Hi,
On Wed, Jan 15, 2025 at 03:11:32PM +0900, Michael Paquier wrote:
> On Fri, Jan 10, 2025 at 09:40:38AM +0000, Bertrand Drouvot wrote:
> > Please find attached v4 taking into account 2c14037bb5.
>
> +} PgStat_WalCounters;
> +
> +typedef struct PgStat_WalStats
> +{
> + PgStat_WalCounters wal_counters;
>
> I know that's a nit, but perhaps that could be a patch of its own,
> pushing that to pg_stat_wal_build_tuple() to reduce the diffs in the
> main patch.
Done in 0003 attached.
> - * Find or create a local PgStat_BackendPending entry for proc number.
> + * Find or create a local PgStat_BackendPendingIO entry for proc number.
>
> Seems like you are undoing a change here.
Arf, nice catch, hopefully that's only the comment.. Fixed in the attached.
> + * WAL pending statistics are incremented inside a critical section
> + * (see XLogWrite()), so we can't use pgstat_prep_pending_entry() and we
> rely on
> + * PendingBackendWalStats instead.
> + */
> +extern PGDLLIMPORT PgStat_PendingWalStats PendingBackendWalStats;
>
> Hmm. This makes me wonder if we should rethink a bit the way pending
> entries are retrieved and if we should do it beforehand for the WAL
> paths to avoid allocations in some critical sections. Isn't that also
> because we avoid calling pgstat_prep_backend_pending() for the I/O
> case as only backends are supported now, discarding cases like the
> checkpointer where I/O could happen in a critical path? As a whole,
> the approach taken by the patch is not really consistent with the
> rest.
I agree that's better to have a generic solution and to be consistent with
the other variable-numbered stats.
The attached is implementing in 0001 the proposition done in [1], i.e:
1. It adds a new allow_critical_section to PgStat_KindInfo for pgstats kinds
2. It ensures to set temporarly allowInCritSection to true when needed
Note that for safety reason 0001 does set allowInCritSection back to false
unconditionally (means not checking again for allow_critical_section).
While it avoids the failed assertion mentioned above and in [1] (on
the MemoryContextAllocZero() call), the TAP tests are still failing with a new
failed assertion.
If you apply the whole patch series attached, you'll see that:
make -C src/bin/pg_rewind check PROVE_TESTS=t/001_basic.pl
is failing with something like:
TRAP: failed Assert("CritSectionCount == 0"), File: "mcxt.c", Line: 1107, PID:
3295726
pg18/bin/postgres(ExceptionalCondition+0xbb)[0x59668bee1f6d]
pg18/bin/postgres(MemoryContextCreate+0x46)[0x59668bf2a8fe]
pg18/bin/postgres(AllocSetContextCreateInternal+0x1df)[0x59668bf1bb11]
pg18/bin/postgres(pgstat_prep_pending_entry+0x86)[0x59668bcff8cc]
pg18/bin/postgres(pgstat_prep_backend_pending+0x2b)[0x59668bd024a9]
This one is more problematic because we are in MemoryContextCreate() so that the
"workaround" above does not help. I need to put more thoughts on it but already
sharing the issue here (as also discussed in [1]).
[1]: https://www.postgresql.org/message-id/Z4d_eggsxtBEdJAG%40paquier.xyz
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
>From 327160f7f96bcdc1c3779d25bb0228f25a4c2504 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Thu, 16 Jan 2025 08:51:09 +0000
Subject: [PATCH v5 1/4] Add allow_critical_section to PgStat_KindInfo for
pgstats kinds
This new field controls if a variable-numbered stats kind is allowed
to allocate memory in contexts while in a critical section.
Allocating memory in contexts while in a critical section isn't usually allowed,
but we make an exception.
It means that there's a theoretical possibility to run out of memory while
allocating the memory, which leads to a PANIC.
The memory allocation here are small (pending entries or entry reference) so
that's unlikely to happen in practice.
This is useful for a following commit that will track WAL statistics while in
a critical section (while in XLogWrite() for example).
---
src/backend/utils/activity/pgstat.c | 19 +++++++++++++++++++
src/backend/utils/activity/pgstat_shmem.c | 13 +++++++++++++
src/include/utils/pgstat_internal.h | 3 +++
.../injection_points/injection_stats.c | 1 +
4 files changed, 36 insertions(+)
89.9% src/backend/utils/activity/
7.6% src/include/utils/
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index 34520535d54..a942e04bb97 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -284,6 +284,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .allow_critical_section = false,
/* so pg_stat_database entries can be seen in all databases */
.accessed_across_databases = true,
@@ -301,6 +302,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .allow_critical_section = false,
.shared_size = sizeof(PgStatShared_Relation),
.shared_data_off = offsetof(PgStatShared_Relation, stats),
@@ -316,6 +318,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .allow_critical_section = false,
.shared_size = sizeof(PgStatShared_Function),
.shared_data_off = offsetof(PgStatShared_Function, stats),
@@ -330,6 +333,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .allow_critical_section = false,
.accessed_across_databases = true,
@@ -347,6 +351,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .allow_critical_section = false,
/* so pg_stat_subscription_stats entries can be seen in all databases */
.accessed_across_databases = true,
@@ -364,6 +369,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = false,
+ .allow_critical_section = false,
.accessed_across_databases = true,
@@ -1316,7 +1322,20 @@ pgstat_prep_pending_entry(PgStat_Kind kind, Oid dboid, uint64 objid, bool *creat
Assert(entrysize != (size_t) -1);
+ /*
+ * That could be done within a critical section, which isn't usually
+ * allowed, but we make an exception. It means that there's a
+ * theoretical possibility that you run out of memory while preparing
+ * the entry, which leads to a PANIC. Fortunately the pending entry is
+ * small so that's unlikely to happen in practice.
+ */
+ if (pgstat_get_kind_info(kind)->allow_critical_section)
+ MemoryContextAllowInCriticalSection(pgStatPendingContext, true);
+
entry_ref->pending = MemoryContextAllocZero(pgStatPendingContext, entrysize);
+
+ MemoryContextAllowInCriticalSection(pgStatPendingContext, false);
+
dlist_push_tail(&pgStatPending, &entry_ref->pending_node);
}
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
index 342586397d6..cb1ad330bd4 100644
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -402,9 +402,22 @@ pgstat_get_entry_ref_cached(PgStat_HashKey key, PgStat_EntryRef **entry_ref_p)
{
PgStat_EntryRef *entry_ref;
+ /*
+ * That could be done within a critical section, which isn't usually
+ * allowed, but we make an exception. It means that there's a
+ * theoretical possibility that you run out of memory while creating
+ * the entry ref, which leads to a PANIC. Fortunately the pending
+ * entry is small so that's unlikely to happen in practice.
+ */
+ if (pgstat_get_kind_info(key.kind)->allow_critical_section)
+ MemoryContextAllowInCriticalSection(pgStatSharedRefContext, true);
+
cache_entry->entry_ref = entry_ref =
MemoryContextAlloc(pgStatSharedRefContext,
sizeof(PgStat_EntryRef));
+
+ MemoryContextAllowInCriticalSection(pgStatSharedRefContext, false);
+
entry_ref->shared_stats = NULL;
entry_ref->shared_entry = NULL;
entry_ref->pending = NULL;
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 4bb8e5c53ab..0b21603c863 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -216,6 +216,9 @@ typedef struct PgStat_KindInfo
/* Should stats be written to the on-disk stats file? */
bool write_to_file:1;
+ /* For variable-numbered stats: allow memory context in critical section */
+ bool allow_critical_section:1;
+
/*
* The size of an entry in the shared stats hash table (pointed to by
* PgStatShared_HashEntry->body). For fixed-numbered statistics, this is
diff --git a/src/test/modules/injection_points/injection_stats.c b/src/test/modules/injection_points/injection_stats.c
index 5db62bca66f..873dc88aace 100644
--- a/src/test/modules/injection_points/injection_stats.c
+++ b/src/test/modules/injection_points/injection_stats.c
@@ -40,6 +40,7 @@ static const PgStat_KindInfo injection_stats = {
.name = "injection_points",
.fixed_amount = false, /* Bounded by the number of points */
.write_to_file = true,
+ .allow_critical_section = false,
/* Injection points are system-wide */
.accessed_across_databases = true,
--
2.34.1
>From 0ff81e01d4292e575270a4bd380ebb0505c57e11 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Mon, 6 Jan 2025 07:51:27 +0000
Subject: [PATCH v5 2/4] Extract logic filling pg_stat_get_wal()'s tuple into
its own routine
This commit adds pg_stat_wal_build_tuple(), a helper routine for
pg_stat_get_wal(), that fills its tuple based on the contents
of PgStat_WalStats. This will be used in a follow-up commit that uses
the same structures as pg_stat_wal for reporting, but for the PGSTAT_KIND_BACKEND
statistics kind.
---
src/backend/utils/adt/pgstatfuncs.c | 56 ++++++++++++++++++-----------
1 file changed, 36 insertions(+), 20 deletions(-)
100.0% src/backend/utils/adt/
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0f5e0a9778d..0442be03304 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1604,20 +1604,22 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
}
/*
- * Returns statistics of WAL activity
+ * pg_stat_wal_build_tuple
+ *
+ * Helper routine for pg_stat_get_wal() returning one tuple based on the contents
+ * of wal_stats.
*/
-Datum
-pg_stat_get_wal(PG_FUNCTION_ARGS)
+static Datum
+pg_stat_wal_build_tuple(PgStat_WalStats wal_stats)
{
-#define PG_STAT_GET_WAL_COLS 9
+#define PG_STAT_WAL_COLS 9
TupleDesc tupdesc;
- Datum values[PG_STAT_GET_WAL_COLS] = {0};
- bool nulls[PG_STAT_GET_WAL_COLS] = {0};
+ Datum values[PG_STAT_WAL_COLS] = {0};
+ bool nulls[PG_STAT_WAL_COLS] = {0};
char buf[256];
- PgStat_WalStats *wal_stats;
/* Initialise attributes information in the tuple descriptor */
- tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_WAL_COLS);
+ tupdesc = CreateTemplateTupleDesc(PG_STAT_WAL_COLS);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "wal_records",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "wal_fpi",
@@ -1639,34 +1641,48 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
BlessTupleDesc(tupdesc);
- /* Get statistics about WAL activity */
- wal_stats = pgstat_fetch_stat_wal();
-
/* Fill values and NULLs */
- values[0] = Int64GetDatum(wal_stats->wal_records);
- values[1] = Int64GetDatum(wal_stats->wal_fpi);
+ values[0] = Int64GetDatum(wal_stats.wal_records);
+ values[1] = Int64GetDatum(wal_stats.wal_fpi);
/* Convert to numeric. */
- snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats->wal_bytes);
+ snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats.wal_bytes);
values[2] = DirectFunctionCall3(numeric_in,
CStringGetDatum(buf),
ObjectIdGetDatum(0),
Int32GetDatum(-1));
- values[3] = Int64GetDatum(wal_stats->wal_buffers_full);
- values[4] = Int64GetDatum(wal_stats->wal_write);
- values[5] = Int64GetDatum(wal_stats->wal_sync);
+ values[3] = Int64GetDatum(wal_stats.wal_buffers_full);
+ values[4] = Int64GetDatum(wal_stats.wal_write);
+ values[5] = Int64GetDatum(wal_stats.wal_sync);
/* Convert counters from microsec to millisec for display */
- values[6] = Float8GetDatum(((double) wal_stats->wal_write_time) / 1000.0);
- values[7] = Float8GetDatum(((double) wal_stats->wal_sync_time) / 1000.0);
+ values[6] = Float8GetDatum(((double) wal_stats.wal_write_time) / 1000.0);
+ values[7] = Float8GetDatum(((double) wal_stats.wal_sync_time) / 1000.0);
- values[8] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+ if (wal_stats.stat_reset_timestamp != 0)
+ values[8] = TimestampTzGetDatum(wal_stats.stat_reset_timestamp);
+ else
+ nulls[8] = true;
/* Returns the record as Datum */
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
+/*
+ * Returns statistics of WAL activity
+ */
+Datum
+pg_stat_get_wal(PG_FUNCTION_ARGS)
+{
+ PgStat_WalStats *wal_stats;
+
+ /* Get statistics about WAL activity */
+ wal_stats = pgstat_fetch_stat_wal();
+
+ return (pg_stat_wal_build_tuple(*wal_stats));
+}
+
/*
* Returns statistics of SLRU caches.
*/
--
2.34.1
>From 383d186b1699ac74a53f2fea85ced5abc10cd558 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Thu, 16 Jan 2025 15:06:01 +0000
Subject: [PATCH v5 3/4] Adding a new PgStat_WalCounters struct
This new struct contains only the counters related to the WAL statistics.
This will be used in a follow-up commit that uses the same structures but
for the PGSTAT_KIND_BACKEND statistics kind.
---
src/backend/utils/activity/pgstat_wal.c | 4 ++--
src/backend/utils/adt/pgstatfuncs.c | 28 +++++++++++++------------
src/include/pgstat.h | 7 ++++++-
src/tools/pgindent/typedefs.list | 1 +
4 files changed, 24 insertions(+), 16 deletions(-)
14.1% src/backend/utils/activity/
79.8% src/backend/utils/adt/
5.0% src/include/
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index 18fa6b2936a..bfc06178a68 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -117,9 +117,9 @@ pgstat_wal_flush_cb(bool nowait)
return true;
#define WALSTAT_ACC(fld, var_to_add) \
- (stats_shmem->stats.fld += var_to_add.fld)
+ (stats_shmem->stats.wal_counters.fld += var_to_add.fld)
#define WALSTAT_ACC_INSTR_TIME(fld) \
- (stats_shmem->stats.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
+ (stats_shmem->stats.wal_counters.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
WALSTAT_ACC(wal_records, wal_usage_diff);
WALSTAT_ACC(wal_fpi, wal_usage_diff);
WALSTAT_ACC(wal_bytes, wal_usage_diff);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0442be03304..97510d48eef 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1607,10 +1607,11 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
* pg_stat_wal_build_tuple
*
* Helper routine for pg_stat_get_wal() returning one tuple based on the contents
- * of wal_stats.
+ * of wal_counters.
*/
static Datum
-pg_stat_wal_build_tuple(PgStat_WalStats wal_stats)
+pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
+ TimestampTz stat_reset_timestamp)
{
#define PG_STAT_WAL_COLS 9
TupleDesc tupdesc;
@@ -1642,26 +1643,26 @@ pg_stat_wal_build_tuple(PgStat_WalStats wal_stats)
BlessTupleDesc(tupdesc);
/* Fill values and NULLs */
- values[0] = Int64GetDatum(wal_stats.wal_records);
- values[1] = Int64GetDatum(wal_stats.wal_fpi);
+ values[0] = Int64GetDatum(wal_counters.wal_records);
+ values[1] = Int64GetDatum(wal_counters.wal_fpi);
/* Convert to numeric. */
- snprintf(buf, sizeof buf, UINT64_FORMAT, wal_stats.wal_bytes);
+ snprintf(buf, sizeof buf, UINT64_FORMAT, wal_counters.wal_bytes);
values[2] = DirectFunctionCall3(numeric_in,
CStringGetDatum(buf),
ObjectIdGetDatum(0),
Int32GetDatum(-1));
- values[3] = Int64GetDatum(wal_stats.wal_buffers_full);
- values[4] = Int64GetDatum(wal_stats.wal_write);
- values[5] = Int64GetDatum(wal_stats.wal_sync);
+ values[3] = Int64GetDatum(wal_counters.wal_buffers_full);
+ values[4] = Int64GetDatum(wal_counters.wal_write);
+ values[5] = Int64GetDatum(wal_counters.wal_sync);
/* Convert counters from microsec to millisec for display */
- values[6] = Float8GetDatum(((double) wal_stats.wal_write_time) / 1000.0);
- values[7] = Float8GetDatum(((double) wal_stats.wal_sync_time) / 1000.0);
+ values[6] = Float8GetDatum(((double) wal_counters.wal_write_time) / 1000.0);
+ values[7] = Float8GetDatum(((double) wal_counters.wal_sync_time) / 1000.0);
- if (wal_stats.stat_reset_timestamp != 0)
- values[8] = TimestampTzGetDatum(wal_stats.stat_reset_timestamp);
+ if (stat_reset_timestamp != 0)
+ values[8] = TimestampTzGetDatum(stat_reset_timestamp);
else
nulls[8] = true;
@@ -1680,7 +1681,8 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
/* Get statistics about WAL activity */
wal_stats = pgstat_fetch_stat_wal();
- return (pg_stat_wal_build_tuple(*wal_stats));
+ return (pg_stat_wal_build_tuple(wal_stats->wal_counters,
+ wal_stats->stat_reset_timestamp));
}
/*
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index a878402f502..bb8e0044a47 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -463,7 +463,7 @@ typedef struct PgStat_StatTabEntry
PgStat_Counter autoanalyze_count;
} PgStat_StatTabEntry;
-typedef struct PgStat_WalStats
+typedef struct PgStat_WalCounters
{
PgStat_Counter wal_records;
PgStat_Counter wal_fpi;
@@ -473,6 +473,11 @@ typedef struct PgStat_WalStats
PgStat_Counter wal_sync;
PgStat_Counter wal_write_time;
PgStat_Counter wal_sync_time;
+} PgStat_WalCounters;
+
+typedef struct PgStat_WalStats
+{
+ PgStat_WalCounters wal_counters;
TimestampTz stat_reset_timestamp;
} PgStat_WalStats;
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 94dc956ae8c..d8b6623ba9c 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2176,6 +2176,7 @@ PgStat_SubXactStatus
PgStat_TableCounts
PgStat_TableStatus
PgStat_TableXactStatus
+PgStat_WalCounters
PgStat_WalStats
PgXmlErrorContext
PgXmlStrictness
--
2.34.1
>From 094bc124baea085a721f0013da290f3b92f96607 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Mon, 6 Jan 2025 10:00:00 +0000
Subject: [PATCH v5 4/4] per backend WAL statistics
Now that commit 9aea73fc61 added backend-level statistics to pgstats (and
per backend IO statistics) we can more easily add per backend statistics.
This commit adds per backend WAL statistics using the same layer as pg_stat_wal,
except that it is now possible to know how much WAL activity is happening in each
backend rather than an overall aggregate of all the activity. A function called
pg_stat_get_backend_wal() is added to access this data depending on the
PID of a backend.
Note that allow_critical_section has been enabled for the PGSTAT_KIND_BACKEND
stats kind as we are now tracking variable-numbered stats in critical section(s)
(XLogWrite() for example).
The same limitation as in 9aea73fc61 persists, meaning that Auxiliary processes
are not included in this set of statistics.
XXX: bump catalog version
---
doc/src/sgml/config.sgml | 4 +-
doc/src/sgml/monitoring.sgml | 19 +++++++
src/backend/access/transam/xlog.c | 44 +++++++++++++--
src/backend/utils/activity/pgstat.c | 2 +-
src/backend/utils/activity/pgstat_backend.c | 59 +++++++++++++++++++++
src/backend/utils/activity/pgstat_wal.c | 2 +
src/backend/utils/adt/pgstatfuncs.c | 53 +++++++++++++++++-
src/include/catalog/pg_proc.dat | 7 +++
src/include/pgstat.h | 43 ++++++++-------
src/include/utils/pgstat_internal.h | 3 +-
src/test/regress/expected/stats.out | 14 +++++
src/test/regress/sql/stats.sql | 6 +++
12 files changed, 227 insertions(+), 29 deletions(-)
14.2% doc/src/sgml/
14.9% src/backend/access/transam/
28.8% src/backend/utils/activity/
19.7% src/backend/utils/adt/
7.0% src/include/catalog/
5.1% src/include/
5.6% src/test/regress/expected/
4.3% src/test/regress/sql/
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3f41a17b1fe..075cb4fe1a8 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8292,7 +8292,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
measure the overhead of timing on your system.
I/O timing information is
displayed in <link linkend="monitoring-pg-stat-wal-view">
- <structname>pg_stat_wal</structname></link>.
+ <structname>pg_stat_wal</structname></link> and in the output of the
+ <link linkend="pg-stat-get-backend-wal">
+ <function>pg_stat_get_backend_wal()</function></link> function.
Only superusers and users with the appropriate <literal>SET</literal>
privilege can change this setting.
</para>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index e5888fae2b5..8fdf7d13f21 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -4824,6 +4824,25 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para></entry>
</row>
+ <row>
+ <entry id="pg-stat-get-backend-wal" role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_stat_get_backend_wal</primary>
+ </indexterm>
+ <function>pg_stat_get_backend_wal</function> ( <type>integer</type> )
+ <returnvalue>record</returnvalue>
+ </para>
+ <para>
+ Returns WAL statistics about the backend with the specified
+ process ID. The output fields are exactly the same as the ones in the
+ <structname>pg_stat_wal</structname> view.
+ </para>
+ <para>
+ The function does not return WAL statistics for the checkpointer,
+ the background writer, the startup process and the autovacuum launcher.
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index bf3dbda901d..d09a079bcbb 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -96,6 +96,7 @@
#include "utils/guc_hooks.h"
#include "utils/guc_tables.h"
#include "utils/injection_point.h"
+#include "utils/pgstat_internal.h"
#include "utils/ps_status.h"
#include "utils/relmapper.h"
#include "utils/snapmgr.h"
@@ -2058,6 +2059,15 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
XLogWrite(WriteRqst, tli, false);
LWLockRelease(WALWriteLock);
PendingWalStats.wal_buffers_full++;
+
+ if (pgstat_tracks_backend_bktype(MyBackendType))
+ {
+ PgStat_BackendPending *entry_ref;
+
+ entry_ref = pgstat_prep_backend_pending(MyProcNumber);
+ entry_ref->pending_wal.wal_buffers_full++;
+ }
+
TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
}
/* Re-acquire WALBufMappingLock and retry */
@@ -2426,11 +2436,14 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
Size nleft;
ssize_t written;
instr_time start;
+ instr_time end;
/* OK to write the page(s) */
from = XLogCtl->pages + startidx * (Size) XLOG_BLCKSZ;
nbytes = npages * (Size) XLOG_BLCKSZ;
nleft = nbytes;
+ /* keep compiler quiet */
+ INSTR_TIME_SET_ZERO(end);
do
{
errno = 0;
@@ -2451,14 +2464,24 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
*/
if (track_wal_io_timing)
{
- instr_time end;
-
INSTR_TIME_SET_CURRENT(end);
INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_write_time, end, start);
}
PendingWalStats.wal_write++;
+ if (pgstat_tracks_backend_bktype(MyBackendType))
+ {
+ PgStat_BackendPending *entry_ref;
+
+ entry_ref = pgstat_prep_backend_pending(MyProcNumber);
+ entry_ref->pending_wal.wal_write++;
+
+ if (track_wal_io_timing)
+ INSTR_TIME_ACCUM_DIFF(entry_ref->pending_wal.wal_write_time,
+ end, start);
+ }
+
if (written <= 0)
{
char xlogfname[MAXFNAMELEN];
@@ -8684,8 +8707,11 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
{
char *msg = NULL;
instr_time start;
+ instr_time end;
Assert(tli != 0);
+ /* keep compiler quiet */
+ INSTR_TIME_SET_ZERO(end);
/*
* Quick exit if fsync is disabled or write() has already synced the WAL
@@ -8751,13 +8777,23 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
*/
if (track_wal_io_timing)
{
- instr_time end;
-
INSTR_TIME_SET_CURRENT(end);
INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_sync_time, end, start);
}
PendingWalStats.wal_sync++;
+
+ if (pgstat_tracks_backend_bktype(MyBackendType))
+ {
+ PgStat_BackendPending *entry_ref;
+
+ entry_ref = pgstat_prep_backend_pending(MyProcNumber);
+ entry_ref->pending_wal.wal_sync++;
+
+ if (track_wal_io_timing)
+ INSTR_TIME_ACCUM_DIFF(entry_ref->pending_wal.wal_sync_time,
+ end, start);
+ }
}
/*
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index a942e04bb97..65b2f687816 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -369,7 +369,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = false,
- .allow_critical_section = false,
+ .allow_critical_section = true,
.accessed_across_databases = true,
diff --git a/src/backend/utils/activity/pgstat_backend.c b/src/backend/utils/activity/pgstat_backend.c
index 79e4d0a3053..94762b12f8d 100644
--- a/src/backend/utils/activity/pgstat_backend.c
+++ b/src/backend/utils/activity/pgstat_backend.c
@@ -24,6 +24,14 @@
#include "utils/pgstat_internal.h"
+/*
+ * WAL usage counters saved from pgWalUsage at the previous call to
+ * pgstat_report_wal(). This is used to calculate how much WAL usage
+ * happens between pgstat_report_wal() calls, by subtracting
+ * the previous counters from the current ones.
+ */
+static WalUsage prevBackendWalUsage;
+
/*
* Returns statistics of a backend by proc number.
*/
@@ -77,6 +85,52 @@ pgstat_flush_backend_entry_io(PgStat_EntryRef *entry_ref)
}
}
+/*
+ * Flush out locally pending backend WAL statistics. Locking is managed
+ * by the caller.
+ */
+static void
+pgstat_flush_backend_entry_wal(PgStat_EntryRef *entry_ref)
+{
+ PgStatShared_Backend *shbackendent;
+ PgStat_BackendPending *pendingent;
+ PgStat_WalCounters *bktype_shstats;
+ PgStat_PendingWalStats pending_wal;
+ WalUsage wal_usage_diff = {0};
+
+ shbackendent = (PgStatShared_Backend *) entry_ref->shared_stats;
+ pendingent = (PgStat_BackendPending *) entry_ref->pending;
+ bktype_shstats = &shbackendent->stats.wal_stats;
+ pending_wal = pendingent->pending_wal;
+
+ /*
+ * We don't update the WAL usage portion of the local WalStats elsewhere.
+ * Calculate how much WAL usage counters were increased by subtracting the
+ * previous counters from the current ones.
+ */
+ WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevBackendWalUsage);
+
+#define WALSTAT_ACC(fld, var_to_add) \
+ (bktype_shstats->fld += var_to_add.fld)
+#define WALSTAT_ACC_INSTR_TIME(fld) \
+ (bktype_shstats->fld += INSTR_TIME_GET_MICROSEC(pending_wal.fld))
+ WALSTAT_ACC(wal_buffers_full, pending_wal);
+ WALSTAT_ACC(wal_write, pending_wal);
+ WALSTAT_ACC(wal_sync, pending_wal);
+ WALSTAT_ACC(wal_records, wal_usage_diff);
+ WALSTAT_ACC(wal_fpi, wal_usage_diff);
+ WALSTAT_ACC(wal_bytes, wal_usage_diff);
+ WALSTAT_ACC_INSTR_TIME(wal_write_time);
+ WALSTAT_ACC_INSTR_TIME(wal_sync_time);
+#undef WALSTAT_ACC_INSTR_TIME
+#undef WALSTAT_ACC
+
+ /*
+ * Save the current counters for the subsequent calculation of WAL usage.
+ */
+ prevBackendWalUsage = pgWalUsage;
+}
+
/*
* Wrapper routine to flush backend statistics.
*/
@@ -94,6 +148,9 @@ pgstat_flush_backend_entry(PgStat_EntryRef *entry_ref, bool nowait,
if (flags & PGSTAT_BACKEND_FLUSH_IO)
pgstat_flush_backend_entry_io(entry_ref);
+ if (flags & PGSTAT_BACKEND_FLUSH_WAL)
+ pgstat_flush_backend_entry_wal(entry_ref);
+
pgstat_unlock_entry(entry_ref);
return true;
@@ -147,6 +204,8 @@ pgstat_create_backend(ProcNumber procnum)
* e.g. if we previously used this proc number.
*/
memset(&shstatent->stats, 0, sizeof(shstatent->stats));
+
+ prevBackendWalUsage = pgWalUsage;
}
/*
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index bfc06178a68..33627642261 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -55,6 +55,8 @@ pgstat_report_wal(bool force)
/* flush wal stats */
pgstat_flush_wal(nowait);
+ pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_WAL);
+
/* flush IO stats */
pgstat_flush_io(nowait);
}
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 97510d48eef..52bfda4f923 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1606,8 +1606,8 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
/*
* pg_stat_wal_build_tuple
*
- * Helper routine for pg_stat_get_wal() returning one tuple based on the contents
- * of wal_counters.
+ * Helper routine for pg_stat_get_wal() and pg_stat_get_backend_wal () returning
+ * one tuple based on the contents of wal_counters.
*/
static Datum
pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
@@ -1670,6 +1670,55 @@ pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
+/*
+ * Returns WAL statistics for a backend with given PID.
+ */
+Datum
+pg_stat_get_backend_wal(PG_FUNCTION_ARGS)
+{
+ int pid;
+ PGPROC *proc;
+ ProcNumber procNumber;
+ PgStat_Backend *backend_stats;
+ PgStat_WalCounters bktype_stats;
+ PgBackendStatus *beentry;
+
+ pid = PG_GETARG_INT32(0);
+ proc = BackendPidGetProc(pid);
+
+ /*
+ * This could be an auxiliary process but these do not report backend
+ * statistics due to pgstat_tracks_backend_bktype(), so there is no need
+ * for an extra call to AuxiliaryPidGetProc().
+ */
+ if (!proc)
+ PG_RETURN_NULL();
+
+ procNumber = GetNumberFromPGProc(proc);
+
+ beentry = pgstat_get_beentry_by_proc_number(procNumber);
+ if (!beentry)
+ PG_RETURN_NULL();
+
+ backend_stats = pgstat_fetch_stat_backend(procNumber);
+ if (!backend_stats)
+ PG_RETURN_NULL();
+
+ /* if PID does not match, leave */
+ if (beentry->st_procpid != pid)
+ PG_RETURN_NULL();
+
+ /* backend may be gone, so recheck in case */
+ if (beentry->st_backendType == B_INVALID)
+ PG_RETURN_NULL();
+
+ bktype_stats = backend_stats->wal_stats;
+
+ /* save tuples with data from this PgStat_BktypeIO */
+ return (pg_stat_wal_build_tuple(bktype_stats, backend_stats->stat_reset_timestamp));
+}
+
+
/*
* Returns statistics of WAL activity
*/
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index ba02ba53b29..9d57c69c152 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5929,6 +5929,13 @@
proargmodes => '{o,o,o,o,o,o,o,o,o}',
proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,wal_write,wal_sync,wal_write_time,wal_sync_time,stats_reset}',
prosrc => 'pg_stat_get_wal' },
+{ oid => '8037', descr => 'statistics: backend WAL activity',
+ proname => 'pg_stat_get_backend_wal', provolatile => 'v',
+ proparallel => 'r', prorettype => 'record', proargtypes => 'int4',
+ proallargtypes => '{int4,int8,int8,numeric,int8,int8,int8,float8,float8,timestamptz}',
+ proargmodes => '{i,o,o,o,o,o,o,o,o,o}',
+ proargnames => '{backend_pid,wal_records,wal_fpi,wal_bytes,wal_buffers_full,wal_write,wal_sync,wal_write_time,wal_sync_time,stats_reset}',
+ prosrc => 'pg_stat_get_backend_wal' },
{ oid => '6248', descr => 'statistics: information about WAL prefetching',
proname => 'pg_stat_get_recovery_prefetch', prorows => '1', proretset => 't',
provolatile => 'v', prorettype => 'record', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index bb8e0044a47..821104047a0 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -334,24 +334,6 @@ typedef struct PgStat_IO
PgStat_BktypeIO stats[BACKEND_NUM_TYPES];
} PgStat_IO;
-typedef struct PgStat_Backend
-{
- TimestampTz stat_reset_timestamp;
- PgStat_BktypeIO io_stats;
-} PgStat_Backend;
-
-/* ---------
- * PgStat_BackendPending Non-flushed backend stats.
- * ---------
- */
-typedef struct PgStat_BackendPending
-{
- /*
- * Backend statistics store the same amount of IO data as PGSTAT_KIND_IO.
- */
- PgStat_PendingIO pending_io;
-} PgStat_BackendPending;
-
typedef struct PgStat_StatDBEntry
{
PgStat_Counter xact_commit;
@@ -496,6 +478,29 @@ typedef struct PgStat_PendingWalStats
instr_time wal_sync_time;
} PgStat_PendingWalStats;
+/* ---------
+ * PgStat_BackendPending Non-flushed backend stats.
+ * ---------
+ */
+typedef struct PgStat_BackendPending
+{
+ /*
+ * Backend statistics store the same amount of IO data as PGSTAT_KIND_IO.
+ */
+ PgStat_PendingIO pending_io;
+
+ /*
+ * Backend statistics store the same amount of IO data as PGSTAT_KIND_WAL.
+ */
+ PgStat_PendingWalStats pending_wal;
+} PgStat_BackendPending;
+
+typedef struct PgStat_Backend
+{
+ TimestampTz stat_reset_timestamp;
+ PgStat_BktypeIO io_stats;
+ PgStat_WalCounters wal_stats;
+} PgStat_Backend;
/*
* Functions in pgstat.c
@@ -826,6 +831,4 @@ extern PGDLLIMPORT SessionEndType pgStatSessionEndCause;
/* updated directly by backends and background processes */
extern PGDLLIMPORT PgStat_PendingWalStats PendingWalStats;
-
-
#endif /* PGSTAT_H */
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 0b21603c863..5a284d8c94a 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -618,7 +618,8 @@ extern void pgstat_archiver_snapshot_cb(void);
/* flags for pgstat_flush_backend() */
#define PGSTAT_BACKEND_FLUSH_IO (1 << 0) /* Flush I/O statistics */
-#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO)
+#define PGSTAT_BACKEND_FLUSH_WAL (1 << 1) /* Flush WAL statistics */
+#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO | PGSTAT_BACKEND_FLUSH_WAL)
extern void pgstat_flush_backend(bool nowait, bits32 flags);
extern PgStat_BackendPending *pgstat_prep_backend_pending(ProcNumber procnum);
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index a0317b7208e..cc01fdf2741 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -832,6 +832,8 @@ SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELEC
SELECT num_requested AS rqst_ckpts_before FROM pg_stat_checkpointer \gset
-- Test pg_stat_wal (and make a temp table so our temp schema exists)
SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
+-- Test pg_stat_get_backend_wal (and make a temp table so our temp schema exists)
+SELECT wal_bytes AS backend_wal_bytes_before from pg_stat_get_backend_wal(pg_backend_pid()) \gset
CREATE TEMP TABLE test_stats_temp AS SELECT 17;
DROP TABLE test_stats_temp;
-- Checkpoint twice: The checkpointer reports stats after reporting completion
@@ -851,6 +853,18 @@ SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
t
(1 row)
+SELECT pg_stat_force_next_flush();
+ pg_stat_force_next_flush
+--------------------------
+
+(1 row)
+
+SELECT wal_bytes > :backend_wal_bytes_before FROM pg_stat_get_backend_wal(pg_backend_pid());
+ ?column?
+----------
+ t
+(1 row)
+
-- Test pg_stat_get_backend_idset() and some allied functions.
-- In particular, verify that their notion of backend ID matches
-- our temp schema index.
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 399c72bbcf7..28fe0a1a7d0 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -423,6 +423,9 @@ SELECT num_requested AS rqst_ckpts_before FROM pg_stat_checkpointer \gset
-- Test pg_stat_wal (and make a temp table so our temp schema exists)
SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
+-- Test pg_stat_get_backend_wal (and make a temp table so our temp schema exists)
+SELECT wal_bytes AS backend_wal_bytes_before from pg_stat_get_backend_wal(pg_backend_pid()) \gset
+
CREATE TEMP TABLE test_stats_temp AS SELECT 17;
DROP TABLE test_stats_temp;
@@ -435,6 +438,9 @@ CHECKPOINT;
SELECT num_requested > :rqst_ckpts_before FROM pg_stat_checkpointer;
SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
+SELECT pg_stat_force_next_flush();
+SELECT wal_bytes > :backend_wal_bytes_before FROM pg_stat_get_backend_wal(pg_backend_pid());
+
-- Test pg_stat_get_backend_idset() and some allied functions.
-- In particular, verify that their notion of backend ID matches
-- our temp schema index.
--
2.34.1
