.
+ * receiving processes need to handle the message in a coordinated fashion)
+ * use pss_barrierReceivedGeneration in the same way.
*/
typedef struct
{
@@ -70,6 +73,7 @@ typedef struct
/* Barrier-related fields (not protected by pss_mutex) */
pg_atomic_uint64 pss_barrierGeneration;
+ pg_atomic_uint64 pss_barrierReceivedGeneration;
pg_atomic_uint32 pss_barrierCheckMask;
ConditionVariable pss_barrierCV;
} ProcSignalSlot;
@@ -152,6 +156,8 @@ ProcSignalShmemInit(void)
slot->pss_cancel_key_len = 0;
MemSet(slot->pss_signalFlags, 0, sizeof(slot->pss_signalFlags));
pg_atomic_init_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
+ pg_atomic_init_u64(&slot->pss_barrierReceivedGeneration,
+ PG_UINT64_MAX);
pg_atomic_init_u32(&slot->pss_barrierCheckMask, 0);
ConditionVariableInit(&slot->pss_barrierCV);
}
@@ -199,6 +205,8 @@ ProcSignalInit(const uint8 *cancel_key, int cancel_key_len)
barrier_generation =
pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration);
pg_atomic_write_u64(&slot->pss_barrierGeneration, barrier_generation);
+ pg_atomic_write_u64(&slot->pss_barrierReceivedGeneration,
+ barrier_generation);
if (cancel_key_len > 0)
memcpy(slot->pss_cancel_key, cancel_key, cancel_key_len);
@@ -263,6 +271,7 @@ CleanupProcSignalState(int status, Datum arg)
* no barrier waits block on it.
*/
pg_atomic_write_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
+ pg_atomic_write_u64(&slot->pss_barrierReceivedGeneration, PG_UINT64_MAX);
SpinLockRelease(&slot->pss_mutex);
@@ -416,12 +425,8 @@ EmitProcSignalBarrier(ProcSignalBarrierType type)
return generation;
}
-/*
- * WaitForProcSignalBarrier - wait until it is guaranteed that all changes
- * requested by a specific call to EmitProcSignalBarrier() have taken effect.
- */
-void
-WaitForProcSignalBarrier(uint64 generation)
+static void
+WaitForProcSignalBarrierInternal(uint64 generation, bool receivedOnly)
{
Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));
@@ -436,12 +441,17 @@ WaitForProcSignalBarrier(uint64 generation)
uint64 oldval;
/*
- * It's important that we check only pss_barrierGeneration here and
- * not pss_barrierCheckMask. Bits in pss_barrierCheckMask get cleared
- * before the barrier is actually absorbed, but pss_barrierGeneration
+ * It's important that we check only pss_barrierGeneration &
+ * pss_barrierGeneration here and not pss_barrierCheckMask. Bits in
+ * pss_barrierCheckMask get cleared before the barrier is actually
+ * absorbed, but pss_barrierGeneration & pss_barrierReceivedGeneration
* is updated only afterward.
*/
- oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+ if (receivedOnly)
+ oldval = pg_atomic_read_u64(&slot->pss_barrierReceivedGeneration);
+ else
+ oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+
while (oldval < generation)
{
if (ConditionVariableTimedSleep(&slot->pss_barrierCV,
@@ -450,7 +460,11 @@ WaitForProcSignalBarrier(uint64 generation)
ereport(LOG,
(errmsg("still waiting for backend with PID %d to accept ProcSignalBarrier",
(int) pg_atomic_read_u32(&slot->pss_pid))));
- oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
+
+ if (receivedOnly)
+ oldval = pg_atomic_read_u64(&slot->pss_barrierReceivedGeneration);
+ else
+ oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
}
ConditionVariableCancelSleep();
}
@@ -464,12 +478,33 @@ WaitForProcSignalBarrier(uint64 generation)
* The caller is probably calling this function because it wants to read
* the shared state or perform further writes to shared state once all
* backends are known to have absorbed the barrier. However, the read of
- * pss_barrierGeneration was performed unlocked; insert a memory barrier
- * to separate it from whatever follows.
+ * pss_barrierGeneration & pss_barrierReceivedGeneration was performed
+ * unlocked; insert a memory barrier to separate it from whatever follows.
*/
pg_memory_barrier();
}
+/*
+ * WaitForProcSignalBarrier - wait until it is guaranteed that all changes
+ * requested by a specific call to EmitProcSignalBarrier() have taken effect.
+ */
+void
+WaitForProcSignalBarrier(uint64 generation)
+{
+ WaitForProcSignalBarrierInternal(generation, false);
+}
+
+/*
+ * WaitForProcSignalBarrierReceived - wait until it is guaranteed that all
+ * backends have observed the message sent by a specific call to
+ * EmitProcSignalBarrier().
+ */
+void
+WaitForProcSignalBarrierReceived(uint64 generation)
+{
+ WaitForProcSignalBarrierInternal(generation, true);
+}
+
/*
* Handle receipt of an interrupt indicating a global barrier event.
*
@@ -523,6 +558,10 @@ ProcessProcSignalBarrier(void)
if (local_gen == shared_gen)
return;
+ /* The message is observed, record that */
+ pg_atomic_write_u64(&MyProcSignalSlot->pss_barrierReceivedGeneration,
+ shared_gen);
+
/*
* Get and clear the flags that are set for this backend. Note that
* pg_atomic_exchange_u32 is a full barrier, so we're guaranteed that the
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index afeeb1ca019..2733bbb8c5b 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -79,6 +79,7 @@ extern void SendCancelRequest(int backendPID, const uint8 *cancel_key, int cance
extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
extern void WaitForProcSignalBarrier(uint64 generation);
+extern void WaitForProcSignalBarrierReceived(uint64 generation);
extern void ProcessProcSignalBarrier(void);
extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
--
2.49.0
[text/plain] v5-0004-Allow-to-use-multiple-shared-memory-mappings.patch (30.5K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/5-v5-0004-Allow-to-use-multiple-shared-memory-mappings.patch)
download | inline diff:
From a8e77ba00c05765f6d7ed05c8239a6bfecdbce4c Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Fri, 28 Feb 2025 19:54:47 +0100
Subject: [PATCH v5 04/10] Allow to use multiple shared memory mappings
Currently all the work with shared memory is done via a single anonymous
memory mapping, which limits ways how the shared memory could be organized.
Introduce possibility to allocate multiple shared memory mappings, where
a single mapping is associated with a specified shared memory segment.
There is only fixed amount of available segments, currently only one
main shared memory segment is allocated. A new shared memory API is
introduces, extended with a segment as a new parameter. As a path of
least resistance, the original API is kept in place, utilizing the main
shared memory segment.
---
src/backend/port/posix_sema.c | 4 +-
src/backend/port/sysv_sema.c | 4 +-
src/backend/port/sysv_shmem.c | 138 +++++++++++++++++++---------
src/backend/port/win32_sema.c | 2 +-
src/backend/storage/ipc/ipc.c | 4 +-
src/backend/storage/ipc/ipci.c | 63 +++++++------
src/backend/storage/ipc/shmem.c | 148 +++++++++++++++++++++---------
src/backend/storage/lmgr/lwlock.c | 13 ++-
src/include/storage/ipc.h | 2 +-
src/include/storage/pg_sema.h | 2 +-
src/include/storage/pg_shmem.h | 18 ++++
src/include/storage/shmem.h | 12 +++
12 files changed, 284 insertions(+), 126 deletions(-)
diff --git a/src/backend/port/posix_sema.c b/src/backend/port/posix_sema.c
index 269c7460817..401e1113fa1 100644
--- a/src/backend/port/posix_sema.c
+++ b/src/backend/port/posix_sema.c
@@ -193,7 +193,7 @@ PGSemaphoreShmemSize(int maxSemas)
* we don't have to expose the counters to other processes.)
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
struct stat statbuf;
@@ -220,7 +220,7 @@ PGReserveSemaphores(int maxSemas)
* ShmemAlloc() won't be ready yet.
*/
sharedSemas = (PGSemaphore)
- ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+ ShmemAllocUnlockedInSegment(PGSemaphoreShmemSize(maxSemas), shmem_segment);
#endif
numSems = 0;
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
index 423b2b4f9d6..4ce2cfb662b 100644
--- a/src/backend/port/sysv_sema.c
+++ b/src/backend/port/sysv_sema.c
@@ -307,7 +307,7 @@ PGSemaphoreShmemSize(int maxSemas)
* have clobbered.)
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
struct stat statbuf;
@@ -328,7 +328,7 @@ PGReserveSemaphores(int maxSemas)
* ShmemAlloc() won't be ready yet.
*/
sharedSemas = (PGSemaphore)
- ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+ ShmemAllocUnlockedInSegment(PGSemaphoreShmemSize(maxSemas), shmem_segment);
numSharedSemas = 0;
maxSharedSemas = maxSemas;
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 197926d44f6..56af0231d24 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -94,8 +94,19 @@ typedef enum
unsigned long UsedShmemSegID = 0;
void *UsedShmemSegAddr = NULL;
-static Size AnonymousShmemSize;
-static void *AnonymousShmem = NULL;
+typedef struct AnonymousMapping
+{
+ int shmem_segment;
+ Size shmem_size; /* Size of the mapping */
+ Pointer shmem; /* Pointer to the start of the mapped memory */
+ Pointer seg_addr; /* SysV shared memory for the header */
+ unsigned long seg_id; /* IPC key */
+} AnonymousMapping;
+
+static AnonymousMapping Mappings[ANON_MAPPINGS];
+
+/* Keeps track of used mapping segments */
+static int next_free_segment = 0;
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
@@ -104,6 +115,28 @@ static IpcMemoryState PGSharedMemoryAttach(IpcMemoryId shmId,
void *attachAt,
PGShmemHeader **addr);
+static const char*
+MappingName(int shmem_segment)
+{
+ switch (shmem_segment)
+ {
+ case MAIN_SHMEM_SEGMENT:
+ return "main";
+ default:
+ return "unknown";
+ }
+}
+
+static void
+DebugMappings()
+{
+ for(int i = 0; i < next_free_segment; i++)
+ {
+ AnonymousMapping m = Mappings[i];
+ elog(DEBUG1, "Mapping[%s]: addr %p, size %zu",
+ MappingName(i), m.shmem, m.shmem_size);
+ }
+}
/*
* InternalIpcMemoryCreate(memKey, size)
@@ -591,14 +624,13 @@ check_huge_page_size(int *newval, void **extra, GucSource source)
/*
* Creates an anonymous mmap()ed shared memory segment.
*
- * Pass the requested size in *size. This function will modify *size to the
- * actual size of the allocation, if it ends up allocating a segment that is
- * larger than requested.
+ * This function will modify mapping size to the actual size of the allocation,
+ * if it ends up allocating a segment that is larger than requested.
*/
-static void *
-CreateAnonymousSegment(Size *size)
+static void
+CreateAnonymousSegment(AnonymousMapping *mapping)
{
- Size allocsize = *size;
+ Size allocsize = mapping->shmem_size;
void *ptr = MAP_FAILED;
int mmap_errno = 0;
@@ -623,8 +655,11 @@ CreateAnonymousSegment(Size *size)
PG_MMAP_FLAGS | mmap_flags, -1, 0);
mmap_errno = errno;
if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
- elog(DEBUG1, "mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
- allocsize);
+ {
+ DebugMappings();
+ elog(DEBUG1, "segment[%s]: mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
+ MappingName(mapping->shmem_segment), allocsize);
+ }
}
#endif
@@ -642,7 +677,7 @@ CreateAnonymousSegment(Size *size)
* Use the original size, not the rounded-up value, when falling back
* to non-huge pages.
*/
- allocsize = *size;
+ allocsize = mapping->shmem_size;
ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
PG_MMAP_FLAGS, -1, 0);
mmap_errno = errno;
@@ -651,8 +686,10 @@ CreateAnonymousSegment(Size *size)
if (ptr == MAP_FAILED)
{
errno = mmap_errno;
+ DebugMappings();
ereport(FATAL,
- (errmsg("could not map anonymous shared memory: %m"),
+ (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment)),
(mmap_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request "
"for a shared memory segment exceeded available memory, "
@@ -663,8 +700,8 @@ CreateAnonymousSegment(Size *size)
allocsize) : 0));
}
- *size = allocsize;
- return ptr;
+ mapping->shmem = ptr;
+ mapping->shmem_size = allocsize;
}
/*
@@ -674,13 +711,18 @@ CreateAnonymousSegment(Size *size)
static void
AnonymousShmemDetach(int status, Datum arg)
{
- /* Release anonymous shared memory block, if any. */
- if (AnonymousShmem != NULL)
+ for(int i = 0; i < next_free_segment; i++)
{
- if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
- elog(LOG, "munmap(%p, %zu) failed: %m",
- AnonymousShmem, AnonymousShmemSize);
- AnonymousShmem = NULL;
+ AnonymousMapping m = Mappings[i];
+
+ /* Release anonymous shared memory block, if any. */
+ if (m.shmem != NULL)
+ {
+ if (munmap(m.shmem, m.shmem_size) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ m.shmem, m.shmem_size);
+ m.shmem = NULL;
+ }
}
}
@@ -705,6 +747,7 @@ PGSharedMemoryCreate(Size size,
PGShmemHeader *hdr;
struct stat statbuf;
Size sysvsize;
+ AnonymousMapping *mapping = &Mappings[next_free_segment];
/*
* We use the data directory's ID info (inode and device numbers) to
@@ -733,11 +776,15 @@ PGSharedMemoryCreate(Size size,
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+ mapping->shmem_size = size;
+ mapping->shmem_segment = next_free_segment;
if (shared_memory_type == SHMEM_TYPE_MMAP)
{
- AnonymousShmem = CreateAnonymousSegment(&size);
- AnonymousShmemSize = size;
+ /* On success, mapping data will be modified. */
+ CreateAnonymousSegment(mapping);
+
+ next_free_segment++;
/* Register on-exit routine to unmap the anonymous segment */
on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
@@ -760,7 +807,7 @@ PGSharedMemoryCreate(Size size,
* loop simultaneously. (CreateDataDirLockFile() does not entirely ensure
* that, but prefer fixing it over coping here.)
*/
- NextShmemSegID = statbuf.st_ino;
+ NextShmemSegID = statbuf.st_ino + next_free_segment;
for (;;)
{
@@ -852,13 +899,13 @@ PGSharedMemoryCreate(Size size,
/*
* Initialize space allocation status for segment.
*/
- hdr->totalsize = size;
+ hdr->totalsize = mapping->shmem_size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
*shim = hdr;
/* Save info for possible future use */
- UsedShmemSegAddr = memAddress;
- UsedShmemSegID = (unsigned long) NextShmemSegID;
+ mapping->seg_addr = memAddress;
+ mapping->seg_id = (unsigned long) NextShmemSegID;
/*
* If AnonymousShmem is NULL here, then we're not using anonymous shared
@@ -866,10 +913,10 @@ PGSharedMemoryCreate(Size size,
* block. Otherwise, the System V shared memory block is only a shim, and
* we must return a pointer to the real block.
*/
- if (AnonymousShmem == NULL)
+ if (mapping->shmem == NULL)
return hdr;
- memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
- return (PGShmemHeader *) AnonymousShmem;
+ memcpy(mapping->shmem, hdr, sizeof(PGShmemHeader));
+ return (PGShmemHeader *) mapping->shmem;
}
#ifdef EXEC_BACKEND
@@ -969,23 +1016,28 @@ PGSharedMemoryNoReAttach(void)
void
PGSharedMemoryDetach(void)
{
- if (UsedShmemSegAddr != NULL)
+ for(int i = 0; i < next_free_segment; i++)
{
- if ((shmdt(UsedShmemSegAddr) < 0)
+ AnonymousMapping m = Mappings[i];
+
+ if (m.seg_addr != NULL)
+ {
+ if ((shmdt(m.seg_addr) < 0)
#if defined(EXEC_BACKEND) && defined(__CYGWIN__)
- /* Work-around for cygipc exec bug */
- && shmdt(NULL) < 0
+ /* Work-around for cygipc exec bug */
+ && shmdt(NULL) < 0
#endif
- )
- elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
- UsedShmemSegAddr = NULL;
- }
+ )
+ elog(LOG, "shmdt(%p) failed: %m", m.seg_addr);
+ m.seg_addr = NULL;
+ }
- if (AnonymousShmem != NULL)
- {
- if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
- elog(LOG, "munmap(%p, %zu) failed: %m",
- AnonymousShmem, AnonymousShmemSize);
- AnonymousShmem = NULL;
+ if (m.shmem != NULL)
+ {
+ if (munmap(m.shmem, m.shmem_size) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ m.shmem, m.shmem_size);
+ m.shmem = NULL;
+ }
}
}
diff --git a/src/backend/port/win32_sema.c b/src/backend/port/win32_sema.c
index 5854ad1f54d..e7365ff8060 100644
--- a/src/backend/port/win32_sema.c
+++ b/src/backend/port/win32_sema.c
@@ -44,7 +44,7 @@ PGSemaphoreShmemSize(int maxSemas)
* process exits.
*/
void
-PGReserveSemaphores(int maxSemas)
+PGReserveSemaphores(int maxSemas, int shmem_segment)
{
mySemSet = (HANDLE *) malloc(maxSemas * sizeof(HANDLE));
if (mySemSet == NULL)
diff --git a/src/backend/storage/ipc/ipc.c b/src/backend/storage/ipc/ipc.c
index 567739b5be9..5b55bec8d9d 100644
--- a/src/backend/storage/ipc/ipc.c
+++ b/src/backend/storage/ipc/ipc.c
@@ -61,6 +61,8 @@ static void proc_exit_prepare(int code);
* but provide some additional features we need --- in particular,
* we want to register callbacks to invoke when we are disconnecting
* from a broken shared-memory context but not exiting the postmaster.
+ * Maximum number of such exit callbacks depends on the number of shared
+ * segments.
*
* Callback functions can take zero, one, or two args: the first passed
* arg is the integer exitcode, the second is the Datum supplied when
@@ -68,7 +70,7 @@ static void proc_exit_prepare(int code);
* ----------------------------------------------------------------
*/
-#define MAX_ON_EXITS 20
+#define MAX_ON_EXITS 40
struct ONEXIT
{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2fa045e6b0f..8b38e985327 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -86,7 +86,7 @@ RequestAddinShmemSpace(Size size)
* required.
*/
Size
-CalculateShmemSize(int *num_semaphores)
+CalculateShmemSize(int *num_semaphores, int shmem_segment)
{
Size size;
int numSemas;
@@ -206,33 +206,38 @@ CreateSharedMemoryAndSemaphores(void)
Assert(!IsUnderPostmaster);
- /* Compute the size of the shared-memory block */
- size = CalculateShmemSize(&numSemas);
- elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
-
- /*
- * Create the shmem segment
- */
- seghdr = PGSharedMemoryCreate(size, &shim);
-
- /*
- * Make sure that huge pages are never reported as "unknown" while the
- * server is running.
- */
- Assert(strcmp("unknown",
- GetConfigOption("huge_pages_status", false, false)) != 0);
-
- InitShmemAccess(seghdr);
-
- /*
- * Create semaphores
- */
- PGReserveSemaphores(numSemas);
-
- /*
- * Set up shared memory allocation mechanism
- */
- InitShmemAllocation();
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ /* Compute the size of the shared-memory block */
+ size = CalculateShmemSize(&numSemas, segment);
+ elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
+
+ /*
+ * Create the shmem segment.
+ *
+ * XXX: Do multiple shims are needed, one per segment?
+ */
+ seghdr = PGSharedMemoryCreate(size, &shim);
+
+ /*
+ * Make sure that huge pages are never reported as "unknown" while the
+ * server is running.
+ */
+ Assert(strcmp("unknown",
+ GetConfigOption("huge_pages_status", false, false)) != 0);
+
+ InitShmemAccessInSegment(seghdr, segment);
+
+ /*
+ * Create semaphores
+ */
+ PGReserveSemaphores(numSemas, segment);
+
+ /*
+ * Set up shared memory allocation mechanism
+ */
+ InitShmemAllocationInSegment(segment);
+ }
/* Initialize subsystems */
CreateOrAttachShmemStructs();
@@ -363,7 +368,7 @@ InitializeShmemGUCs(void)
/*
* Calculate the shared memory size and round up to the nearest megabyte.
*/
- size_b = CalculateShmemSize(&num_semas);
+ size_b = CalculateShmemSize(&num_semas, MAIN_SHMEM_SEGMENT);
size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
sprintf(buf, "%zu", size_mb);
SetConfigOption("shared_memory_size", buf,
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index c9ae3b45b76..72255a1c5ca 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -76,19 +76,19 @@
#include "utils/builtins.h"
static void *ShmemAllocRaw(Size size, Size *allocated_size);
+static void *ShmemAllocRawInSegment(Size size, Size *allocated_size,
+ int shmem_segment);
/* shared memory global variables */
-static PGShmemHeader *ShmemSegHdr; /* shared mem segment header */
+ShmemSegment Segments[ANON_MAPPINGS];
-static void *ShmemBase; /* start address of shared memory */
-
-static void *ShmemEnd; /* end+1 address of shared memory */
-
-slock_t *ShmemLock; /* spinlock for shared memory and LWLock
- * allocation */
-
-static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */
+/*
+ * Primary index hashtable for shmem, for simplicity we use a single for all
+ * shared memory segments. There can be performance consequences of that, and
+ * an alternative option would be to have one index per shared memory segments.
+ */
+static HTAB *ShmemIndex = NULL;
/* To get reliable results for NUMA inquiry we need to "touch pages" once */
static bool firstNumaTouch = true;
@@ -101,9 +101,17 @@ Datum pg_numa_available(PG_FUNCTION_ARGS);
void
InitShmemAccess(PGShmemHeader *seghdr)
{
- ShmemSegHdr = seghdr;
- ShmemBase = seghdr;
- ShmemEnd = (char *) ShmemBase + seghdr->totalsize;
+ InitShmemAccessInSegment(seghdr, MAIN_SHMEM_SEGMENT);
+}
+
+void
+InitShmemAccessInSegment(PGShmemHeader *seghdr, int shmem_segment)
+{
+ PGShmemHeader *shmhdr = (PGShmemHeader *) seghdr;
+ ShmemSegment *seg = &Segments[shmem_segment];
+ seg->ShmemSegHdr = shmhdr;
+ seg->ShmemBase = (void *) shmhdr;
+ seg->ShmemEnd = (char *) seg->ShmemBase + shmhdr->totalsize;
}
/*
@@ -114,7 +122,13 @@ InitShmemAccess(PGShmemHeader *seghdr)
void
InitShmemAllocation(void)
{
- PGShmemHeader *shmhdr = ShmemSegHdr;
+ InitShmemAllocationInSegment(MAIN_SHMEM_SEGMENT);
+}
+
+void
+InitShmemAllocationInSegment(int shmem_segment)
+{
+ PGShmemHeader *shmhdr = Segments[shmem_segment].ShmemSegHdr;
char *aligned;
Assert(shmhdr != NULL);
@@ -123,9 +137,9 @@ InitShmemAllocation(void)
* Initialize the spinlock used by ShmemAlloc. We must use
* ShmemAllocUnlocked, since obviously ShmemAlloc can't be called yet.
*/
- ShmemLock = (slock_t *) ShmemAllocUnlocked(sizeof(slock_t));
+ Segments[shmem_segment].ShmemLock = (slock_t *) ShmemAllocUnlockedInSegment(sizeof(slock_t), shmem_segment);
- SpinLockInit(ShmemLock);
+ SpinLockInit(Segments[shmem_segment].ShmemLock);
/*
* Allocations after this point should go through ShmemAlloc, which
@@ -150,11 +164,17 @@ InitShmemAllocation(void)
*/
void *
ShmemAlloc(Size size)
+{
+ return ShmemAllocInSegment(size, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemAllocInSegment(Size size, int shmem_segment)
{
void *newSpace;
Size allocated_size;
- newSpace = ShmemAllocRaw(size, &allocated_size);
+ newSpace = ShmemAllocRawInSegment(size, &allocated_size, shmem_segment);
if (!newSpace)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -184,6 +204,12 @@ ShmemAllocNoError(Size size)
*/
static void *
ShmemAllocRaw(Size size, Size *allocated_size)
+{
+ return ShmemAllocRawInSegment(size, allocated_size, MAIN_SHMEM_SEGMENT);
+}
+
+static void *
+ShmemAllocRawInSegment(Size size, Size *allocated_size, int shmem_segment)
{
Size newStart;
Size newFree;
@@ -203,22 +229,22 @@ ShmemAllocRaw(Size size, Size *allocated_size)
size = CACHELINEALIGN(size);
*allocated_size = size;
- Assert(ShmemSegHdr != NULL);
+ Assert(Segments[shmem_segment].ShmemSegHdr != NULL);
- SpinLockAcquire(ShmemLock);
+ SpinLockAcquire(Segments[shmem_segment].ShmemLock);
- newStart = ShmemSegHdr->freeoffset;
+ newStart = Segments[shmem_segment].ShmemSegHdr->freeoffset;
newFree = newStart + size;
- if (newFree <= ShmemSegHdr->totalsize)
+ if (newFree <= Segments[shmem_segment].ShmemSegHdr->totalsize)
{
- newSpace = (char *) ShmemBase + newStart;
- ShmemSegHdr->freeoffset = newFree;
+ newSpace = (char *) Segments[shmem_segment].ShmemBase + newStart;
+ Segments[shmem_segment].ShmemSegHdr->freeoffset = newFree;
}
else
newSpace = NULL;
- SpinLockRelease(ShmemLock);
+ SpinLockRelease(Segments[shmem_segment].ShmemLock);
/* note this assert is okay with newSpace == NULL */
Assert(newSpace == (void *) CACHELINEALIGN(newSpace));
@@ -236,6 +262,12 @@ ShmemAllocRaw(Size size, Size *allocated_size)
*/
void *
ShmemAllocUnlocked(Size size)
+{
+ return ShmemAllocUnlockedInSegment(size, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemAllocUnlockedInSegment(Size size, int shmem_segment)
{
Size newStart;
Size newFree;
@@ -246,19 +278,19 @@ ShmemAllocUnlocked(Size size)
*/
size = MAXALIGN(size);
- Assert(ShmemSegHdr != NULL);
+ Assert(Segments[shmem_segment].ShmemSegHdr != NULL);
- newStart = ShmemSegHdr->freeoffset;
+ newStart = Segments[shmem_segment].ShmemSegHdr->freeoffset;
newFree = newStart + size;
- if (newFree > ShmemSegHdr->totalsize)
+ if (newFree > Segments[shmem_segment].ShmemSegHdr->totalsize)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of shared memory (%zu bytes requested)",
size)));
- ShmemSegHdr->freeoffset = newFree;
+ Segments[shmem_segment].ShmemSegHdr->freeoffset = newFree;
- newSpace = (char *) ShmemBase + newStart;
+ newSpace = (char *) Segments[shmem_segment].ShmemBase + newStart;
Assert(newSpace == (void *) MAXALIGN(newSpace));
@@ -273,7 +305,13 @@ ShmemAllocUnlocked(Size size)
bool
ShmemAddrIsValid(const void *addr)
{
- return (addr >= ShmemBase) && (addr < ShmemEnd);
+ return ShmemAddrIsValidInSegment(addr, MAIN_SHMEM_SEGMENT);
+}
+
+bool
+ShmemAddrIsValidInSegment(const void *addr, int shmem_segment)
+{
+ return (addr >= Segments[shmem_segment].ShmemBase) && (addr < Segments[shmem_segment].ShmemEnd);
}
/*
@@ -334,6 +372,18 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
long max_size, /* max size of the table */
HASHCTL *infoP, /* info about key and bucket size */
int hash_flags) /* info about infoP */
+{
+ return ShmemInitHashInSegment(name, init_size, max_size, infoP, hash_flags,
+ MAIN_SHMEM_SEGMENT);
+}
+
+HTAB *
+ShmemInitHashInSegment(const char *name, /* table string name for shmem index */
+ long init_size, /* initial table size */
+ long max_size, /* max size of the table */
+ HASHCTL *infoP, /* info about key and bucket size */
+ int hash_flags, /* info about infoP */
+ int shmem_segment) /* in which segment to keep the table */
{
bool found;
void *location;
@@ -350,9 +400,9 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE;
/* look it up in the shmem index */
- location = ShmemInitStruct(name,
+ location = ShmemInitStructInSegment(name,
hash_get_shared_size(infoP, hash_flags),
- &found);
+ &found, shmem_segment);
/*
* if it already exists, attach to it rather than allocate and initialize
@@ -385,6 +435,13 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
*/
void *
ShmemInitStruct(const char *name, Size size, bool *foundPtr)
+{
+ return ShmemInitStructInSegment(name, size, foundPtr, MAIN_SHMEM_SEGMENT);
+}
+
+void *
+ShmemInitStructInSegment(const char *name, Size size, bool *foundPtr,
+ int shmem_segment)
{
ShmemIndexEnt *result;
void *structPtr;
@@ -393,7 +450,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
if (!ShmemIndex)
{
- PGShmemHeader *shmemseghdr = ShmemSegHdr;
+ PGShmemHeader *shmemseghdr = Segments[shmem_segment].ShmemSegHdr;
/* Must be trying to create/attach to ShmemIndex itself */
Assert(strcmp(name, "ShmemIndex") == 0);
@@ -416,7 +473,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
* process can be accessing shared memory yet.
*/
Assert(shmemseghdr->index == NULL);
- structPtr = ShmemAlloc(size);
+ structPtr = ShmemAllocInSegment(size, shmem_segment);
shmemseghdr->index = structPtr;
*foundPtr = false;
}
@@ -433,8 +490,8 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
LWLockRelease(ShmemIndexLock);
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("could not create ShmemIndex entry for data structure \"%s\"",
- name)));
+ errmsg("could not create ShmemIndex entry for data structure \"%s\" in segment %d",
+ name, shmem_segment)));
}
if (*foundPtr)
@@ -459,7 +516,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
Size allocated_size;
/* It isn't in the table yet. allocate and initialize it */
- structPtr = ShmemAllocRaw(size, &allocated_size);
+ structPtr = ShmemAllocRawInSegment(size, &allocated_size, shmem_segment);
if (structPtr == NULL)
{
/* out of memory; remove the failed ShmemIndex entry */
@@ -478,14 +535,13 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
LWLockRelease(ShmemIndexLock);
- Assert(ShmemAddrIsValid(structPtr));
+ Assert(ShmemAddrIsValidInSegment(structPtr, shmem_segment));
Assert(structPtr == (void *) CACHELINEALIGN(structPtr));
return structPtr;
}
-
/*
* Add two Size values, checking for overflow
*/
@@ -542,10 +598,11 @@ pg_get_shmem_allocations(PG_FUNCTION_ARGS)
/* output all allocated entries */
memset(nulls, 0, sizeof(nulls));
+ /* XXX: take all shared memory segments into account. */
while ((ent = (ShmemIndexEnt *) hash_seq_search(&hstat)) != NULL)
{
values[0] = CStringGetTextDatum(ent->key);
- values[1] = Int64GetDatum((char *) ent->location - (char *) ShmemSegHdr);
+ values[1] = Int64GetDatum((char *) ent->location - (char *) Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr);
values[2] = Int64GetDatum(ent->size);
values[3] = Int64GetDatum(ent->allocated_size);
named_allocated += ent->allocated_size;
@@ -557,15 +614,15 @@ pg_get_shmem_allocations(PG_FUNCTION_ARGS)
/* output shared memory allocated but not counted via the shmem index */
values[0] = CStringGetTextDatum("<anonymous>");
nulls[1] = true;
- values[2] = Int64GetDatum(ShmemSegHdr->freeoffset - named_allocated);
+ values[2] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset - named_allocated);
values[3] = values[2];
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
/* output as-of-yet unused shared memory */
nulls[0] = true;
- values[1] = Int64GetDatum(ShmemSegHdr->freeoffset);
+ values[1] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset);
nulls[1] = false;
- values[2] = Int64GetDatum(ShmemSegHdr->totalsize - ShmemSegHdr->freeoffset);
+ values[2] = Int64GetDatum(Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->totalsize - Segments[MAIN_SHMEM_SEGMENT].ShmemSegHdr->freeoffset);
values[3] = values[2];
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
@@ -630,7 +687,12 @@ pg_get_shmem_allocations_numa(PG_FUNCTION_ARGS)
* this is not very likely, and moreover we have more entries, each of
* them using only fraction of the total pages.
*/
- shm_total_page_count = (ShmemSegHdr->totalsize / os_page_size) + 1;
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ PGShmemHeader *shmhdr = Segments[segment].ShmemSegHdr;
+ shm_total_page_count += (shmhdr->totalsize / os_page_size) + 1;
+ }
+
page_ptrs = palloc0(sizeof(void *) * shm_total_page_count);
pages_status = palloc(sizeof(int) * shm_total_page_count);
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 46f44bc4511..a36b08895c8 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -80,6 +80,8 @@
#include "pg_trace.h"
#include "pgstat.h"
#include "port/pg_bitutils.h"
+#include "postmaster/postmaster.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/proclist.h"
#include "storage/procnumber.h"
@@ -618,10 +620,15 @@ LWLockNewTrancheId(void)
int *LWLockCounter;
LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
- /* We use the ShmemLock spinlock to protect LWLockCounter */
- SpinLockAcquire(ShmemLock);
+ /*
+ * We use the ShmemLock spinlock to protect LWLockCounter.
+ *
+ * XXX: Looks like this is the only use of Segments outside of shmem.c,
+ * it's maybe worth it to reshape this part to hide Segments structure.
+ */
+ SpinLockAcquire(Segments[MAIN_SHMEM_SEGMENT].ShmemLock);
result = (*LWLockCounter)++;
- SpinLockRelease(ShmemLock);
+ SpinLockRelease(Segments[MAIN_SHMEM_SEGMENT].ShmemLock);
return result;
}
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 3baf418b3d1..6ebda479ced 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -77,7 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
/* ipci.c */
extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
-extern Size CalculateShmemSize(int *num_semaphores);
+extern Size CalculateShmemSize(int *num_semaphores, int shmem_segment);
extern void CreateSharedMemoryAndSemaphores(void);
#ifdef EXEC_BACKEND
extern void AttachSharedMemoryStructs(void);
diff --git a/src/include/storage/pg_sema.h b/src/include/storage/pg_sema.h
index fa6ca35a51f..8ae9637fcd0 100644
--- a/src/include/storage/pg_sema.h
+++ b/src/include/storage/pg_sema.h
@@ -41,7 +41,7 @@ typedef HANDLE PGSemaphore;
extern Size PGSemaphoreShmemSize(int maxSemas);
/* Module initialization (called during postmaster start or shmem reinit) */
-extern void PGReserveSemaphores(int maxSemas);
+extern void PGReserveSemaphores(int maxSemas, int shmem_segment);
/* Allocate a PGSemaphore structure with initial count 1 */
extern PGSemaphore PGSemaphoreCreate(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 5f7d4b83a60..2348c59b5a0 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -25,6 +25,7 @@
#define PG_SHMEM_H
#include "storage/dsm_impl.h"
+#include "storage/spin.h"
typedef struct PGShmemHeader /* standard header for all Postgres shmem */
{
@@ -41,6 +42,20 @@ typedef struct PGShmemHeader /* standard header for all Postgres shmem */
#endif
} PGShmemHeader;
+typedef struct ShmemSegment
+{
+ PGShmemHeader *ShmemSegHdr; /* shared mem segment header */
+ void *ShmemBase; /* start address of shared memory */
+ void *ShmemEnd; /* end+1 address of shared memory */
+ slock_t *ShmemLock; /* spinlock for shared memory and LWLock
+ * allocation */
+} ShmemSegment;
+
+/* Number of available segments for anonymous memory mappings */
+#define ANON_MAPPINGS 1
+
+extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
+
/* GUC variables */
extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
@@ -91,4 +106,7 @@ extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
+/* The main segment, contains everything except buffer blocks and related data. */
+#define MAIN_SHMEM_SEGMENT 0
+
#endif /* PG_SHMEM_H */
diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h
index c1f668ded95..69663d412c3 100644
--- a/src/include/storage/shmem.h
+++ b/src/include/storage/shmem.h
@@ -29,15 +29,27 @@
extern PGDLLIMPORT slock_t *ShmemLock;
struct PGShmemHeader; /* avoid including storage/pg_shmem.h here */
extern void InitShmemAccess(struct PGShmemHeader *seghdr);
+extern void InitShmemAccessInSegment(struct PGShmemHeader *seghdr,
+ int shmem_segment);
extern void InitShmemAllocation(void);
+extern void InitShmemAllocationInSegment(int shmem_segment);
extern void *ShmemAlloc(Size size);
+extern void *ShmemAllocInSegment(Size size, int shmem_segment);
extern void *ShmemAllocNoError(Size size);
extern void *ShmemAllocUnlocked(Size size);
+extern void *ShmemAllocUnlockedInSegment(Size size, int shmem_segment);
extern bool ShmemAddrIsValid(const void *addr);
+extern bool ShmemAddrIsValidInSegment(const void *addr, int shmem_segment);
extern void InitShmemIndex(void);
+extern void InitVariableShmemIndex(void);
extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size,
HASHCTL *infoP, int hash_flags);
+extern HTAB *ShmemInitHashInSegment(const char *name, long init_size,
+ long max_size, HASHCTL *infoP,
+ int hash_flags, int shmem_segment);
extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
+extern void *ShmemInitStructInSegment(const char *name, Size size,
+ bool *foundPtr, int shmem_segment);
extern Size add_size(Size s1, Size s2);
extern Size mul_size(Size s1, Size s2);
--
2.49.0
[text/plain] v5-0005-Address-space-reservation-for-shared-memory.patch (24.2K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/6-v5-0005-Address-space-reservation-for-shared-memory.patch)
download | inline diff:
From 6238657ddb8c9e63d28a1a96712278f548d3292c Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 11:47:04 +0200
Subject: [PATCH v5 05/10] Address space reservation for shared memory
Currently the shared memory layout is designed to pack everything tight
together, leaving no space between mappings for resizing. Here is how it
looks like for one mapping in /proc/$PID/maps, /dev/zero represents the
anonymous shared memory we talk about:
00400000-00490000 /path/bin/postgres
...
012d9000-0133e000 [heap]
7f443a800000-7f470a800000 /dev/zero (deleted)
7f470a800000-7f471831d000 /usr/lib/locale/locale-archive
7f4718400000-7f4718401000 /usr/lib64/libstdc++.so.6.0.34
...
Make the layout more dynamic via splitting every shared memory segment
into two parts:
* An anonymous file, which actually contains shared memory content. Such
an anonymous file is created via memfd_create, it lives in memory,
behaves like a regular file and semantically equivalent to an
anonymous memory allocated via mmap with MAP_ANONYMOUS.
* A reservation mapping, which size is much larger than required shared
segment size. This mapping is created with flags PROT_NONE (which
makes sure the reserved space is not used), and MAP_NORESERVE (to not
count the reserved space against memory limits). The anonymous file is
mapped into this reservation mapping.
The resulting layout looks like this:
00400000-00490000 /path/bin/postgres
...
3f526000-3f590000 rw-p [heap]
7fbd827fe000-7fbd8bdde000 rw-s /memfd:main (deleted) -- anon file
7fbd8bdde000-7fbe82800000 ---s /memfd:main (deleted) -- reservation
7fbe82800000-7fbe90670000 r--p /usr/lib/locale/locale-archive
7fbe90800000-7fbe90941000 r-xp /usr/lib64/libstdc++.so.6.0.34
To resize a shared memory segment in this layout it's possible to use ftruncate
on the anonymous file, adjusting access permissions on the reserved space as
needed.
This approach also do not impact the actual memory usage as reported by
the kernel. Here is the output of /proc/$PID/status for the master
version with shared_buffers = 128 MB:
// Peak virtual memory size, which is described as total pages
// mapped in mm_struct. It corresponds to the mapped reserved space
// and is the only number that grows with it.
VmPeak: 2043192 kB
// Size of memory portions. It contains RssAnon + RssFile + RssShmem
VmRSS: 22908 kB
// Size of resident anonymous memory
RssAnon: 768 kB
// Size of resident file mappings
RssFile: 10364 kB
// Size of resident shmem memory (includes SysV shm, mapping of tmpfs and
// shared anonymous mappings)
RssShmem: 11776 kB
Here is the same for the patch when reserving 20GB of space:
VmPeak: 21255824 kB
VmRSS: 25020 kB
RssAnon: 768 kB
RssFile: 10812 kB
RssShmem: 13440 kB
Cgroup v2 doesn't have any problems with that as well. To verify a new cgroup
was created with the memory limit 256 MB, then PostgreSQL was launched withing
this cgroup with shared_buffers = 128 MB:
$ cd /sys/fs/cgroup
$ mkdir postgres
$ cd postres
$ echo 268435456 > memory.max
$ echo $MASTER_PID_SHELL > cgroup.procs
# postgres from the master branch has being successfully launched
# from that shell
$ cat memory.current
17465344 (~16.6 MB)
# stop postgres
$ echo $PATCH_PID_SHELL > cgroup.procs
# postgres from the patch has being successfully launched from that shell
$ cat memory.current
20770816 (~19.8 MB)
To control the amount of space reserved a new GUC max_available_memory
is introduced. Ideally it should be based on the maximum available
memory, hense the name.
There are also few unrelated advantages of using anon files:
* We've got a file descriptor, which could be used for regular file
operations (modification, truncation, you name it).
* The file could be given a name, which improves readability when it
comes to process maps.
* By default, Linux will not add file-backed shared mappings into a core dump,
making it more convenient to work with them in PostgreSQL: no more huge dumps
to process.
The downside is that memfd_create is Linux specific.
---
src/backend/port/sysv_shmem.c | 290 ++++++++++++++++++++++------
src/backend/port/win32_shmem.c | 2 +-
src/backend/storage/ipc/ipci.c | 5 +-
src/backend/storage/ipc/shmem.c | 2 +-
src/backend/utils/init/globals.c | 1 +
src/backend/utils/misc/guc_tables.c | 14 ++
src/include/miscadmin.h | 1 +
src/include/portability/mem.h | 2 +-
src/include/storage/pg_shmem.h | 5 +-
9 files changed, 262 insertions(+), 60 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 56af0231d24..363ddfd1fca 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -97,10 +97,12 @@ void *UsedShmemSegAddr = NULL;
typedef struct AnonymousMapping
{
int shmem_segment;
- Size shmem_size; /* Size of the mapping */
+ Size shmem_size; /* Size of the actually used memory */
+ Size shmem_reserved; /* Size of the reserved mapping */
Pointer shmem; /* Pointer to the start of the mapped memory */
Pointer seg_addr; /* SysV shared memory for the header */
unsigned long seg_id; /* IPC key */
+ int segment_fd; /* fd for the backing anon file */
} AnonymousMapping;
static AnonymousMapping Mappings[ANON_MAPPINGS];
@@ -108,6 +110,49 @@ static AnonymousMapping Mappings[ANON_MAPPINGS];
/* Keeps track of used mapping segments */
static int next_free_segment = 0;
+/*
+ * Anonymous mapping layout we use looks like this:
+ *
+ * 00400000-00c2a000 r-xp /bin/postgres
+ * ...
+ * 3f526000-3f590000 rw-p [heap]
+ * 7fbd827fe000-7fbd8bdde000 rw-s /memfd:main (deleted)
+ * 7fbd8bdde000-7fbe82800000 ---s /memfd:main (deleted)
+ * 7fbe82800000-7fbe90670000 r--p /usr/lib/locale/locale-archive
+ * 7fbe90800000-7fbe90941000 r-xp /usr/lib64/libstdc++.so.6.0.34
+ * ...
+ *
+ * We need to place shared memory mappings in such a way, that there will be
+ * gaps between them in the address space. Those gaps have to be large enough
+ * to resize the mapping up to certain size, without counting towards the total
+ * memory consumption.
+ *
+ * To achieve this, for each shared memory segment we first create an anonymous
+ * file of specified size using memfd_create, which will accomodate actual
+ * shared memory mapping content. It is represented by the first /memfd:main
+ * with rw permissions. Then we create a mapping for this file using mmap, with
+ * size much larger than required and flags PROT_NONE (allows to make sure the
+ * reserved space will not be used) and MAP_NORESERVE (prevents the space from
+ * being counted against memory limits). The mapping serves as an address space
+ * reservation, into which shared memory segment can be extended and is
+ * represented by the second /memfd:main with no permissions.
+ *
+ * The reserved space for each segment is calculated as a fraction of the total
+ * reserved space (MaxAvailableMemory), as specified in the SHMEM_RESIZE_RATIO
+ * array.
+ */
+static double SHMEM_RESIZE_RATIO[1] = {
+ 1.0, /* MAIN_SHMEM_SLOT */
+};
+
+/*
+ * Flag telling that we have decided to use huge pages.
+ *
+ * XXX: It's possible to use GetConfigOption("huge_pages_status", false, false)
+ * instead, but it feels like an overkill.
+ */
+static bool huge_pages_on = false;
+
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
@@ -503,19 +548,20 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
* hugepage sizes, we might want to think about more invasive strategies,
* such as increasing shared_buffers to absorb the extra space.
*
- * Returns the (real, assumed or config provided) page size into
- * *hugepagesize, and the hugepage-related mmap flags to use into
- * *mmap_flags if requested by the caller. If huge pages are not supported,
- * *hugepagesize and *mmap_flags are set to 0.
+ * Returns the (real, assumed or config provided) page size into *hugepagesize,
+ * the hugepage-related mmap and memfd flags to use into *mmap_flags and
+ * *memfd_flags if requested by the caller. If huge pages are not supported,
+ * *hugepagesize, *mmap_flags and *memfd_flags are set to 0.
*/
void
-GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+GetHugePageSize(Size *hugepagesize, int *mmap_flags, int *memfd_flags)
{
#ifdef MAP_HUGETLB
Size default_hugepagesize = 0;
Size hugepagesize_local = 0;
int mmap_flags_local = 0;
+ int memfd_flags_local = 0;
/*
* System-dependent code to find out the default huge page size.
@@ -574,6 +620,7 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
}
mmap_flags_local = MAP_HUGETLB;
+ memfd_flags_local = MFD_HUGETLB;
/*
* On recent enough Linux, also include the explicit page size, if
@@ -584,7 +631,16 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
{
int shift = pg_ceil_log2_64(hugepagesize_local);
- mmap_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
+ memfd_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
+ }
+#endif
+
+#if defined(MFD_HUGE_MASK) && defined(MFD_HUGE_SHIFT)
+ if (hugepagesize_local != default_hugepagesize)
+ {
+ int shift = pg_ceil_log2_64(hugepagesize_local);
+
+ memfd_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
}
#endif
@@ -593,6 +649,8 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
*mmap_flags = mmap_flags_local;
if (hugepagesize)
*hugepagesize = hugepagesize_local;
+ if (memfd_flags)
+ *memfd_flags = memfd_flags_local;
#else
@@ -600,6 +658,8 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
*hugepagesize = 0;
if (mmap_flags)
*mmap_flags = 0;
+ if (memfd_flags)
+ *memfd_flags = 0;
#endif /* MAP_HUGETLB */
}
@@ -625,72 +685,90 @@ check_huge_page_size(int *newval, void **extra, GucSource source)
* Creates an anonymous mmap()ed shared memory segment.
*
* This function will modify mapping size to the actual size of the allocation,
- * if it ends up allocating a segment that is larger than requested.
+ * if it ends up allocating a segment that is larger than requested. If needed,
+ * it also rounds up the mapping reserved size to be a multiple of huge page
+ * size.
+ *
+ * Note that we do not fallback from huge pages to regular pages in this
+ * function, this decision was already made in ReserveAnonymousMemory and we
+ * stick to it.
*/
static void
CreateAnonymousSegment(AnonymousMapping *mapping)
{
Size allocsize = mapping->shmem_size;
void *ptr = MAP_FAILED;
- int mmap_errno = 0;
+ int save_errno = 0;
+ int mmap_flags = PG_MMAP_FLAGS, memfd_flags = 0;
+
+ elog(DEBUG1, "segment[%s]: size %zu, reserved %zu",
+ MappingName(mapping->shmem_segment), mapping->shmem_size,
+ mapping->shmem_reserved);
#ifndef MAP_HUGETLB
- /* PGSharedMemoryCreate should have dealt with this case */
- Assert(huge_pages != HUGE_PAGES_ON);
+ /* PrepareHugePages should have dealt with this case */
+ Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
#else
- if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ if (huge_pages_on)
{
- /*
- * Round up the request size to a suitable large value.
- */
Size hugepagesize;
- int mmap_flags;
- GetHugePageSize(&hugepagesize, &mmap_flags);
+ /* Make sure nothing is messed up */
+ Assert(huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY);
+
+ /* Round up the request size to a suitable large value */
+ GetHugePageSize(&hugepagesize, &mmap_flags, &memfd_flags);
if (allocsize % hugepagesize != 0)
allocsize += hugepagesize - (allocsize % hugepagesize);
- ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
- PG_MMAP_FLAGS | mmap_flags, -1, 0);
- mmap_errno = errno;
- if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
- {
- DebugMappings();
- elog(DEBUG1, "segment[%s]: mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
- MappingName(mapping->shmem_segment), allocsize);
- }
+ /*
+ * The reserved space is multiple of BLCKSZ. We know the huge page
+ * size, round up the reserved space to it.
+ */
+ mapping->shmem_reserved = mapping->shmem_reserved + hugepagesize -
+ (mapping->shmem_reserved % hugepagesize);
+
+ /* Verify that the new size is withing the reserved boundaries */
+ if (mapping->shmem_reserved < mapping->shmem_size)
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+ errmsg("not enough shared memory is reserved"),
+ errhint("You may need to increase \"max_available_memory\".")));
+
+ mmap_flags = PG_MMAP_FLAGS | mmap_flags;
}
#endif
/*
- * Report whether huge pages are in use. This needs to be tracked before
- * the second mmap() call if attempting to use huge pages failed
- * previously.
+ * Prepare an anonymous file backing the segment. Its size will be
+ * specified later via ftruncate.
+ *
+ * The file behaves like a regular file, but lives in memory. Once all
+ * references to the file are dropped, it is automatically released.
+ * Anonymous memory is used for all backing pages of the file, thus it has
+ * the same semantics as anonymous memory allocations using mmap with the
+ * MAP_ANONYMOUS flag.
*/
- SetConfigOption("huge_pages_status", (ptr == MAP_FAILED) ? "off" : "on",
- PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+ mapping->segment_fd = memfd_create(MappingName(mapping->shmem_segment),
+ memfd_flags);
- if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
+ /*
+ * Specify the segment file size using allocsize, which contains
+ * potentially modified value.
+ */
+ if(ftruncate(mapping->segment_fd, allocsize) == -1)
{
- /*
- * Use the original size, not the rounded-up value, when falling back
- * to non-huge pages.
- */
- allocsize = mapping->shmem_size;
- ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
- PG_MMAP_FLAGS, -1, 0);
- mmap_errno = errno;
- }
+ save_errno = errno;
- if (ptr == MAP_FAILED)
- {
- errno = mmap_errno;
DebugMappings();
+ close(mapping->segment_fd);
+
+ errno = save_errno;
ereport(FATAL,
- (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ (errmsg("segment[%s]: could not truncate anonymous file: %m",
MappingName(mapping->shmem_segment)),
- (mmap_errno == ENOMEM) ?
+ (save_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request "
"for a shared memory segment exceeded available memory, "
"swap space, or huge pages. To reduce the request size "
@@ -700,10 +778,112 @@ CreateAnonymousSegment(AnonymousMapping *mapping)
allocsize) : 0));
}
+ elog(DEBUG1, "segment[%s]: mmap(%zu)",
+ MappingName(mapping->shmem_segment), allocsize);
+
+ /*
+ * Create a reservation mapping.
+ */
+ ptr = mmap(NULL, mapping->shmem_reserved, PROT_NONE,
+ mmap_flags | MAP_NORESERVE, mapping->segment_fd, 0);
+ save_errno = errno;
+
+ if (ptr == MAP_FAILED)
+ {
+ DebugMappings();
+
+ errno = save_errno;
+ ereport(FATAL,
+ (errmsg("segment[%s]: could not map anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment))));
+ }
+
+ /* Make the memory accessible */
+ if(mprotect(ptr, allocsize, PROT_READ | PROT_WRITE) == -1)
+ {
+ save_errno = errno;
+ DebugMappings();
+
+ errno = save_errno;
+ ereport(FATAL,
+ (errmsg("segment[%s]: could not mprotect anonymous shared memory: %m",
+ MappingName(mapping->shmem_segment))));
+ }
+
mapping->shmem = ptr;
mapping->shmem_size = allocsize;
}
+/*
+ * PrepareHugePages
+ *
+ * Figure out if there are enough huge pages to allocate all shared memory
+ * segments, and report that information via huge_pages_status and
+ * huge_pages_on. It needs to be called before creating shared memory segments.
+ *
+ * It is necessary to maintain the same semantic (simple on/off) for
+ * huge_pages_status, even if there are multiple shared memory segments: all
+ * segments either use huge pages or not, there is no mix of segments with
+ * different page size. The latter might be actually beneficial, in particular
+ * because only some segments may require large amount of memory, but for now
+ * we go with a simple solution.
+ */
+void
+PrepareHugePages()
+{
+ void *ptr = MAP_FAILED;
+
+ /* Reset to handle reinitialization */
+ next_free_segment = 0;
+
+ /* Complain if hugepages demanded but we can't possibly support them */
+#if !defined(MAP_HUGETLB)
+ if (huge_pages == HUGE_PAGES_ON)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("huge pages not supported on this platform")));
+#else
+ if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ {
+ Size hugepagesize, total_size = 0;
+ int mmap_flags;
+
+ GetHugePageSize(&hugepagesize, &mmap_flags, NULL);
+
+ /*
+ * Figure out how much memory is needed for all segments, keeping in
+ * mind that for every segment this value will be rounding up by the
+ * huge page size. The resulting value will be used to probe memory and
+ * decide whether we will allocate huge pages or not.
+ */
+ for(int segment = 0; segment < ANON_MAPPINGS; segment++)
+ {
+ int numSemas;
+ Size segment_size = CalculateShmemSize(&numSemas, segment);
+
+ if (segment_size % hugepagesize != 0)
+ segment_size += hugepagesize - (segment_size % hugepagesize);
+
+ total_size += segment_size;
+ }
+
+ /* Map total amount of memory to test its availability. */
+ elog(DEBUG1, "reserving space: probe mmap(%zu) with MAP_HUGETLB",
+ total_size);
+ ptr = mmap(NULL, total_size, PROT_NONE,
+ PG_MMAP_FLAGS | MAP_ANONYMOUS | mmap_flags, -1, 0);
+ }
+#endif
+
+ /*
+ * Report whether huge pages are in use. This needs to be tracked before
+ * creating shared memory segments.
+ */
+ SetConfigOption("huge_pages_status", (ptr == MAP_FAILED) ? "off" : "on",
+ PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+ huge_pages_on = ptr != MAP_FAILED;
+}
+
/*
* AnonymousShmemDetach --- detach from an anonymous mmap'd block
* (called as an on_shmem_exit callback, hence funny argument list)
@@ -746,7 +926,7 @@ PGSharedMemoryCreate(Size size,
void *memAddress;
PGShmemHeader *hdr;
struct stat statbuf;
- Size sysvsize;
+ Size sysvsize, total_reserved;
AnonymousMapping *mapping = &Mappings[next_free_segment];
/*
@@ -760,14 +940,6 @@ PGSharedMemoryCreate(Size size,
errmsg("could not stat data directory \"%s\": %m",
DataDir)));
- /* Complain if hugepages demanded but we can't possibly support them */
-#if !defined(MAP_HUGETLB)
- if (huge_pages == HUGE_PAGES_ON)
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("huge pages not supported on this platform")));
-#endif
-
/* For now, we don't support huge pages in SysV memory */
if (huge_pages == HUGE_PAGES_ON && shared_memory_type != SHMEM_TYPE_MMAP)
ereport(ERROR,
@@ -776,8 +948,16 @@ PGSharedMemoryCreate(Size size,
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+
+ /* Prepare the mapping information */
mapping->shmem_size = size;
mapping->shmem_segment = next_free_segment;
+ total_reserved = (Size) MaxAvailableMemory * BLCKSZ;
+ mapping->shmem_reserved = total_reserved * SHMEM_RESIZE_RATIO[next_free_segment];
+
+ /* Round up to be a multiple of BLCKSZ */
+ mapping->shmem_reserved = mapping->shmem_reserved + BLCKSZ -
+ (mapping->shmem_reserved % BLCKSZ);
if (shared_memory_type == SHMEM_TYPE_MMAP)
{
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index 4dee856d6bd..732fedee87e 100644
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -627,7 +627,7 @@ pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
* use GetLargePageMinimum() instead.
*/
void
-GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+GetHugePageSize(Size *hugepagesize, int *mmap_flags, int *memfd_flags)
{
if (hugepagesize)
*hugepagesize = 0;
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 8b38e985327..b60f7ef9ce2 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -206,6 +206,9 @@ CreateSharedMemoryAndSemaphores(void)
Assert(!IsUnderPostmaster);
+ /* Decide if we use huge pages or regular size pages */
+ PrepareHugePages();
+
for(int segment = 0; segment < ANON_MAPPINGS; segment++)
{
/* Compute the size of the shared-memory block */
@@ -377,7 +380,7 @@ InitializeShmemGUCs(void)
/*
* Calculate the number of huge pages required.
*/
- GetHugePageSize(&hp_size, NULL);
+ GetHugePageSize(&hp_size, NULL, NULL);
if (hp_size != 0)
{
Size hp_required;
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 72255a1c5ca..8d025f0e907 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -817,7 +817,7 @@ pg_get_shmem_pagesize(void)
Assert(huge_pages_status != HUGE_PAGES_UNKNOWN);
if (huge_pages_status == HUGE_PAGES_ON)
- GetHugePageSize(&os_page_size, NULL);
+ GetHugePageSize(&os_page_size, NULL, NULL);
return os_page_size;
}
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index d31cb45a058..90d3feb547c 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -140,6 +140,7 @@ int max_parallel_maintenance_workers = 2;
* register background workers.
*/
int NBuffers = 16384;
+int MaxAvailableMemory = 524288;
int MaxConnections = 100;
int max_worker_processes = 8;
int max_parallel_workers = 8;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f04bfedb2fd..a221e446d6a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2376,6 +2376,20 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"max_available_memory", PGC_SIGHUP, RESOURCES_MEM,
+ gettext_noop("Sets the upper limit for the shared_buffers value."),
+ gettext_noop("Shared memory could be resized at runtime, this "
+ "parameters sets the upper limit for it, beyond which "
+ "resizing would not be supported. Normally this value "
+ "would be the same as the total available memory."),
+ GUC_UNIT_BLOCKS
+ },
+ &MaxAvailableMemory,
+ 524288, 16, INT_MAX / 2,
+ NULL, NULL, NULL
+ },
+
{
{"vacuum_buffer_usage_limit", PGC_USERSET, RESOURCES_MEM,
gettext_noop("Sets the buffer pool size for VACUUM, ANALYZE, and autovacuum."),
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 1bef98471c3..a0c37a7749e 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -173,6 +173,7 @@ extern PGDLLIMPORT char *DataDir;
extern PGDLLIMPORT int data_directory_mode;
extern PGDLLIMPORT int NBuffers;
+extern PGDLLIMPORT int MaxAvailableMemory;
extern PGDLLIMPORT int MaxBackends;
extern PGDLLIMPORT int MaxConnections;
extern PGDLLIMPORT int max_worker_processes;
diff --git a/src/include/portability/mem.h b/src/include/portability/mem.h
index ef9800732d9..40588ff6968 100644
--- a/src/include/portability/mem.h
+++ b/src/include/portability/mem.h
@@ -38,7 +38,7 @@
#define MAP_NOSYNC 0
#endif
-#define PG_MMAP_FLAGS (MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
+#define PG_MMAP_FLAGS (MAP_SHARED|MAP_HASSEMAPHORE)
/* Some really old systems don't define MAP_FAILED. */
#ifndef MAP_FAILED
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 2348c59b5a0..79b0b1ef9eb 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -61,6 +61,7 @@ extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
extern PGDLLIMPORT int huge_page_size;
extern PGDLLIMPORT int huge_pages_status;
+extern PGDLLIMPORT int MaxAvailableMemory;
/* Possible values for huge_pages and huge_pages_status */
typedef enum
@@ -104,7 +105,9 @@ extern PGShmemHeader *PGSharedMemoryCreate(Size size,
PGShmemHeader **shim);
extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
-extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
+extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
+ int *memfd_flags);
+void PrepareHugePages(void);
/* The main segment, contains everything except buffer blocks and related data. */
#define MAIN_SHMEM_SEGMENT 0
--
2.49.0
[text/plain] v5-0006-Introduce-multiple-shmem-segments-for-shared-buff.patch (11.6K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/7-v5-0006-Introduce-multiple-shmem-segments-for-shared-buff.patch)
download | inline diff:
From f23d42ef1ccdb28b751a8f12c7737002def4e674 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 11:22:02 +0200
Subject: [PATCH v5 06/10] Introduce multiple shmem segments for shared buffers
Add more shmem segments to split shared buffers into following chunks:
* BUFFERS_SHMEM_SEGMENT: contains buffer blocks
* BUFFER_DESCRIPTORS_SHMEM_SEGMENT: contains buffer descriptors
* BUFFER_IOCV_SHMEM_SEGMENT: contains condition variables for buffers
* CHECKPOINT_BUFFERS_SHMEM_SEGMENT: contains checkpoint buffer ids
* STRATEGY_SHMEM_SEGMENT: contains buffer strategy status
Size of the corresponding shared data directly depends on NBuffers,
meaning that if we would like to change NBuffers, they have to be
resized correspondingly. Placing each of them in a separate shmem
segment allows to achieve that.
There are some asumptions made about each of shmem segments upper size
limit. The buffer blocks have the largest, while the rest claim less
extra room for resize. Ideally those limits have to be deduced from the
maximum allowed shared memory.
---
src/backend/port/sysv_shmem.c | 24 +++++++-
src/backend/storage/buffer/buf_init.c | 79 +++++++++++++++++---------
src/backend/storage/buffer/buf_table.c | 6 +-
src/backend/storage/buffer/freelist.c | 5 +-
src/backend/storage/ipc/ipci.c | 2 +-
src/include/storage/bufmgr.h | 2 +-
src/include/storage/pg_shmem.h | 24 +++++++-
7 files changed, 105 insertions(+), 37 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 363ddfd1fca..dac011b766b 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -139,10 +139,18 @@ static int next_free_segment = 0;
*
* The reserved space for each segment is calculated as a fraction of the total
* reserved space (MaxAvailableMemory), as specified in the SHMEM_RESIZE_RATIO
- * array.
+ * array. E.g. we allow BUFFERS_SHMEM_SEGMENT to take up to 60% of the whole
+ * space when resizing, based on the fact that it most likely will be the main
+ * consumer of this memory. Those numbers are pulled out of thin air for now,
+ * makes sense to evaluate them more precise.
*/
-static double SHMEM_RESIZE_RATIO[1] = {
- 1.0, /* MAIN_SHMEM_SLOT */
+static double SHMEM_RESIZE_RATIO[6] = {
+ 0.1, /* MAIN_SHMEM_SEGMENT */
+ 0.6, /* BUFFERS_SHMEM_SEGMENT */
+ 0.1, /* BUFFER_DESCRIPTORS_SHMEM_SEGMENT */
+ 0.1, /* BUFFER_IOCV_SHMEM_SEGMENT */
+ 0.05, /* CHECKPOINT_BUFFERS_SHMEM_SEGMENT */
+ 0.05, /* STRATEGY_SHMEM_SEGMENT */
};
/*
@@ -167,6 +175,16 @@ MappingName(int shmem_segment)
{
case MAIN_SHMEM_SEGMENT:
return "main";
+ case BUFFERS_SHMEM_SEGMENT:
+ return "buffers";
+ case BUFFER_DESCRIPTORS_SHMEM_SEGMENT:
+ return "descriptors";
+ case BUFFER_IOCV_SHMEM_SEGMENT:
+ return "iocv";
+ case CHECKPOINT_BUFFERS_SHMEM_SEGMENT:
+ return "checkpoint";
+ case STRATEGY_SHMEM_SEGMENT:
+ return "strategy";
default:
return "unknown";
}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index ed1dc488a42..bd68b69ee98 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -62,7 +62,10 @@ CkptSortItem *CkptBufferIds;
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend).
+ * postmaster, or in a standalone backend). Size of data structures initialized
+ * here depends on NBuffers, and to be able to change NBuffers without a
+ * restart we store each structure into a separate shared memory segment, which
+ * could be resized on demand.
*/
void
BufferManagerShmemInit(void)
@@ -74,22 +77,22 @@ BufferManagerShmemInit(void)
/* Align descriptors to a cacheline boundary. */
BufferDescriptors = (BufferDescPadded *)
- ShmemInitStruct("Buffer Descriptors",
+ ShmemInitStructInSegment("Buffer Descriptors",
NBuffers * sizeof(BufferDescPadded),
- &foundDescs);
+ &foundDescs, BUFFER_DESCRIPTORS_SHMEM_SEGMENT);
/* Align buffer pool on IO page size boundary. */
BufferBlocks = (char *)
TYPEALIGN(PG_IO_ALIGN_SIZE,
- ShmemInitStruct("Buffer Blocks",
+ ShmemInitStructInSegment("Buffer Blocks",
NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
- &foundBufs));
+ &foundBufs, BUFFERS_SHMEM_SEGMENT));
/* Align condition variables to cacheline boundary. */
BufferIOCVArray = (ConditionVariableMinimallyPadded *)
- ShmemInitStruct("Buffer IO Condition Variables",
+ ShmemInitStructInSegment("Buffer IO Condition Variables",
NBuffers * sizeof(ConditionVariableMinimallyPadded),
- &foundIOCV);
+ &foundIOCV, BUFFER_IOCV_SHMEM_SEGMENT);
/*
* The array used to sort to-be-checkpointed buffer ids is located in
@@ -99,8 +102,9 @@ BufferManagerShmemInit(void)
* painful.
*/
CkptBufferIds = (CkptSortItem *)
- ShmemInitStruct("Checkpoint BufferIds",
- NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+ ShmemInitStructInSegment("Checkpoint BufferIds",
+ NBuffers * sizeof(CkptSortItem), &foundBufCkpt,
+ CHECKPOINT_BUFFERS_SHMEM_SEGMENT);
if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
{
@@ -156,33 +160,54 @@ BufferManagerShmemInit(void)
* BufferManagerShmemSize
*
* compute the size of shared memory for the buffer pool including
- * data pages, buffer descriptors, hash tables, etc.
+ * data pages, buffer descriptors, hash tables, etc. based on the
+ * shared memory segment. The main segment must not allocate anything
+ * related to buffers, every other segment will receive part of the
+ * data.
*/
Size
-BufferManagerShmemSize(void)
+BufferManagerShmemSize(int shmem_segment)
{
Size size = 0;
- /* size of buffer descriptors */
- size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
- /* to allow aligning buffer descriptors */
- size = add_size(size, PG_CACHE_LINE_SIZE);
+ if (shmem_segment == MAIN_SHMEM_SEGMENT)
+ return size;
- /* size of data pages, plus alignment padding */
- size = add_size(size, PG_IO_ALIGN_SIZE);
- size = add_size(size, mul_size(NBuffers, BLCKSZ));
+ if (shmem_segment == BUFFER_DESCRIPTORS_SHMEM_SEGMENT)
+ {
+ /* size of buffer descriptors */
+ size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+ /* to allow aligning buffer descriptors */
+ size = add_size(size, PG_CACHE_LINE_SIZE);
+ }
- /* size of stuff controlled by freelist.c */
- size = add_size(size, StrategyShmemSize());
+ if (shmem_segment == BUFFERS_SHMEM_SEGMENT)
+ {
+ /* size of data pages, plus alignment padding */
+ size = add_size(size, PG_IO_ALIGN_SIZE);
+ size = add_size(size, mul_size(NBuffers, BLCKSZ));
+ }
- /* size of I/O condition variables */
- size = add_size(size, mul_size(NBuffers,
- sizeof(ConditionVariableMinimallyPadded)));
- /* to allow aligning the above */
- size = add_size(size, PG_CACHE_LINE_SIZE);
+ if (shmem_segment == STRATEGY_SHMEM_SEGMENT)
+ {
+ /* size of stuff controlled by freelist.c */
+ size = add_size(size, StrategyShmemSize());
+ }
- /* size of checkpoint sort array in bufmgr.c */
- size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+ if (shmem_segment == BUFFER_IOCV_SHMEM_SEGMENT)
+ {
+ /* size of I/O condition variables */
+ size = add_size(size, mul_size(NBuffers,
+ sizeof(ConditionVariableMinimallyPadded)));
+ /* to allow aligning the above */
+ size = add_size(size, PG_CACHE_LINE_SIZE);
+ }
+
+ if (shmem_segment == CHECKPOINT_BUFFERS_SHMEM_SEGMENT)
+ {
+ /* size of checkpoint sort array in bufmgr.c */
+ size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+ }
return size;
}
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index a50955d5286..a9952b36eba 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -22,6 +22,7 @@
#include "postgres.h"
#include "storage/buf_internals.h"
+#include "storage/pg_shmem.h"
/* entry for buffer lookup hashtable */
typedef struct
@@ -59,10 +60,11 @@ InitBufTable(int size)
info.entrysize = sizeof(BufferLookupEnt);
info.num_partitions = NUM_BUFFER_PARTITIONS;
- SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
+ SharedBufHash = ShmemInitHashInSegment("Shared Buffer Lookup Table",
size, size,
&info,
- HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
+ HASH_ELEM | HASH_BLOBS | HASH_PARTITION,
+ STRATEGY_SHMEM_SEGMENT);
}
/*
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 01909be0272..bd390f2709d 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -19,6 +19,7 @@
#include "port/atomics.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#define INT_ACCESS_ONCE(var) ((int)(*((volatile int *)&(var))))
@@ -491,9 +492,9 @@ StrategyInitialize(bool init)
* Get or create the shared strategy control block
*/
StrategyControl = (BufferStrategyControl *)
- ShmemInitStruct("Buffer Strategy Status",
+ ShmemInitStructInSegment("Buffer Strategy Status",
sizeof(BufferStrategyControl),
- &found);
+ &found, STRATEGY_SHMEM_SEGMENT);
if (!found)
{
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index b60f7ef9ce2..2dbd81afc87 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -113,7 +113,7 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
sizeof(ShmemIndexEnt)));
size = add_size(size, dsm_estimate_size());
size = add_size(size, DSMRegistryShmemSize());
- size = add_size(size, BufferManagerShmemSize());
+ size = add_size(size, BufferManagerShmemSize(shmem_segment));
size = add_size(size, LockManagerShmemSize());
size = add_size(size, PredicateLockShmemSize());
size = add_size(size, ProcGlobalShmemSize());
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 41fdc1e7693..edac9db6a12 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -318,7 +318,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
/* in buf_init.c */
extern void BufferManagerShmemInit(void);
-extern Size BufferManagerShmemSize(void);
+extern Size BufferManagerShmemSize(int);
/* in localbuf.c */
extern void AtProcExit_LocalBuffers(void);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 79b0b1ef9eb..a7b275b4db9 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -52,7 +52,7 @@ typedef struct ShmemSegment
} ShmemSegment;
/* Number of available segments for anonymous memory mappings */
-#define ANON_MAPPINGS 1
+#define ANON_MAPPINGS 6
extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
@@ -109,7 +109,29 @@ extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
int *memfd_flags);
void PrepareHugePages(void);
+/*
+ * To be able to dynamically resize largest parts of the data stored in shared
+ * memory, we split it into multiple shared memory mappings segments. Each
+ * segment contains only certain part of the data, which size depends on
+ * NBuffers.
+ */
+
/* The main segment, contains everything except buffer blocks and related data. */
#define MAIN_SHMEM_SEGMENT 0
+/* Buffer blocks */
+#define BUFFERS_SHMEM_SEGMENT 1
+
+/* Buffer descriptors */
+#define BUFFER_DESCRIPTORS_SHMEM_SEGMENT 2
+
+/* Condition variables for buffers */
+#define BUFFER_IOCV_SHMEM_SEGMENT 3
+
+/* Checkpoint BufferIds */
+#define CHECKPOINT_BUFFERS_SHMEM_SEGMENT 4
+
+/* Buffer strategy status */
+#define STRATEGY_SHMEM_SEGMENT 5
+
#endif /* PG_SHMEM_H */
--
2.49.0
[text/plain] v5-0007-Allow-to-resize-shared-memory-without-restart.patch (41.3K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/8-v5-0007-Allow-to-resize-shared-memory-without-restart.patch)
download | inline diff:
From c5717c5b68439abf4488fc3e1c2e47a94c6cd9f3 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Tue, 17 Jun 2025 14:16:55 +0200
Subject: [PATCH v5 07/10] Allow to resize shared memory without restart
Add assing hook for shared_buffers to resize shared memory using space,
introduced in the previous commits without requiring PostgreSQL restart.
Essentially the implementation is based on two mechanisms: a
ProcSignalBarrier is used to make sure all processes are starting the
resize procedure simultaneously, and a global Barrier is used to
coordinate after that and make sure all finished processes are waiting
for others that are in progress.
The resize process looks like this:
* The GUC assign hook sets a flag to let the Postmaster know that resize
was requested.
* Postmaster verifies the flag in the event loop, and starts the resize
by emitting a ProcSignal barrier.
* All processes, that participate in ProcSignal mechanism, begin to
process ProcSignal barrier. First a process waits until all processes
have confirmed they received the message and can start simultaneously.
* Every process recalculates shared memory size based on the new
NBuffers, adjusts its size using ftruncate and adjust reservation
permissions with mprotect. One elected process signals the postmaster
to do the same.
* When finished, every process waits on a global ShmemControl barrier,
untill all others are finished as well. This way we ensure three
stages with clear boundaries: before the resize, when all processes
use old NBuffers; during the resize, when processes have mix of old
and new NBuffers, and wait until it's done; after the resize, when all
processes use new NBuffers.
* After all processes are using new value, one of them will initialize
new shared structures (buffer blocks, descriptors, etc) as needed and
broadcast new value of NBuffers via ShmemControl in shared memory.
Other backends are waiting for this operation to finish as well. Then
the barrier is lifted and everything goes as usual.
Since resizing takes time, we need to take into account that during that time:
- New backends can be spawned. They will check status of the barrier
early during the bootstrap, and wait until everything is over to work
with the new NBuffers value.
- Old backends can exit before attempting to resize. Synchronization
used between backends relies on ProcSignalBarrier and waits for all
participants received the message at the beginning to gather all
existing backends.
- Some backends might be blocked and not responsing either before or
after receiving the message. In the first case such backend still
have ProcSignalSlot and should be waited for, in the second case
shared barrier will make sure we still waiting for those backends. In
any case there is an unbounded wait.
- Backends might join barrier in disjoint groups with some time in
between. That means that relying only on the shared dynamic barrier is
not enough -- it will only synchronize resize procedure withing those
groups. That's why we wait first for all participants of ProcSignal
mechanism who received the message.
Here is how it looks like after raising shared_buffers from 128 MB to
512 MB and calling pg_reload_conf():
-- 128 MB
7f87909fc000-7f8798248000 rw-s /memfd:strategy (deleted)
7f8798248000-7f879d6ca000 ---s /memfd:strategy (deleted)
7f879d6ca000-7f87a4e84000 rw-s /memfd:checkpoint (deleted)
7f87a4e84000-7f87aa398000 ---s /memfd:checkpoint (deleted)
7f87aa398000-7f87b1b42000 rw-s /memfd:iocv (deleted)
7f87b1b42000-7f87c3d32000 ---s /memfd:iocv (deleted)
7f87c3d32000-7f87cb59c000 rw-s /memfd:descriptors (deleted)
7f87cb59c000-7f87dd6cc000 ---s /memfd:descriptors (deleted)
7f87dd6cc000-7f87ece38000 rw-s /memfd:buffers (deleted)
^ buffers content, ~247 MB
7f87ece38000-7f8877066000 ---s /memfd:buffers (deleted)
^ reserved space, ~2210 MB
7f8877066000-7f887e7d0000 rw-s /memfd:main (deleted)
7f887e7d0000-7f8890a00000 ---s /memfd:main (deleted)
-- 512 MB
7f87909fc000-7f879866a000 rw-s /memfd:strategy (deleted)
7f879866a000-7f879d6ca000 ---s /memfd:strategy (deleted)
7f879d6ca000-7f87a50f4000 rw-s /memfd:checkpoint (deleted)
7f87a50f4000-7f87aa398000 ---s /memfd:checkpoint (deleted)
7f87aa398000-7f87b1d82000 rw-s /memfd:iocv (deleted)
7f87b1d82000-7f87c3d32000 ---s /memfd:iocv (deleted)
7f87c3d32000-7f87cba1c000 rw-s /memfd:descriptors (deleted)
7f87cba1c000-7f87dd6cc000 ---s /memfd:descriptors (deleted)
7f87dd6cc000-7f8804fb8000 rw-s /memfd:buffers (deleted)
^ buffers content, ~632 MB
7f8804fb8000-7f8877066000 ---s /memfd:buffers (deleted)
^ reserved space, ~1824 MB
7f8877066000-7f887e950000 rw-s /memfd:main (deleted)
7f887e950000-7f8890a00000 ---s /memfd:main (deleted)
The implementation supports only increasing of shared_buffers. For
decreasing the value a similar procedure is needed. But the buffer
blocks with data have to be drained first, so that the actual data set
fits into the new smaller space.
From experiment it turns out that shared mappings have to be extended
separately for each process that uses them. Another rough edge is that a
backend blocked on ReadCommand will not apply shared_buffers change
until it receives something.
Authors: Dmitrii Dolgov, Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 446 ++++++++++++++++++
src/backend/postmaster/checkpointer.c | 12 +-
src/backend/postmaster/postmaster.c | 18 +
src/backend/storage/buffer/buf_init.c | 74 +--
src/backend/storage/ipc/ipci.c | 18 +-
src/backend/storage/ipc/procsignal.c | 46 ++
src/backend/storage/ipc/shmem.c | 23 +-
src/backend/tcop/postgres.c | 10 +
.../utils/activity/wait_event_names.txt | 3 +
src/backend/utils/misc/guc_tables.c | 4 +-
src/include/storage/bufmgr.h | 2 +-
src/include/storage/ipc.h | 3 +
src/include/storage/lwlocklist.h | 1 +
src/include/storage/pg_shmem.h | 26 +
src/include/storage/pmsignal.h | 1 +
src/include/storage/procsignal.h | 1 +
src/tools/pgindent/typedefs.list | 1 +
17 files changed, 644 insertions(+), 45 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index dac011b766b..b3c90d15d52 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -30,13 +30,19 @@
#include "miscadmin.h"
#include "port/pg_bitutils.h"
#include "portability/mem.h"
+#include "storage/bufmgr.h"
#include "storage/dsm.h"
#include "storage/fd.h"
#include "storage/ipc.h"
+#include "storage/lwlock.h"
#include "storage/pg_shmem.h"
+#include "storage/pmsignal.h"
+#include "storage/procsignal.h"
+#include "storage/shmem.h"
#include "utils/guc.h"
#include "utils/guc_hooks.h"
#include "utils/pidfile.h"
+#include "utils/wait_event.h"
/*
@@ -107,6 +113,13 @@ typedef struct AnonymousMapping
static AnonymousMapping Mappings[ANON_MAPPINGS];
+/* Flag telling postmaster that resize is needed */
+volatile bool pending_pm_shmem_resize = false;
+
+/* Keeps track of the previous NBuffers value */
+static int NBuffersOld = -1;
+static int NBuffersPending = -1;
+
/* Keeps track of used mapping segments */
static int next_free_segment = 0;
@@ -161,6 +174,49 @@ static double SHMEM_RESIZE_RATIO[6] = {
*/
static bool huge_pages_on = false;
+/*
+ * Flag telling that we have prepared the memory layout to be resizable. If
+ * false after all shared memory segments creation, it means we failed to setup
+ * needed layout and falled back to the regular non-resizable approach.
+ */
+static bool shmem_resizable = false;
+
+/*
+ * Currently broadcasted value of NBuffers in shared memory.
+ *
+ * Most of the time this value is going to be equal to NBuffers. But if
+ * postmaster is resizing shared memory and a new backend was created
+ * at the same time, there is a possibility for the new backend to inherit the
+ * old NBuffers value, but miss the resize signal if ProcSignal infrastructure
+ * was not initialized yet. Consider this situation:
+ *
+ * Postmaster ------> New Backend
+ * | |
+ * | Launch
+ * | |
+ * | Inherit NBuffers
+ * | |
+ * Resize NBuffers |
+ * | |
+ * Emit Barrier |
+ * | Init ProcSignal
+ * | |
+ * Finish resize |
+ * | |
+ * New NBuffers Old NBuffers
+ *
+ * In this case the backend is not yet ready to receive a signal from
+ * EmitProcSignalBarrier, and will be ignored. The same happens if ProcSignal
+ * is initialized even later, after the resizing was finished.
+ *
+ * To address resulting inconsistency, postmaster broadcasts the current
+ * NBuffers value via shared memory. Every new backend has to verify this value
+ * before it will access the buffer pool: if it differs from its own value,
+ * this indicates a shared memory resize has happened and the backend has to
+ * first synchronize with rest of the pack.
+ */
+ShmemControl *ShmemCtrl = NULL;
+
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
@@ -924,6 +980,349 @@ AnonymousShmemDetach(int status, Datum arg)
}
}
+/*
+ * Resize all shared memory segments based on the current NBuffers value, which
+ * is is applied from NBuffersPending. The actual segment resizing is done via
+ * ftruncate, which will fail if is not sufficient space to expand the anon
+ * file. When finished, based on the new and old values initialize new buffer
+ * blocks if any.
+ *
+ * If reinitializing took place, as the last step this function does buffers
+ * reinitialization as well and broadcasts the new value of NSharedBuffers. All
+ * of that needs to be done only by one backend, the first one that managed to
+ * grab the ShmemResizeLock.
+ */
+bool
+AnonymousShmemResize(void)
+{
+ int numSemas;
+ bool reinit = false;
+ int mmap_flags = PG_MMAP_FLAGS;
+ Size hugepagesize;
+
+ NBuffers = NBuffersPending;
+
+ elog(DEBUG1, "Resize shmem from %d to %d", NBuffersOld, NBuffers);
+
+ /*
+ * XXX: Where to reset the flag is still an open question. E.g. do we
+ * consider a no-op when NBuffers is equal to NBuffersOld a genuine resize
+ * and reset the flag?
+ */
+ pending_pm_shmem_resize = false;
+
+ /*
+ * XXX: Currently only increasing of shared_buffers is supported. For
+ * decreasing something similar has to be done, but buffer blocks with
+ * data have to be drained first.
+ */
+ if(NBuffersOld > NBuffers)
+ return false;
+
+#ifndef MAP_HUGETLB
+ /* PrepareHugePages should have dealt with this case */
+ Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
+#else
+ if (huge_pages_on)
+ {
+ /* Make sure nothing is messed up */
+ Assert(huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY);
+
+ /* Round up the new size to a suitable large value */
+ GetHugePageSize(&hugepagesize, &mmap_flags, NULL);
+ }
+#endif
+
+ for(int i = 0; i < next_free_segment; i++)
+ {
+ /* Note that CalculateShmemSize indirectly depends on NBuffers */
+ Size new_size = CalculateShmemSize(&numSemas, i);
+ AnonymousMapping *m = &Mappings[i];
+
+#ifdef MAP_HUGETLB
+ if (huge_pages_on && (new_size % hugepagesize != 0))
+ new_size += hugepagesize - (new_size % hugepagesize);
+#endif
+
+ if (m->shmem == NULL)
+ continue;
+
+ if (m->shmem_size == new_size)
+ continue;
+
+ if (m->shmem_reserved < new_size)
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+ errmsg("not enough shared memory is reserved"),
+ errhint("You may need to increase \"max_available_memory\".")));
+
+ elog(DEBUG1, "segment[%s]: resize from %zu to %zu at address %p",
+ MappingName(m->shmem_segment), m->shmem_size,
+ new_size, m->shmem);
+
+ /* Resize the backing anon file. */
+ if(ftruncate(m->segment_fd, new_size) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not truncase anonymous file for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ /* Adjust memory accessibility */
+ if(mprotect(m->shmem, new_size, PROT_READ | PROT_WRITE) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not mprotect anonymous shared memory for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ /* If shrinking, make reserved space unavailable again */
+ if(new_size < m->shmem_size &&
+ mprotect(m->shmem + new_size, m->shmem_size - new_size, PROT_NONE) == -1)
+ ereport(FATAL,
+ (errcode(ERRCODE_SYSTEM_ERROR),
+ errmsg("could not mprotect reserved shared memory for \"%s\": %m",
+ MappingName(m->shmem_segment))));
+
+ reinit = true;
+ m->shmem_size = new_size;
+ }
+
+ if (reinit)
+ {
+ if(IsUnderPostmaster &&
+ LWLockConditionalAcquire(ShmemResizeLock, LW_EXCLUSIVE))
+ {
+ /*
+ * If the new NBuffers was already broadcasted, the buffer pool was
+ * already initialized before.
+ *
+ * Since we're not on a hot path, we use lwlocks and do not need to
+ * involve memory barrier.
+ */
+ if(pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) != NBuffers)
+ {
+ /*
+ * Allow the first backend that managed to get the lock to
+ * reinitialize the new portion of buffer pool. Every other
+ * process will wait on the shared barrier for that to finish,
+ * since it's a part of the SHMEM_RESIZE_DONE phase.
+ *
+ * Note that it's enough when only one backend will do that,
+ * even the ShmemInitStruct part. The reason is that resized
+ * shared memory will maintain the same addresses, meaning that
+ * all the pointers are still valid, and we only need to update
+ * structures size in the ShmemIndex once -- any other backend
+ * will pick up this shared structure from the index.
+ *
+ * XXX: This is the right place for buffer eviction as well.
+ */
+ BufferManagerShmemInit(NBuffersOld);
+
+ /* If all fine, broadcast the new value */
+ pg_atomic_write_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
+ }
+
+ LWLockRelease(ShmemResizeLock);
+ }
+ }
+
+ return true;
+}
+
+/*
+ * We are asked to resize shared memory. Wait for all ProcSignal participants
+ * to join the barrier, then do the resize and wait on the barrier until all
+ * participating finish resizing as well -- otherwise we face danger of
+ * inconsistency between backends.
+ *
+ * XXX: If a backend is blocked on ReadCommand in PostgresMain, it will not
+ * proceed with AnonymousShmemResize after receiving SIGHUP, until something
+ * will be sent.
+ */
+bool
+ProcessBarrierShmemResize(Barrier *barrier)
+{
+ Assert(IsUnderPostmaster);
+
+ elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d",
+ NBuffersOld, NBuffersPending, pending_pm_shmem_resize);
+
+ /* Wait until we have seen the new NBuffers value */
+ if (!pending_pm_shmem_resize)
+ return false;
+
+ /*
+ * First thing to do after attaching to the barrier is to wait for others.
+ * We can't simply use BarrierArriveAndWait, because backends might arrive
+ * here in disjoint groups, e.g. first two backends, pause, then second two
+ * backends. If the resize is quick enough that can lead to a situation
+ * when the first group is already finished before the second has appeared,
+ * and the barrier will only synchonize withing those groups.
+ */
+ if (BarrierAttach(barrier) == SHMEM_RESIZE_REQUESTED)
+ WaitForProcSignalBarrierReceived(
+ pg_atomic_read_u64(&ShmemCtrl->Generation));
+
+ /*
+ * Now start the procedure, and elect one backend to ping postmaster to do
+ * the same.
+ *
+ * XXX: If we need to be able to abort resizing, this has to be done later,
+ * after the SHMEM_RESIZE_DONE.
+ */
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+ {
+ Assert(IsUnderPostmaster);
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
+ }
+
+ AnonymousShmemResize();
+
+ /* The second phase means the resize has finished, SHMEM_RESIZE_DONE */
+ BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_DONE);
+
+ BarrierDetach(barrier);
+ return true;
+}
+
+/*
+ * GUC assign hook for shared_buffers. It's recommended for an assign hook to
+ * be as minimal as possible, thus we just request shared memory resize and
+ * remember the previous value.
+ */
+void
+assign_shared_buffers(int newval, void *extra, bool *pending)
+{
+ elog(DEBUG1, "Received SIGHUP for shmem resizing");
+
+ /* Request shared memory resize only when it was initialized */
+ if (next_free_segment != 0)
+ {
+ pending_pm_shmem_resize = true;
+ *pending = true;
+ NBuffersPending = newval;
+ }
+
+ NBuffersOld = NBuffers;
+}
+
+/*
+ * Test if we have somehow missed a shmem resize signal and NBuffers value
+ * differs from NSharedBuffers. If yes, catchup and do resize.
+ */
+void
+AdjustShmemSize(void)
+{
+ uint32 NSharedBuffers = pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers);
+
+ if (NSharedBuffers != NBuffers)
+ {
+ /*
+ * If the broadcasted shared_buffers is different from the one we see,
+ * it could be that the backend has missed a resize signal. To avoid
+ * any inconsistency, adjust the shared mappings, before having a
+ * chance to access the buffer pool.
+ */
+ ereport(LOG,
+ (errmsg("shared_buffers has been changed from %d to %d, "
+ "resize shared memory",
+ NBuffers, NSharedBuffers)));
+ NBuffers = NSharedBuffers;
+ AnonymousShmemResize();
+ }
+}
+
+/*
+ * Start resizing procedure, making sure all existing processes will have
+ * consistent view of shared memory size. Must be called only in postmaster.
+ */
+void
+CoordinateShmemResize(void)
+{
+ elog(DEBUG1, "Coordinating shmem resize from %d to %d",
+ NBuffersOld, NBuffers);
+ Assert(!IsUnderPostmaster);
+
+ /*
+ * We use dynamic barrier to help dealing with backends that were spawned
+ * during the resize.
+ */
+ BarrierInit(&ShmemCtrl->Barrier, 0);
+
+ /*
+ * If the value did not change, or shared memory segments are not
+ * initialized yet, skip the resize.
+ */
+ if (NBuffersPending == NBuffersOld || next_free_segment == 0)
+ {
+ elog(DEBUG1, "Skip resizing, new %d, old %d, free segment %d",
+ NBuffers, NBuffersOld, next_free_segment);
+ return;
+ }
+
+ /*
+ * Shared memory resize requires some coordination done by postmaster,
+ * and consists of three phases:
+ *
+ * - Before the resize all existing backends have the same old NBuffers.
+ * - When resize is in progress, backends are expected to have a
+ * mixture of old a new values. They're not allowed to touch buffer
+ * pool during this time frame.
+ * - After resize has been finished, all existing backends, that can access
+ * the buffer pool, are expected to have the same new value of NBuffers.
+ *
+ * Those phases are ensured by joining the shared barrier associated with
+ * the procedure. Since resizing takes time, we need to take into account
+ * that during that time:
+ *
+ * - New backends can be spawned. They will check status of the barrier
+ * early during the bootstrap, and wait until everything is over to work
+ * with the new NBuffers value.
+ *
+ * - Old backends can exit before attempting to resize. Synchronization
+ * used between backends relies on ProcSignalBarrier and waits for all
+ * participants received the message at the beginning to gather all
+ * existing backends.
+ *
+ * - Some backends might be blocked and not responsing either before or
+ * after receiving the message. In the first case such backend still
+ * have ProcSignalSlot and should be waited for, in the second case
+ * shared barrier will make sure we still waiting for those backends. In
+ * any case there is an unbounded wait.
+ *
+ * - Backends might join barrier in disjoint groups with some time in
+ * between. That means that relying only on the shared dynamic barrier is
+ * not enough -- it will only synchronize resize procedure withing those
+ * groups. That's why we wait first for all participants of ProcSignal
+ * mechanism who received the message.
+ */
+ elog(DEBUG1, "Emit a barrier for shmem resizing");
+ pg_atomic_init_u64(&ShmemCtrl->Generation,
+ EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SHMEM_RESIZE));
+
+ /* To order everything after setting Generation value */
+ pg_memory_barrier();
+
+ /*
+ * After that postmaster waits for PMSIGNAL_SHMEM_RESIZE as a sign that all
+ * the rest of the pack has started the procedure and it can resize shared
+ * memory as well.
+ *
+ * Normally we would call WaitForProcSignalBarrier here to wait until every
+ * backend has reported on the ProcSignalBarrier. But for shared memory
+ * resize we don't need this, as every participating backend will
+ * synchronize on the ProcSignal barrier. In fact even if we would like to
+ * wait here, it wouldn't be possible -- we're in the postmaster, without
+ * any waiting infrastructure available.
+ *
+ * If at some point it will turn out that waiting is essential, we would
+ * need to consider some alternatives. E.g. it could be a designated
+ * coordination process, which is not a postmaster. Another option would be
+ * to introduce a CoordinateShmemResize lock and allow only one process to
+ * take it (this probably would have to be something different than
+ * LWLocks, since they block interrupts, and coordination relies on them).
+ */
+}
+
/*
* PGSharedMemoryCreate
*
@@ -1239,3 +1638,50 @@ PGSharedMemoryDetach(void)
}
}
}
+
+void
+WaitOnShmemBarrier()
+{
+ Barrier *barrier = &ShmemCtrl->Barrier;
+
+ /* Nothing to do if resizing is not started */
+ if (BarrierPhase(barrier) < SHMEM_RESIZE_START)
+ return;
+
+ BarrierAttach(barrier);
+
+ /* Otherwise wait through all available phases */
+ while (BarrierPhase(barrier) < SHMEM_RESIZE_DONE)
+ {
+ ereport(LOG, (errmsg("ProcSignal barrier is in phase %d, waiting",
+ BarrierPhase(barrier))));
+
+ BarrierArriveAndWait(barrier, 0);
+ }
+
+ BarrierDetach(barrier);
+}
+
+void
+ShmemControlInit(void)
+{
+ bool foundShmemCtrl;
+
+ ShmemCtrl = (ShmemControl *)
+ ShmemInitStruct("Shmem Control", sizeof(ShmemControl),
+ &foundShmemCtrl);
+
+ if (!foundShmemCtrl)
+ {
+ /*
+ * The barrier is missing here, it will be initialized right before
+ * starting the resizing process as a convenient way to reset it.
+ */
+
+ /* Initialize with the currently known value */
+ pg_atomic_init_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
+
+ /* shmem_resizable should be initialized by now */
+ ShmemCtrl->Resizable = shmem_resizable;
+ }
+}
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index fda91ffd1ce..ab08e1a182b 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -638,9 +638,12 @@ CheckpointerMain(const void *startup_data, size_t startup_data_len)
static void
ProcessCheckpointerInterrupts(void)
{
- if (ProcSignalBarrierPending)
- ProcessProcSignalBarrier();
-
+ /*
+ * Reloading config can trigger further signals, complicating interrupts
+ * processing -- so let it run first.
+ *
+ * XXX: Is there any need in memory barrier after ProcessConfigFile?
+ */
if (ConfigReloadPending)
{
ConfigReloadPending = false;
@@ -660,6 +663,9 @@ ProcessCheckpointerInterrupts(void)
UpdateSharedMemoryConfig();
}
+ if (ProcSignalBarrierPending)
+ ProcessProcSignalBarrier();
+
/* Perform logging of memory contexts of this process */
if (LogMemoryContextPending)
ProcessLogMemoryContextInterrupt();
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 490f7ce3664..f0cb0098dcd 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -426,6 +426,7 @@ static void process_pm_pmsignal(void);
static void process_pm_child_exit(void);
static void process_pm_reload_request(void);
static void process_pm_shutdown_request(void);
+static void process_pm_shmem_resize(void);
static void dummy_handler(SIGNAL_ARGS);
static void CleanupBackend(PMChild *bp, int exitstatus);
static void HandleChildCrash(int pid, int exitstatus, const char *procname);
@@ -1694,6 +1695,9 @@ ServerLoop(void)
if (pending_pm_pmsignal)
process_pm_pmsignal();
+ if (pending_pm_shmem_resize)
+ process_pm_shmem_resize();
+
if (events[i].events & WL_SOCKET_ACCEPT)
{
ClientSocket s;
@@ -2039,6 +2043,17 @@ process_pm_reload_request(void)
}
}
+static void
+process_pm_shmem_resize(void)
+{
+ /*
+ * Failure to resize is considered to be fatal and will not be
+ * retried, which means we can disable pending flag right here.
+ */
+ pending_pm_shmem_resize = false;
+ CoordinateShmemResize();
+}
+
/*
* pg_ctl uses SIGTERM, SIGINT and SIGQUIT to request different types of
* shutdown.
@@ -3852,6 +3867,9 @@ process_pm_pmsignal(void)
request_state_update = true;
}
+ if (CheckPostmasterSignal(PMSIGNAL_SHMEM_RESIZE))
+ AnonymousShmemResize();
+
/*
* Try to advance postmaster's state machine, if a child requests it.
*/
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index bd68b69ee98..8c1ea623392 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -17,6 +17,7 @@
#include "storage/aio.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
+#include "storage/pg_shmem.h"
BufferDescPadded *BufferDescriptors;
char *BufferBlocks;
@@ -62,18 +63,28 @@ CkptSortItem *CkptBufferIds;
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
- * postmaster, or in a standalone backend). Size of data structures initialized
- * here depends on NBuffers, and to be able to change NBuffers without a
- * restart we store each structure into a separate shared memory segment, which
- * could be resized on demand.
+ * postmaster, or in a standalone backend) or during shared-memory resize. Size
+ * of data structures initialized here depends on NBuffers, and to be able to
+ * change NBuffers without a restart we store each structure into a separate
+ * shared memory segment, which could be resized on demand.
+ *
+ * FirstBufferToInit tells where to start initializing buffers. For
+ * initialization it always will be zero, but when resizing shared-memory it
+ * indicates the number of already initialized buffers.
+ *
+ * No locks are taking in this function, it is the caller responsibility to
+ * make sure only one backend can work with new buffers.
*/
void
-BufferManagerShmemInit(void)
+BufferManagerShmemInit(int FirstBufferToInit)
{
bool foundBufs,
foundDescs,
foundIOCV,
foundBufCkpt;
+ int i;
+ elog(DEBUG1, "BufferManagerShmemInit from %d to %d",
+ FirstBufferToInit, NBuffers);
/* Align descriptors to a cacheline boundary. */
BufferDescriptors = (BufferDescPadded *)
@@ -110,43 +121,44 @@ BufferManagerShmemInit(void)
{
/* should find all of these, or none of them */
Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
- /* note: this path is only taken in EXEC_BACKEND case */
- }
- else
- {
- int i;
-
/*
- * Initialize all the buffer headers.
+ * note: this path is only taken in EXEC_BACKEND case when initializing
+ * shared memory, or in all cases when resizing shared memory.
*/
- for (i = 0; i < NBuffers; i++)
- {
- BufferDesc *buf = GetBufferDescriptor(i);
+ }
- ClearBufferTag(&buf->tag);
+#ifndef EXEC_BACKEND
+ /*
+ * Initialize all the buffer headers.
+ */
+ for (i = FirstBufferToInit; i < NBuffers; i++)
+ {
+ BufferDesc *buf = GetBufferDescriptor(i);
- pg_atomic_init_u32(&buf->state, 0);
- buf->wait_backend_pgprocno = INVALID_PROC_NUMBER;
+ ClearBufferTag(&buf->tag);
- buf->buf_id = i;
+ pg_atomic_init_u32(&buf->state, 0);
+ buf->wait_backend_pgprocno = INVALID_PROC_NUMBER;
- pgaio_wref_clear(&buf->io_wref);
+ buf->buf_id = i;
- /*
- * Initially link all the buffers together as unused. Subsequent
- * management of this list is done by freelist.c.
- */
- buf->freeNext = i + 1;
+ pgaio_wref_clear(&buf->io_wref);
- LWLockInitialize(BufferDescriptorGetContentLock(buf),
- LWTRANCHE_BUFFER_CONTENT);
+ /*
+ * Initially link all the buffers together as unused. Subsequent
+ * management of this list is done by freelist.c.
+ */
+ buf->freeNext = i + 1;
- ConditionVariableInit(BufferDescriptorGetIOCV(buf));
- }
+ LWLockInitialize(BufferDescriptorGetContentLock(buf),
+ LWTRANCHE_BUFFER_CONTENT);
- /* Correct last entry of linked list */
- GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
+ ConditionVariableInit(BufferDescriptorGetIOCV(buf));
}
+#endif
+
+ /* Correct last entry of linked list */
+ GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2dbd81afc87..c5725f55120 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -84,6 +84,9 @@ RequestAddinShmemSpace(Size size)
*
* If num_semaphores is not NULL, it will be set to the number of semaphores
* required.
+ *
+ * XXX: Calculation for non main shared memory segments are incorrect, it
+ * includes more than needed for buffers only.
*/
Size
CalculateShmemSize(int *num_semaphores, int shmem_segment)
@@ -151,6 +154,14 @@ CalculateShmemSize(int *num_semaphores, int shmem_segment)
size = add_size(size, SlotSyncShmemSize());
size = add_size(size, AioShmemSize());
+ /*
+ * XXX: For some reason slightly more memory is needed for larger
+ * shared_buffers, but this size is enough for any large value I've tested
+ * with. Is it a mistake in how slots are split, or there was a hidden
+ * inconsistency in shmem calculation?
+ */
+ size = add_size(size, 1024 * 1024 * 100);
+
/* include additional requested shmem from preload libraries */
size = add_size(size, total_addin_request);
@@ -298,7 +309,7 @@ CreateOrAttachShmemStructs(void)
CommitTsShmemInit();
SUBTRANSShmemInit();
MultiXactShmemInit();
- BufferManagerShmemInit();
+ BufferManagerShmemInit(0);
/*
* Set up lock manager
@@ -310,6 +321,11 @@ CreateOrAttachShmemStructs(void)
*/
PredicateLockShmemInit();
+ /*
+ * Set up shared memory resize manager
+ */
+ ShmemControlInit();
+
/*
* Set up process table
*/
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index c6bec9be423..d7b56a18b24 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -27,6 +27,7 @@
#include "storage/condition_variable.h"
#include "storage/ipc.h"
#include "storage/latch.h"
+#include "storage/pg_shmem.h"
#include "storage/shmem.h"
#include "storage/sinval.h"
#include "storage/smgr.h"
@@ -113,6 +114,10 @@ static bool CheckProcSignal(ProcSignalReason reason);
static void CleanupProcSignalState(int status, Datum arg);
static void ResetProcSignalBarrierBits(uint32 flags);
+#ifdef DEBUG_SHMEM_RESIZE
+bool delay_proc_signal_init = false;
+#endif
+
/*
* ProcSignalShmemSize
* Compute space needed for ProcSignal's shared memory
@@ -176,6 +181,43 @@ ProcSignalInit(const uint8 *cancel_key, int cancel_key_len)
uint32 old_pss_pid;
Assert(cancel_key_len >= 0 && cancel_key_len <= MAX_CANCEL_KEY_LENGTH);
+
+#ifdef DEBUG_SHMEM_RESIZE
+ /*
+ * Introduced for debugging purposes. You can change the variable at
+ * runtime using gdb, then start new backends with delayed ProcSignal
+ * initialization. Simple pg_usleep wont work here due to SIGHUP interrupt
+ * needed for testing. Taken from pg_sleep;
+ */
+ if (delay_proc_signal_init)
+ {
+#define GetNowFloat() ((float8) GetCurrentTimestamp() / 1000000.0)
+ float8 endtime = GetNowFloat() + 5;
+
+ for (;;)
+ {
+ float8 delay;
+ long delay_ms;
+
+ CHECK_FOR_INTERRUPTS();
+
+ delay = endtime - GetNowFloat();
+ if (delay >= 600.0)
+ delay_ms = 600000;
+ else if (delay > 0.0)
+ delay_ms = (long) (delay * 1000.0);
+ else
+ break;
+
+ (void) WaitLatch(MyLatch,
+ WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+ delay_ms,
+ WAIT_EVENT_PG_SLEEP);
+ ResetLatch(MyLatch);
+ }
+ }
+#endif
+
if (MyProcNumber < 0)
elog(ERROR, "MyProcNumber not set");
if (MyProcNumber >= NumProcSignalSlots)
@@ -615,6 +657,10 @@ ProcessProcSignalBarrier(void)
case PROCSIGNAL_BARRIER_SMGRRELEASE:
processed = ProcessBarrierSmgrRelease();
break;
+ case PROCSIGNAL_BARRIER_SHMEM_RESIZE:
+ processed = ProcessBarrierShmemResize(
+ &ShmemCtrl->Barrier);
+ break;
}
/*
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 8d025f0e907..9fa277b91d7 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -498,17 +498,26 @@ ShmemInitStructInSegment(const char *name, Size size, bool *foundPtr,
{
/*
* Structure is in the shmem index so someone else has allocated it
- * already. The size better be the same as the size we are trying to
- * initialize to, or there is a name conflict (or worse).
+ * already. Verify the structure's size:
+ * - If it's the same, we've found the expected structure.
+ * - If it's different, we're resizing the expected structure.
+ *
+ * XXX: There is an implicit assumption this can only happen in
+ * "resizable" segments, where only one shared structure is allowed.
+ * This has to be implemented more cleanly.
*/
if (result->size != size)
{
- LWLockRelease(ShmemIndexLock);
- ereport(ERROR,
- (errmsg("ShmemIndex entry size is wrong for data structure"
- " \"%s\": expected %zu, actual %zu",
- name, size, result->size)));
+ Size delta = size - result->size;
+
+ result->size = size;
+
+ /* Reflect size change in the shared segment */
+ SpinLockAcquire(Segments[shmem_segment].ShmemLock);
+ Segments[shmem_segment].ShmemSegHdr->freeoffset += delta;
+ SpinLockRelease(Segments[shmem_segment].ShmemLock);
}
+
structPtr = result->location;
}
else
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 0d1b6466d1e..0942d2bffe2 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -62,6 +62,7 @@
#include "rewrite/rewriteHandler.h"
#include "storage/bufmgr.h"
#include "storage/ipc.h"
+#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
@@ -4309,6 +4310,15 @@ PostgresMain(const char *dbname, const char *username)
*/
BeginReportingGUCOptions();
+ /* Verify the shared barrier, if it's still active: join and wait. */
+ WaitOnShmemBarrier();
+
+ /*
+ * After waiting on the barrier above we guaranteed to have NSharedBuffers
+ * broadcasted, so we can use it in the function below.
+ */
+ AdjustShmemSize();
+
/*
* Also set up handler to log session end; we have to wait till now to be
* sure Log_disconnections has its final value.
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 4da68312b5f..691fa14e9e3 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -155,6 +155,8 @@ REPLICATION_ORIGIN_DROP "Waiting for a replication origin to become inactive so
REPLICATION_SLOT_DROP "Waiting for a replication slot to become inactive so it can be dropped."
RESTORE_COMMAND "Waiting for <xref linkend="guc-restore-command"/> to complete."
SAFE_SNAPSHOT "Waiting to obtain a valid snapshot for a <literal>READ ONLY DEFERRABLE</literal> transaction."
+SHMEM_RESIZE_START "Waiting for other backends to start resizing shared memory."
+SHMEM_RESIZE_DONE "Waiting for other backends to finish resizing shared memory."
SYNC_REP "Waiting for confirmation from a remote server during synchronous replication."
WAL_BUFFER_INIT "Waiting on WAL buffer to be initialized."
WAL_RECEIVER_EXIT "Waiting for the WAL receiver to exit."
@@ -352,6 +354,7 @@ DSMRegistry "Waiting to read or update the dynamic shared memory registry."
InjectionPoint "Waiting to read or update information related to injection points."
SerialControl "Waiting to read or update shared <filename>pg_serial</filename> state."
AioWorkerSubmissionQueue "Waiting to access AIO worker submission queue."
+ShmemResize "Waiting to resize shared memory."
#
# END OF PREDEFINED LWLOCKS (DO NOT CHANGE THIS LINE)
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index a221e446d6a..d8acec0f911 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2366,14 +2366,14 @@ struct config_int ConfigureNamesInt[] =
* checking for overflow, so we mustn't allow more than INT_MAX / 2.
*/
{
- {"shared_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+ {"shared_buffers", PGC_SIGHUP, RESOURCES_MEM,
gettext_noop("Sets the number of shared memory buffers used by the server."),
NULL,
GUC_UNIT_BLOCKS
},
&NBuffers,
16384, 16, INT_MAX / 2,
- NULL, NULL, NULL
+ NULL, assign_shared_buffers, NULL
},
{
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index edac9db6a12..4239ebe640b 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -317,7 +317,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
int32 *buffers_skipped);
/* in buf_init.c */
-extern void BufferManagerShmemInit(void);
+extern void BufferManagerShmemInit(int);
extern Size BufferManagerShmemSize(int);
/* in localbuf.c */
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 6ebda479ced..bb7ae4d33b3 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -64,6 +64,7 @@ typedef void (*shmem_startup_hook_type) (void);
/* ipc.c */
extern PGDLLIMPORT bool proc_exit_inprogress;
extern PGDLLIMPORT bool shmem_exit_inprogress;
+extern PGDLLIMPORT volatile bool pending_pm_shmem_resize;
pg_noreturn extern void proc_exit(int code);
extern void shmem_exit(int code);
@@ -83,5 +84,7 @@ extern void CreateSharedMemoryAndSemaphores(void);
extern void AttachSharedMemoryStructs(void);
#endif
extern void InitializeShmemGUCs(void);
+extern void CoordinateShmemResize(void);
+extern bool AnonymousShmemResize(void);
#endif /* IPC_H */
diff --git a/src/include/storage/lwlocklist.h b/src/include/storage/lwlocklist.h
index a9681738146..558da6fdd55 100644
--- a/src/include/storage/lwlocklist.h
+++ b/src/include/storage/lwlocklist.h
@@ -84,3 +84,4 @@ PG_LWLOCK(50, DSMRegistry)
PG_LWLOCK(51, InjectionPoint)
PG_LWLOCK(52, SerialControl)
PG_LWLOCK(53, AioWorkerSubmissionQueue)
+PG_LWLOCK(54, ShmemResize)
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index a7b275b4db9..bccdd45b1f7 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -24,6 +24,7 @@
#ifndef PG_SHMEM_H
#define PG_SHMEM_H
+#include "storage/barrier.h"
#include "storage/dsm_impl.h"
#include "storage/spin.h"
@@ -56,6 +57,25 @@ typedef struct ShmemSegment
extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
+/*
+ * ShmemControl is shared between backends and helps to coordinate shared
+ * memory resize.
+ */
+typedef struct
+{
+ pg_atomic_uint32 NSharedBuffers;
+ Barrier Barrier;
+ pg_atomic_uint64 Generation;
+ bool Resizable;
+} ShmemControl;
+
+extern PGDLLIMPORT ShmemControl *ShmemCtrl;
+
+/* The phases for shared memory resizing, used by for ProcSignal barrier. */
+#define SHMEM_RESIZE_REQUESTED 0
+#define SHMEM_RESIZE_START 1
+#define SHMEM_RESIZE_DONE 2
+
/* GUC variables */
extern PGDLLIMPORT int shared_memory_type;
extern PGDLLIMPORT int huge_pages;
@@ -109,6 +129,12 @@ extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags,
int *memfd_flags);
void PrepareHugePages(void);
+bool ProcessBarrierShmemResize(Barrier *barrier);
+void assign_shared_buffers(int newval, void *extra, bool *pending);
+void AdjustShmemSize(void);
+extern void WaitOnShmemBarrier(void);
+extern void ShmemControlInit(void);
+
/*
* To be able to dynamically resize largest parts of the data stored in shared
* memory, we split it into multiple shared memory mappings segments. Each
diff --git a/src/include/storage/pmsignal.h b/src/include/storage/pmsignal.h
index 428aa3fd68a..1a55bf57a70 100644
--- a/src/include/storage/pmsignal.h
+++ b/src/include/storage/pmsignal.h
@@ -42,6 +42,7 @@ typedef enum
PMSIGNAL_START_WALRECEIVER, /* start a walreceiver */
PMSIGNAL_ADVANCE_STATE_MACHINE, /* advance postmaster's state machine */
PMSIGNAL_XLOG_IS_SHUTDOWN, /* ShutdownXLOG() completed */
+ PMSIGNAL_SHMEM_RESIZE, /* resize shared memory */
} PMSignalReason;
#define NUM_PMSIGNALS (PMSIGNAL_XLOG_IS_SHUTDOWN+1)
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 2733bbb8c5b..97033f84dce 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -54,6 +54,7 @@ typedef enum
typedef enum
{
PROCSIGNAL_BARRIER_SMGRRELEASE, /* ask smgr to close files */
+ PROCSIGNAL_BARRIER_SHMEM_RESIZE, /* ask backends to resize shared memory */
} ProcSignalBarrierType;
/*
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 32d6e718adc..36e25ea8cd6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2751,6 +2751,7 @@ ShellTypeInfo
ShippableCacheEntry
ShippableCacheKey
ShmemIndexEnt
+ShmemControl
ShutdownForeignScan_function
ShutdownInformation
ShutdownMode
--
2.49.0
[text/plain] v5-0008-Support-shrinking-shared-buffers.patch (14.0K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/9-v5-0008-Support-shrinking-shared-buffers.patch)
download | inline diff:
From 5e190dc84ce7078b6c680d18736e56be90cecdab Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Thu, 19 Jun 2025 17:38:29 +0200
Subject: [PATCH v5 08/10] Support shrinking shared buffers
When shrinking the shared buffers pool, each buffer in the area being
shrunk needs to be flushed if it's dirty so as not to loose the changes
to that buffer after shrinking. Also, each such buffer needs to be
removed from the buffer mapping table so that backends do not access it
after shrinking.
Buffer eviction requires a separate barrier phase for two reasons:
1. No other backend should map a new page to any of buffers being
evicted when eviction is in progress. So they wait while eviction is
in progress.
2. Since a pinned buffer has the pin recorded in the backend local
memory as well as the buffer descriptor (which is in shared memory),
eviction should not coincide with remapping the shared memory of a
backend. Otherwise we might loose consistency of local and shared
pinning records. Hence it needs to be carried out in
ProcessBarrierShmemResize() and not in AnonymousShmemResize() as
indicated by now removed comment.
If a buffer being evicted is pinned, we raise a FATAL error but this should
improve. There are multiple options 1. to wait for the pinned buffer to get
unpinned, 2. the backend is killed or it itself cancels the query or 3.
rollback the operation. Note that option 1 and 2 would require the pinning
related local and shared records to be accessed. But we need infrastructure to
do either of this right now.
Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 42 +++++---
src/backend/storage/buffer/buf_init.c | 8 +-
src/backend/storage/buffer/bufmgr.c | 95 +++++++++++++++++++
src/backend/storage/buffer/freelist.c | 68 +++++++++++++
.../utils/activity/wait_event_names.txt | 1 +
src/include/storage/buf_internals.h | 1 +
src/include/storage/bufmgr.h | 1 +
src/include/storage/pg_shmem.h | 1 +
8 files changed, 202 insertions(+), 15 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index b3c90d15d52..e612a83c9f0 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -1011,14 +1011,6 @@ AnonymousShmemResize(void)
*/
pending_pm_shmem_resize = false;
- /*
- * XXX: Currently only increasing of shared_buffers is supported. For
- * decreasing something similar has to be done, but buffer blocks with
- * data have to be drained first.
- */
- if(NBuffersOld > NBuffers)
- return false;
-
#ifndef MAP_HUGETLB
/* PrepareHugePages should have dealt with this case */
Assert(huge_pages != HUGE_PAGES_ON && !huge_pages_on);
@@ -1112,11 +1104,14 @@ AnonymousShmemResize(void)
* all the pointers are still valid, and we only need to update
* structures size in the ShmemIndex once -- any other backend
* will pick up this shared structure from the index.
- *
- * XXX: This is the right place for buffer eviction as well.
*/
BufferManagerShmemInit(NBuffersOld);
+ /*
+ * Wipe out the evictor PID so that it can be used for the next
+ * buffer resizing operation.
+ */
+ ShmemCtrl->evictor_pid = 0;
/* If all fine, broadcast the new value */
pg_atomic_write_u32(&ShmemCtrl->NSharedBuffers, NBuffers);
}
@@ -1169,11 +1164,31 @@ ProcessBarrierShmemResize(Barrier *barrier)
* XXX: If we need to be able to abort resizing, this has to be done later,
* after the SHMEM_RESIZE_DONE.
*/
- if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+
+ /*
+ * Evict extra buffers when shrinking shared buffers. We need to do this
+ * while the memory for extra buffers is still mapped i.e. before remapping
+ * the shared memory segments to a smaller memory area.
+ */
+ if (NBuffersOld > NBuffersPending)
{
- Assert(IsUnderPostmaster);
- SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
+ BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START);
+
+ /*
+ * TODO: If the buffer eviction fails for any reason, we should
+ * gracefully rollback the shared buffer resizing and try again. But the
+ * infrastructure to do so is not available right now. Hence just raise
+ * a FATAL so that the system restarts.
+ */
+ if (!EvictExtraBuffers(NBuffersPending, NBuffersOld))
+ elog(FATAL, "buffer eviction failed");
+
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_EVICT))
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
}
+ else
+ if (BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_START))
+ SendPostmasterSignal(PMSIGNAL_SHMEM_RESIZE);
AnonymousShmemResize();
@@ -1683,5 +1698,6 @@ ShmemControlInit(void)
/* shmem_resizable should be initialized by now */
ShmemCtrl->Resizable = shmem_resizable;
+ ShmemCtrl->evictor_pid = 0;
}
}
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 8c1ea623392..6f5743036a2 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -157,8 +157,12 @@ BufferManagerShmemInit(int FirstBufferToInit)
}
#endif
- /* Correct last entry of linked list */
- GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
+ /*
+ * Correct last entry of linked list, when initializing the buffers or when
+ * expanding the buffers.
+ */
+ if (FirstBufferToInit < NBuffers)
+ GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 667aa0c0c78..169a44dd9fc 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -57,6 +57,7 @@
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
+#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/read_stream.h"
#include "storage/smgr.h"
@@ -7453,3 +7454,97 @@ const PgAioHandleCallbacks aio_local_buffer_readv_cb = {
.complete_local = local_buffer_readv_complete,
.report = buffer_readv_report,
};
+
+/*
+ * When shrinking shared buffers pool, evict the buffers which will not be part
+ * of the shrunk buffer pool.
+ */
+bool
+EvictExtraBuffers(int newBufSize, int oldBufSize)
+{
+ bool result = true;
+
+ /*
+ * If the buffer being evicated is locked, this function will need to wait.
+ * This function should not be called from a Postmaster since it can not wait on a lock.
+ */
+ Assert(IsUnderPostmaster);
+
+ /*
+ * Let only one backend perform eviction. We could split the work across all
+ * the backends but that doesn't seem necessary.
+ *
+ * The first backend to acquire ShmemResizeLock, sets its own PID as the
+ * evictor PID for other backends to know that the eviction is in progress or
+ * has already been performed. The evictor backend releases the lock when it
+ * finishes eviction. While the eviction is in progress, backends other than
+ * evictor backend won't be able to take the lock. They won't perform
+ * eviction. A backend may acquire the lock after eviction has completed, but
+ * it will not perform eviction since the evictor PID is already set. Evictor
+ * PID is reset only when the buffer resizing finishes. Thus only one backend
+ * will perform eviction in a given instance of shared buffers resizing.
+ *
+ * Any backend which acquires this lock will release it before the eviction
+ * phase finishes, hence the same lock can be reused for the next phase of
+ * resizing buffers.
+ */
+ if (LWLockConditionalAcquire(ShmemResizeLock, LW_EXCLUSIVE))
+ {
+ if (ShmemCtrl->evictor_pid == 0)
+ {
+ ShmemCtrl->evictor_pid = MyProcPid;
+
+ StrategyPurgeFreeList(newBufSize);
+
+ /*
+ * TODO: Before evicting any buffer, we should check whether any of the
+ * buffers are pinned. If we find that a buffer is pinned after evicting
+ * most of them, that will impact performance since all those evicted
+ * buffers might need to be read again.
+ */
+ for (Buffer buf = newBufSize + 1; buf <= oldBufSize; buf++)
+ {
+ BufferDesc *desc = GetBufferDescriptor(buf - 1);
+ uint32 buf_state;
+ bool buffer_flushed;
+
+ buf_state = pg_atomic_read_u32(&desc->state);
+
+ /*
+ * Nobody is expected to touch the buffers while resizing is
+ * going one hence unlocked precheck should be safe and saves
+ * some cycles.
+ */
+ if (!(buf_state & BM_VALID))
+ continue;
+
+ /*
+ * XXX: Looks like CurrentResourceOwner can be NULL here, find
+ * another one in that case?
+ * */
+ if (CurrentResourceOwner)
+ ResourceOwnerEnlarge(CurrentResourceOwner);
+
+ ReservePrivateRefCountEntry();
+
+ LockBufHdr(desc);
+
+ /*
+ * Now that we have locked buffer descriptor, make sure that the
+ * buffer without valid data has been skipped above.
+ */
+ Assert(buf_state & BM_VALID);
+
+ if (!EvictUnpinnedBufferInternal(desc, &buffer_flushed))
+ {
+ elog(WARNING, "could not remove buffer %u, it is pinned", buf);
+ result = false;
+ break;
+ }
+ }
+ }
+ LWLockRelease(ShmemResizeLock);
+ }
+
+ return result;
+}
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index bd390f2709d..7b9ed010e2f 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -527,6 +527,74 @@ StrategyInitialize(bool init)
}
+/*
+ * StrategyPurgeFreeList -- remove all buffers with id higher than the number of
+ * buffers in the buffer pool.
+ *
+ * This is called before evicting buffers while shrinking shared buffers, so that
+ * the free list does not reference a buffer that will be removed.
+ *
+ * The function is called after resizing has started and thus nobody should be
+ * traversing the free list and also not touching the buffers.
+ */
+void
+StrategyPurgeFreeList(int numBuffers)
+{
+ int firstBuffer = FREENEXT_END_OF_LIST;
+ int nextFree = StrategyControl->firstFreeBuffer;
+ BufferDesc *prevValidBuf = NULL;
+
+ SpinLockAcquire(&StrategyControl->buffer_strategy_lock);
+
+ while (nextFree != FREENEXT_END_OF_LIST)
+ {
+ BufferDesc *buf = GetBufferDescriptor(nextFree);
+
+ /* nextFree should be id of buffer being examined. */
+ Assert(nextFree == buf->buf_id);
+ /* The buffer should not be marked as not in the list. */
+ Assert(buf->freeNext != FREENEXT_NOT_IN_LIST);
+
+ /*
+ * If the buffer is within the new size of pool, keep it in the free list
+ * otherwise discard it.
+ */
+ if (buf->buf_id < numBuffers)
+ {
+ if (prevValidBuf != NULL)
+ prevValidBuf->freeNext = buf->buf_id;
+ prevValidBuf = buf;
+
+ /* Save the first free buffer in the list if not already known. */
+ if (firstBuffer == FREENEXT_NOT_IN_LIST)
+ firstBuffer = nextFree;
+ }
+ /* Examine the next buffer in the free list. */
+ nextFree = buf->freeNext;
+ }
+
+ /* Update the last valid free buffer, if there's any. */
+ if (prevValidBuf != NULL)
+ {
+ StrategyControl->lastFreeBuffer = prevValidBuf->buf_id;
+ prevValidBuf->freeNext = FREENEXT_END_OF_LIST;
+ }
+ else
+ StrategyControl->lastFreeBuffer = FREENEXT_END_OF_LIST;
+
+ /* Update first valid free buffer, if there's any. */
+ StrategyControl->firstFreeBuffer = firstBuffer;
+
+ SpinLockRelease(&StrategyControl->buffer_strategy_lock);
+
+ /*
+ * TODO: following was suggested by AI. Check whether it is required.
+ * If we removed all buffers from the freelist, reset the clock sweep
+ * pointer to zero. This is not strictly necessary, but it seems like a
+ * good idea to avoid confusion.
+ */
+}
+
/* ----------------------------------------------------------------
* Backend-private buffer ring management
* ----------------------------------------------------------------
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 691fa14e9e3..0c588b69a90 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -156,6 +156,7 @@ REPLICATION_SLOT_DROP "Waiting for a replication slot to become inactive so it c
RESTORE_COMMAND "Waiting for <xref linkend="guc-restore-command"/> to complete."
SAFE_SNAPSHOT "Waiting to obtain a valid snapshot for a <literal>READ ONLY DEFERRABLE</literal> transaction."
SHMEM_RESIZE_START "Waiting for other backends to start resizing shared memory."
+SHMEM_RESIZE_EVICT "Waiting for other backends to finish buffer evication phase."
SHMEM_RESIZE_DONE "Waiting for other backends to finish resizing shared memory."
SYNC_REP "Waiting for confirmation from a remote server during synchronous replication."
WAL_BUFFER_INIT "Waiting on WAL buffer to be initialized."
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 0dec7d93b3b..add15e3723b 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -453,6 +453,7 @@ extern void StrategyNotifyBgWriter(int bgwprocno);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);
+extern void StrategyPurgeFreeList(int numBuffers);
extern bool have_free_buffer(void);
/* buf_table.c */
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 4239ebe640b..0c554f0b130 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -315,6 +315,7 @@ extern void EvictRelUnpinnedBuffers(Relation rel,
int32 *buffers_evicted,
int32 *buffers_flushed,
int32 *buffers_skipped);
+extern bool EvictExtraBuffers(int fromBuf, int toBuf);
/* in buf_init.c */
extern void BufferManagerShmemInit(int);
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index bccdd45b1f7..9a3e68f76d8 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -64,6 +64,7 @@ extern PGDLLIMPORT ShmemSegment Segments[ANON_MAPPINGS];
typedef struct
{
pg_atomic_uint32 NSharedBuffers;
+ pid_t evictor_pid;
Barrier Barrier;
pg_atomic_uint64 Generation;
bool Resizable;
--
2.49.0
[text/plain] v5-0009-Reinitialize-StrategyControl-after-resizing-buffe.patch (16.8K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/10-v5-0009-Reinitialize-StrategyControl-after-resizing-buffe.patch)
download | inline diff:
From 475fffc314b4d5975faf94d43504f2dcc0f1dc8d Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Thu, 19 Jun 2025 17:38:51 +0200
Subject: [PATCH v5 09/10] Reinitialize StrategyControl after resizing buffers
... and BgBufferSync and ClockSweepTick adjustments
The commit introduces a separate function StrategyReInitialize() instead
of reusing StrategyInitialize() since some of the things that the second
one does are not required in the first one. Here's list of what
StrategyReInitialize() does and how does it differ from
StrategyInitialize().
1. When expanding the buffer pool add new buffers to the free list.
2. When shrinking buffers, we remove any buffers, in the area being
shrunk, from the freelist. While doing so we adjust the first and
last free buffer pointers in the StrategyControl area. Hence nothing
more needed after resizing.
3. Check the sanity of the free buffer list is added after resizing.
4. StrategyControl pointer needn't be fetched again since it should not
change. But added an Assert to make sure the pointer is valid.
5. &StrategyControl->buffer_strategy_lock need not be initialized again.
6. nextVictimBuffer, completePasses and numBufferAllocs are viewed in
the context of NBuffers. Now that NBuffers itself has changed, those
three do not make sense. Reset them as if the server has restarted
again.
This commit introduces a flag delay_shmem_resize, which postgresql
backends and workers can use to signal the coordinator to delay resizing
operation. Background writer sets this flag when its scanning buffers. Background
writer is blocked when the actual resizing is in progress. But if
resizing is about to begin, it does not scan the buffers by returning
from BgBufferSync(). It stops a scan in progress when it sees that the
resizing has begun. After the resizing is finished, it adjusts the
collected statistics according to the new size of the buffer pool at the
end of barrier processing.
Once the buffer resizing is finished, before resuming the regular
operation, bgwriter resets the information saved so far. This
information is viewed in the context of NBuffers and hence does not make
sense after NBuffer has changed.
Ashutosh Bapat
---
src/backend/port/sysv_shmem.c | 24 ++++-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/storage/buffer/buf_init.c | 11 ++-
src/backend/storage/buffer/bufmgr.c | 74 ++++++++++----
src/backend/storage/buffer/freelist.c | 133 ++++++++++++++++++++++++++
src/include/storage/buf_internals.h | 1 +
src/include/storage/bufmgr.h | 3 +-
src/include/storage/ipc.h | 1 +
8 files changed, 226 insertions(+), 23 deletions(-)
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index e612a83c9f0..e61a557966b 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -115,6 +115,7 @@ static AnonymousMapping Mappings[ANON_MAPPINGS];
/* Flag telling postmaster that resize is needed */
volatile bool pending_pm_shmem_resize = false;
+volatile bool delay_shmem_resize = false;
/* Keeps track of the previous NBuffers value */
static int NBuffersOld = -1;
@@ -1118,6 +1119,12 @@ AnonymousShmemResize(void)
LWLockRelease(ShmemResizeLock);
}
+
+ /*
+ * TODO: Shouldn't we call ResizeBufferPool() here as well? Or those
+ * backend who can not lock the LWLock conditionally won't resize the
+ * buffers.
+ */
}
return true;
@@ -1138,13 +1145,17 @@ ProcessBarrierShmemResize(Barrier *barrier)
{
Assert(IsUnderPostmaster);
- elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d",
- NBuffersOld, NBuffersPending, pending_pm_shmem_resize);
+ elog(DEBUG1, "Handle a barrier for shmem resizing from %d to %d, %d, %d",
+ NBuffersOld, NBuffersPending, pending_pm_shmem_resize, delay_shmem_resize);
/* Wait until we have seen the new NBuffers value */
if (!pending_pm_shmem_resize)
return false;
+ /* Wait till this process becomes ready to resize buffers. */
+ if (delay_shmem_resize)
+ return false;
+
/*
* First thing to do after attaching to the barrier is to wait for others.
* We can't simply use BarrierArriveAndWait, because backends might arrive
@@ -1195,6 +1206,15 @@ ProcessBarrierShmemResize(Barrier *barrier)
/* The second phase means the resize has finished, SHMEM_RESIZE_DONE */
BarrierArriveAndWait(barrier, WAIT_EVENT_SHMEM_RESIZE_DONE);
+ if (MyBackendType == B_BG_WRITER)
+ {
+ /*
+ * Before resuming regular background writer activity, adjust the
+ * statistics collected so far.
+ */
+ BgBufferSyncAdjust(NBuffersOld, NBuffers);
+ }
+
BarrierDetach(barrier);
return true;
}
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 72f5acceec7..32b34f28ead 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -233,7 +233,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
/*
* Do one cycle of dirty-buffer writing.
*/
- can_hibernate = BgBufferSync(&wb_context);
+ can_hibernate = BgBufferSync(&wb_context, false);
/* Report pending statistics to the cumulative stats system */
pgstat_report_bgwriter();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 6f5743036a2..62c1672fb70 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -164,8 +164,15 @@ BufferManagerShmemInit(int FirstBufferToInit)
if (FirstBufferToInit < NBuffers)
GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
- /* Init other shared buffer-management stuff */
- StrategyInitialize(!foundDescs);
+ /*
+ * Init other shared buffer-management stuff from scratch configuring buffer
+ * pool the first time. If we are just resizing buffer pool adjust only the
+ * required structures.
+ */
+ if (FirstBufferToInit == 0)
+ StrategyInitialize(!foundDescs);
+ else
+ StrategyReInitialize(FirstBufferToInit);
/* Initialize per-backend file flush context */
WritebackContextInit(&BackendWritebackContext,
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 169a44dd9fc..590fc737da8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3611,6 +3611,32 @@ BufferSync(int flags)
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_scan);
}
+/*
+ * Information saved between BgBufferSync() calls so we can determine the
+ * strategy point's advance rate and avoid scanning already-cleaned buffers. The
+ * variables are global instead of static local so that BgBufferSyncAdjust() can
+ * adjust it when resizing shared buffers.
+ */
+static bool saved_info_valid = false;
+static int prev_strategy_buf_id;
+static uint32 prev_strategy_passes;
+static int next_to_clean;
+static uint32 next_passes;
+
+/* Moving averages of allocation rate and clean-buffer density */
+static float smoothed_alloc = 0;
+static float smoothed_density = 10.0;
+
+void
+BgBufferSyncAdjust(int NBuffersOld, int NBuffersNew)
+{
+ saved_info_valid = false;
+#ifdef BGW_DEBUG
+ elog(DEBUG2, "invalidated background writer status after resizing buffers from %d to %d",
+ NBuffersOld, NBuffersNew);
+#endif
+}
+
/*
* BgBufferSync -- Write out some dirty buffers in the pool.
*
@@ -3623,27 +3649,13 @@ BufferSync(int flags)
* bgwriter_lru_maxpages to 0.)
*/
bool
-BgBufferSync(WritebackContext *wb_context)
+BgBufferSync(WritebackContext *wb_context, bool reset)
{
/* info obtained from freelist.c */
int strategy_buf_id;
uint32 strategy_passes;
uint32 recent_alloc;
- /*
- * Information saved between calls so we can determine the strategy
- * point's advance rate and avoid scanning already-cleaned buffers.
- */
- static bool saved_info_valid = false;
- static int prev_strategy_buf_id;
- static uint32 prev_strategy_passes;
- static int next_to_clean;
- static uint32 next_passes;
-
- /* Moving averages of allocation rate and clean-buffer density */
- static float smoothed_alloc = 0;
- static float smoothed_density = 10.0;
-
/* Potentially these could be tunables, but for now, not */
float smoothing_samples = 16;
float scan_whole_pool_milliseconds = 120000.0;
@@ -3666,6 +3678,22 @@ BgBufferSync(WritebackContext *wb_context)
long new_strategy_delta;
uint32 new_recent_alloc;
+ /*
+ * If buffer pool is being shrunk the buffer being written out may not remain
+ * valid. If the buffer pool is being expanded, more buffers will become
+ * available without even this function writing out any. Hence wait till
+ * buffer resizing finishes i.e. go into hibernation mode.
+ */
+ if (pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) != NBuffers)
+ return true;
+
+ /*
+ * Resizing shared buffers while this function is performing an LRU scan on
+ * them may lead to wrong results. Indicate that the resizing should wait for
+ * the LRU scan to complete.
+ */
+ delay_shmem_resize = true;
+
/*
* Find out where the freelist clock sweep currently is, and how many
* buffer allocations have happened since our last call.
@@ -3842,8 +3870,17 @@ BgBufferSync(WritebackContext *wb_context)
num_written = 0;
reusable_buffers = reusable_buffers_est;
- /* Execute the LRU scan */
- while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)
+ /*
+ * Execute the LRU scan.
+ *
+ * If buffer pool is being shrunk, the buffer being written may not remain
+ * valid. If the buffer pool is being expanded, more buffers will become
+ * available without even this function writing any. Hence stop what we are doing. This
+ * also unblocks other processes that are waiting for buffer resizing to
+ * finish.
+ */
+ while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est &&
+ pg_atomic_read_u32(&ShmemCtrl->NSharedBuffers) == NBuffers)
{
int sync_state = SyncOneBuffer(next_to_clean, true,
wb_context);
@@ -3902,6 +3939,9 @@ BgBufferSync(WritebackContext *wb_context)
#endif
}
+ /* Let the resizing commence. */
+ delay_shmem_resize = false;
+
/* Return true if OK to hibernate */
return (bufs_to_lap == 0 && recent_alloc == 0);
}
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 7b9ed010e2f..41641bb3ae6 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -98,6 +98,9 @@ static BufferDesc *GetBufferFromRing(BufferAccessStrategy strategy,
uint32 *buf_state);
static void AddBufferToRing(BufferAccessStrategy strategy,
BufferDesc *buf);
+#ifdef USE_ASSERT_CHECKING
+static void StrategyValidateFreeList(void);
+#endif /* USE_ASSERT_CHECKING */
/*
* ClockSweepTick - Helper routine for StrategyGetBuffer()
@@ -526,6 +529,88 @@ StrategyInitialize(bool init)
Assert(!init);
}
+/*
+ * StrategyReInitialize -- re-initialize the buffer cache replacement
+ * strategy.
+ *
+ * To be called when resizing buffer manager and only from the coordinator.
+ * TODO: Assess the differences between this function and StrategyInitialize().
+ */
+void
+StrategyReInitialize(int FirstBufferIdToInit)
+{
+ bool found;
+
+ /*
+ * Resizing memory for buffer pools should not affect the address of
+ * StrategyControl.
+ */
+ if (StrategyControl != (BufferStrategyControl *)
+ ShmemInitStructInSegment("Buffer Strategy Status",
+ sizeof(BufferStrategyControl),
+ &found, STRATEGY_SHMEM_SEGMENT))
+ elog(FATAL, "something went wrong while re-initializing the buffer strategy");
+
+ Assert(found);
+
+ /* TODO: Buffer lookup table adjustment: There are two options:
+ *
+ * 1. Resize the buffer lookup table to match the new number of buffers. But
+ * this requires rehashing all the entries in the buffer lookup table with
+ * the new table size.
+ *
+ * 2. Allocate maximum size of the buffer lookup table at the beginning and
+ * never resize it. This leaves sparse buffer lookup table which is
+ * inefficient from both memory and time perspective. According to David
+ * Rowley, the sparse entries in the buffer look up table cause frequent
+ * cacheline reload which affect performance. If the impact of that
+ * inefficiency in a benchmark is significant, we will need to consider first
+ * option.
+ */
+
+ /*
+ * When shrinking buffers, we must have adjusted the first and the last free
+ * buffer when removing the buffers being shrunk from the free list. Nothing
+ * to be done here.
+ *
+ * When expanding the shared buffers, new buffers are added at the end of the
+ * freelist or they form the new free list if there are no free buffers.
+ */
+ if (FirstBufferIdToInit < NBuffers)
+ {
+ if (StrategyControl->firstFreeBuffer == FREENEXT_END_OF_LIST)
+ StrategyControl->firstFreeBuffer = FirstBufferIdToInit;
+ else
+ {
+ Assert(StrategyControl->lastFreeBuffer >= 0);
+ GetBufferDescriptor(StrategyControl->lastFreeBuffer - 1)->freeNext = FirstBufferIdToInit;
+ }
+
+ StrategyControl->lastFreeBuffer = NBuffers - 1;
+ }
+
+ /* Check free list sanity after resizing. */
+#ifdef USE_ASSERT_CHECKING
+ StrategyValidateFreeList();
+#endif /* USE_ASSERT_CHECKING */
+
+ /*
+ * The clock sweep tick pointer might have got invalidated. Reset it as if
+ * starting a fresh server.
+ */
+ pg_atomic_write_u32(&StrategyControl->nextVictimBuffer, 0);
+
+ /*
+ * The old statistics is viewed in the context of the number of shared
+ * buffers. It does not make sense now that the number of shared buffers
+ * itself has changed.
+ */
+ StrategyControl->completePasses = 0;
+ pg_atomic_init_u32(&StrategyControl->numBufferAllocs, 0);
+
+ /* No pending notification */
+ StrategyControl->bgwprocno = -1;
+}
/*
* StrategyPurgeFreeList -- remove all buffers with id higher than the number of
@@ -595,6 +680,54 @@ StrategyPurgeFreeList(int numBuffers)
*/
}
+#ifdef USE_ASSERT_CHECKING
+/*
+ * StrategyValidateFreeList-- check sanity of free buffer list.
+ */
+static void
+StrategyValidateFreeList(void)
+{
+ int nextFree = StrategyControl->firstFreeBuffer;
+ int numFreeBuffers = 0;
+ int lastFreeBuffer = FREENEXT_END_OF_LIST;
+
+ SpinLockAcquire(&StrategyControl->buffer_strategy_lock);
+
+ while (nextFree != FREENEXT_END_OF_LIST)
+ {
+ BufferDesc *buf = GetBufferDescriptor(nextFree);
+
+ /* nextFree should be id of buffer being examined. */
+ Assert(nextFree == buf->buf_id);
+ Assert(buf->buf_id < NBuffers);
+ /* The buffer should not be marked as not in the list. */
+ Assert(buf->freeNext != FREENEXT_NOT_IN_LIST);
+
+ /* Update our knowledge of last buffer in the free list. */
+ lastFreeBuffer = buf->buf_id;
+
+ numFreeBuffers++;
+
+ /* Avoid infinite recursion in case there are cycles in free list. */
+ if (numFreeBuffers > NBuffers)
+ break;
+
+ nextFree = buf->freeNext;
+ }
+
+ Assert(numFreeBuffers <= NBuffers);
+
+ /*
+ * Make sure that the StrategyControl's knowledge of last free buffer
+ * agrees with what's there in the free list.
+ */
+ if (StrategyControl->firstFreeBuffer != FREENEXT_END_OF_LIST)
+ Assert(StrategyControl->lastFreeBuffer == lastFreeBuffer);
+
+ SpinLockRelease(&StrategyControl->buffer_strategy_lock);
+}
+#endif /* USE_ASSERT_CHECKING */
+
/* ----------------------------------------------------------------
* Backend-private buffer ring management
* ----------------------------------------------------------------
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index add15e3723b..46949e9d90e 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -454,6 +454,7 @@ extern void StrategyNotifyBgWriter(int bgwprocno);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);
extern void StrategyPurgeFreeList(int numBuffers);
+extern void StrategyReInitialize(int FirstBufferToInit);
extern bool have_free_buffer(void);
/* buf_table.c */
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 0c554f0b130..83a75eab844 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -298,7 +298,8 @@ extern bool ConditionalLockBufferForCleanup(Buffer buffer);
extern bool IsBufferCleanupOK(Buffer buffer);
extern bool HoldingBufferPinThatDelaysRecovery(void);
-extern bool BgBufferSync(struct WritebackContext *wb_context);
+extern bool BgBufferSync(struct WritebackContext *wb_context, bool reset);
+extern void BgBufferSyncAdjust(int NBuffersOld, int NBuffersNew);
extern uint32 GetPinLimit(void);
extern uint32 GetLocalPinLimit(void);
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index bb7ae4d33b3..7d1c64a9267 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -65,6 +65,7 @@ typedef void (*shmem_startup_hook_type) (void);
extern PGDLLIMPORT bool proc_exit_inprogress;
extern PGDLLIMPORT bool shmem_exit_inprogress;
extern PGDLLIMPORT volatile bool pending_pm_shmem_resize;
+extern PGDLLIMPORT volatile bool delay_shmem_resize;
pg_noreturn extern void proc_exit(int code);
extern void shmem_exit(int code);
--
2.49.0
[text/plain] v5-0010-Additional-validation-for-buffer-in-the-ring.patch (2.1K, ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/11-v5-0010-Additional-validation-for-buffer-in-the-ring.patch)
download | inline diff:
From 25816411c7a77a87b8527a901633865f1c1056b7 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Wed, 11 Jun 2025 18:15:06 +0530
Subject: [PATCH v5 10/10] Additional validation for buffer in the ring
If the buffer pool has been shrunk, the buffers in the buffer list may
not be valid anymore. Modify GetBufferFromRing to check if the buffer is
still valid before using it. This makes GetBufferFromRing() a bit more
expensive because of additional boolean condition. That may not be
expensive enough to affect query performance. The alternative to that is
more complex as explained below.
The strategy object is created in CurrentMemoryContext and is not
available in any global structure thus accessible when processing buffer
resizing barriers. We may modify GetAccessStrategy() to register
strategy in a global linked list and then arrange to deregister it once
it's no more in use. Looking at the places which use
GetAccessStrategy(), fixing all those may be some work.
Ashutosh Bapat
---
src/backend/storage/buffer/freelist.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 41641bb3ae6..74d070733a4 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -948,12 +948,13 @@ GetBufferFromRing(BufferAccessStrategy strategy, uint32 *buf_state)
strategy->current = 0;
/*
- * If the slot hasn't been filled yet, tell the caller to allocate a new
- * buffer with the normal allocation strategy. He will then fill this
- * slot by calling AddBufferToRing with the new buffer.
+ * If the slot hasn't been filled yet or the buffer in the slot has been
+ * invalidated when buffer pool was shrunk, tell the caller to allocate a new
+ * buffer with the normal allocation strategy. He will then fill this slot
+ * by calling AddBufferToRing with the new buffer.
*/
bufnum = strategy->buffers[strategy->current];
- if (bufnum == InvalidBuffer)
+ if (bufnum == InvalidBuffer || bufnum > NBuffers)
return NULL;
/*
--
2.49.0
view thread (167+ messages) latest in thread
Message-ID: <my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2>
Permalink: ../my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2/
Also on: postgresql.org/message-id/my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: 9erthalion6@gmail.com, ashutosh.bapat.oss@gmail.com, thomas.munro@gmail.com, Jack.Ng@huawei.com, jakkuniku@gmail.com
Subject: Re: Changing shared_buffers without restart
In-Reply-To: <my4hukmejato53ef465ev7lk3sqiqvneh7436rz64wmtc7rbfj@hmuxsf2ngov2>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox