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Add mem_exceeded_count column to pg_stat_replication_slots.

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This commit introduces a new column mem_exceeded_count to the
pg_stat_replication_slots view. This counter tracks how often the
memory used by logical decoding exceeds the logical_decoding_work_mem
limit. The new statistic helps users determine whether exceeding the
logical_decoding_work_mem limit is a rare occurrences or a frequent
issue, information that wasn't available through existing statistics.

Bumps catversion.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/978D21E8-9D3B-40EA-A4B1-F87BABE7868C@yesql.se
This commit is contained in:
Masahiko Sawada
2025-10-08 10:05:04 -07:00
parent 14ad0d7bf2
commit d3b6183dd9
13 changed files with 113 additions and 60 deletions
Download Patch File Download Diff File Expand all files Collapse all files

71
contrib/test_decoding/expected/stats.out
View File

@@ -37,12 +37,12 @@ SELECT pg_stat_force_next_flush();
(1 row)
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes
------------------------+------------+-------------+------------+-------------
regression_slot_stats1 | t | t | t | t
regression_slot_stats2 | t | t | t | t
regression_slot_stats3 | t | t | t | t
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes | mem_exceeded_count
------------------------+------------+-------------+------------+-------------+--------------------
regression_slot_stats1 | t | t | t | t | t
regression_slot_stats2 | t | t | t | t | t
regression_slot_stats3 | t | t | t | t | t
(3 rows)
RESET logical_decoding_work_mem;
@@ -53,12 +53,12 @@ SELECT pg_stat_reset_replication_slot('regression_slot_stats1');
(1 row)
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes
------------------------+------------+-------------+------------+-------------
regression_slot_stats1 | t | t | f | f
regression_slot_stats2 | t | t | t | t
regression_slot_stats3 | t | t | t | t
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes | mem_exceeded_count
------------------------+------------+-------------+------------+-------------+--------------------
regression_slot_stats1 | t | t | f | f | t
regression_slot_stats2 | t | t | t | t | t
regression_slot_stats3 | t | t | t | t | t
(3 rows)
-- reset stats for all slots
@@ -68,27 +68,27 @@ SELECT pg_stat_reset_replication_slot(NULL);
(1 row)
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes
------------------------+------------+-------------+------------+-------------
regression_slot_stats1 | t | t | f | f
regression_slot_stats2 | t | t | f | f
regression_slot_stats3 | t | t | f | f
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
slot_name | spill_txns | spill_count | total_txns | total_bytes | mem_exceeded_count
------------------------+------------+-------------+------------+-------------+--------------------
regression_slot_stats1 | t | t | f | f | t
regression_slot_stats2 | t | t | f | f | t
regression_slot_stats3 | t | t | f | f | t
(3 rows)
-- verify accessing/resetting stats for non-existent slot does something reasonable
SELECT * FROM pg_stat_get_replication_slot('do-not-exist');
slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | stats_reset
--------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+-------------
do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | mem_exceeded_count | total_txns | total_bytes | stats_reset
--------------+------------+-------------+-------------+-------------+--------------+--------------+--------------------+------------+-------------+-------------
do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
(1 row)
SELECT pg_stat_reset_replication_slot('do-not-exist');
ERROR: replication slot "do-not-exist" does not exist
SELECT * FROM pg_stat_get_replication_slot('do-not-exist');
slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | stats_reset
--------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+-------------
do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | mem_exceeded_count | total_txns | total_bytes | stats_reset
--------------+------------+-------------+-------------+-------------+--------------+--------------+--------------------+------------+-------------+-------------
do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
(1 row)
-- spilling the xact
@@ -110,12 +110,12 @@ SELECT pg_stat_force_next_flush();
(1 row)
SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
slot_name | spill_txns | spill_count
------------------------+------------+-------------
regression_slot_stats1 | t | t
regression_slot_stats2 | f | f
regression_slot_stats3 | f | f
SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, mem_exceeded_count > 0 AS mem_exceeded_count FROM pg_stat_replication_slots;
slot_name | spill_txns | spill_count | mem_exceeded_count
------------------------+------------+-------------+--------------------
regression_slot_stats1 | t | t | t
regression_slot_stats2 | f | f | f
regression_slot_stats3 | f | f | f
(3 rows)
-- Ensure stats can be repeatedly accessed using the same stats snapshot. See
@@ -159,16 +159,19 @@ SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot_stats4_twophas
(1 row)
-- Verify that the decoding doesn't spill already-aborted transaction's changes.
-- Given that there is no concurrent activities that are capturable by logical decoding,
-- mem_exceeded_count should theoretically be 1 but we check if >0 here since it's
-- more flexible for potential future changes and adequate for the testing purpose.
SELECT pg_stat_force_next_flush();
pg_stat_force_next_flush
--------------------------
(1 row)
SELECT slot_name, spill_txns, spill_count FROM pg_stat_replication_slots WHERE slot_name = 'regression_slot_stats4_twophase';
slot_name | spill_txns | spill_count
---------------------------------+------------+-------------
regression_slot_stats4_twophase | 0 | 0
SELECT slot_name, spill_txns, spill_count, mem_exceeded_count > 0 as mem_exceeded_count FROM pg_stat_replication_slots WHERE slot_name = 'regression_slot_stats4_twophase';
slot_name | spill_txns | spill_count | mem_exceeded_count
---------------------------------+------------+-------------+--------------------
regression_slot_stats4_twophase | 0 | 0 | t
(1 row)
DROP TABLE stats_test;

13
contrib/test_decoding/sql/stats.sql
View File

@@ -15,16 +15,16 @@ SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot_stats1', NULL,
SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot_stats2', NULL, NULL, 'skip-empty-xacts', '1');
SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot_stats3', NULL, NULL, 'skip-empty-xacts', '1');
SELECT pg_stat_force_next_flush();
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
RESET logical_decoding_work_mem;
-- reset stats for one slot, others should be unaffected
SELECT pg_stat_reset_replication_slot('regression_slot_stats1');
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
-- reset stats for all slots
SELECT pg_stat_reset_replication_slot(NULL);
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name;
SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes, mem_exceeded_count = 0 AS mem_exceeded_count FROM pg_stat_replication_slots ORDER BY slot_name;
-- verify accessing/resetting stats for non-existent slot does something reasonable
SELECT * FROM pg_stat_get_replication_slot('do-not-exist');
@@ -41,7 +41,7 @@ SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot_stats1', NULL
-- background transaction (say by autovacuum) happens in parallel to the main
-- transaction.
SELECT pg_stat_force_next_flush();
SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, mem_exceeded_count > 0 AS mem_exceeded_count FROM pg_stat_replication_slots;
-- Ensure stats can be repeatedly accessed using the same stats snapshot. See
-- https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i%40alap3.anarazel.de
@@ -64,8 +64,11 @@ ROLLBACK PREPARED 'test1_abort';
SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot_stats4_twophase', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
-- Verify that the decoding doesn't spill already-aborted transaction's changes.
-- Given that there is no concurrent activities that are capturable by logical decoding,
-- mem_exceeded_count should theoretically be 1 but we check if >0 here since it's
-- more flexible for potential future changes and adequate for the testing purpose.
SELECT pg_stat_force_next_flush();
SELECT slot_name, spill_txns, spill_count FROM pg_stat_replication_slots WHERE slot_name = 'regression_slot_stats4_twophase';
SELECT slot_name, spill_txns, spill_count, mem_exceeded_count > 0 as mem_exceeded_count FROM pg_stat_replication_slots WHERE slot_name = 'regression_slot_stats4_twophase';
DROP TABLE stats_test;
SELECT pg_drop_replication_slot('regression_slot_stats1'),

11
doc/src/sgml/monitoring.sgml
View File

@@ -1620,6 +1620,17 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>mem_exceeded_count</structfield><type>bigint</type>
</para>
<para>
Number of times the memory used by logical decoding has exceeded
<literal>logical_decoding_work_mem</literal>.
</para>
</entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>total_txns</structfield> <type>bigint</type>

1
src/backend/catalog/system_views.sql
View File

@@ -1063,6 +1063,7 @@ CREATE VIEW pg_stat_replication_slots AS
s.stream_txns,
s.stream_count,
s.stream_bytes,
s.mem_exceeded_count,
s.total_txns,
s.total_bytes,
s.stats_reset

8
src/backend/replication/logical/logical.c
View File

@@ -1955,10 +1955,11 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
PgStat_StatReplSlotEntry repSlotStat;
/* Nothing to do if we don't have any replication stats to be sent. */
if (rb->spillBytes <= 0 && rb->streamBytes <= 0 && rb->totalBytes <= 0)
if (rb->spillBytes <= 0 && rb->streamBytes <= 0 && rb->totalBytes <= 0 &&
rb->memExceededCount <= 0)
return;
elog(DEBUG2, "UpdateDecodingStats: updating stats %p %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64,
elog(DEBUG2, "UpdateDecodingStats: updating stats %p %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64 " %" PRId64,
rb,
rb->spillTxns,
rb->spillCount,
@@ -1966,6 +1967,7 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
rb->streamTxns,
rb->streamCount,
rb->streamBytes,
rb->memExceededCount,
rb->totalTxns,
rb->totalBytes);
@@ -1975,6 +1977,7 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
repSlotStat.stream_txns = rb->streamTxns;
repSlotStat.stream_count = rb->streamCount;
repSlotStat.stream_bytes = rb->streamBytes;
repSlotStat.mem_exceeded_count = rb->memExceededCount;
repSlotStat.total_txns = rb->totalTxns;
repSlotStat.total_bytes = rb->totalBytes;
@@ -1986,6 +1989,7 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
rb->streamTxns = 0;
rb->streamCount = 0;
rb->streamBytes = 0;
rb->memExceededCount = 0;
rb->totalTxns = 0;
rb->totalBytes = 0;
}

34
src/backend/replication/logical/reorderbuffer.c
View File

@@ -390,6 +390,7 @@ ReorderBufferAllocate(void)
buffer->streamTxns = 0;
buffer->streamCount = 0;
buffer->streamBytes = 0;
buffer->memExceededCount = 0;
buffer->totalTxns = 0;
buffer->totalBytes = 0;
@@ -3898,14 +3899,26 @@ static void
ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
{
ReorderBufferTXN *txn;
bool update_stats = true;
/*
* Bail out if debug_logical_replication_streaming is buffered and we
* haven't exceeded the memory limit.
*/
if (debug_logical_replication_streaming == DEBUG_LOGICAL_REP_STREAMING_BUFFERED &&
rb->size < logical_decoding_work_mem * (Size) 1024)
if (rb->size >= logical_decoding_work_mem * (Size) 1024)
{
/*
* Update the statistics as the memory usage has reached the limit. We
* report the statistics update later in this function since we can
* update the slot statistics altogether while streaming or
* serializing transactions in most cases.
*/
rb->memExceededCount += 1;
}
else if (debug_logical_replication_streaming == DEBUG_LOGICAL_REP_STREAMING_BUFFERED)
{
/*
* Bail out if debug_logical_replication_streaming is buffered and we
* haven't exceeded the memory limit.
*/
return;
}
/*
* If debug_logical_replication_streaming is immediate, loop until there's
@@ -3965,8 +3978,17 @@ ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
*/
Assert(txn->size == 0);
Assert(txn->nentries_mem == 0);
/*
* We've reported the memExceededCount update while streaming or
* serializing the transaction.
*/
update_stats = false;
}
if (update_stats)
UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
/* We must be under the memory limit now. */
Assert(rb->size < logical_decoding_work_mem * (Size) 1024);
}

1
src/backend/utils/activity/pgstat_replslot.c
View File

@@ -94,6 +94,7 @@ pgstat_report_replslot(ReplicationSlot *slot, const PgStat_StatReplSlotEntry *re
REPLSLOT_ACC(stream_txns);
REPLSLOT_ACC(stream_count);
REPLSLOT_ACC(stream_bytes);
REPLSLOT_ACC(mem_exceeded_count);
REPLSLOT_ACC(total_txns);
REPLSLOT_ACC(total_bytes);
#undef REPLSLOT_ACC

19
src/backend/utils/adt/pgstatfuncs.c
View File

@@ -2121,7 +2121,7 @@ pg_stat_get_archiver(PG_FUNCTION_ARGS)
Datum
pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
{
#define PG_STAT_GET_REPLICATION_SLOT_COLS 10
#define PG_STAT_GET_REPLICATION_SLOT_COLS 11
text *slotname_text = PG_GETARG_TEXT_P(0);
NameData slotname;
TupleDesc tupdesc;
@@ -2146,11 +2146,13 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 7, "stream_bytes",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 8, "total_txns",
TupleDescInitEntry(tupdesc, (AttrNumber) 8, "mem_exceeded_count",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 9, "total_bytes",
TupleDescInitEntry(tupdesc, (AttrNumber) 9, "total_txns",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 10, "stats_reset",
TupleDescInitEntry(tupdesc, (AttrNumber) 10, "total_bytes",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 11, "stats_reset",
TIMESTAMPTZOID, -1, 0);
BlessTupleDesc(tupdesc);
@@ -2173,13 +2175,14 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
values[4] = Int64GetDatum(slotent->stream_txns);
values[5] = Int64GetDatum(slotent->stream_count);
values[6] = Int64GetDatum(slotent->stream_bytes);
values[7] = Int64GetDatum(slotent->total_txns);
values[8] = Int64GetDatum(slotent->total_bytes);
values[7] = Int64GetDatum(slotent->mem_exceeded_count);
values[8] = Int64GetDatum(slotent->total_txns);
values[9] = Int64GetDatum(slotent->total_bytes);
if (slotent->stat_reset_timestamp == 0)
nulls[9] = true;
nulls[10] = true;
else
values[9] = TimestampTzGetDatum(slotent->stat_reset_timestamp);
values[10] = TimestampTzGetDatum(slotent->stat_reset_timestamp);
/* Returns the record as Datum */
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));

2
src/include/catalog/catversion.h
View File

@@ -57,6 +57,6 @@
*/
/* yyyymmddN */
#define CATALOG_VERSION_NO 202510082
#define CATALOG_VERSION_NO 202510083
#endif

6
src/include/catalog/pg_proc.dat
View File

@@ -5691,9 +5691,9 @@
{ oid => '6169', descr => 'statistics: information about replication slot',
proname => 'pg_stat_get_replication_slot', provolatile => 's',
proparallel => 'r', prorettype => 'record', proargtypes => 'text',
proallargtypes => '{text,text,int8,int8,int8,int8,int8,int8,int8,int8,timestamptz}',
proargmodes => '{i,o,o,o,o,o,o,o,o,o,o}',
proargnames => '{slot_name,slot_name,spill_txns,spill_count,spill_bytes,stream_txns,stream_count,stream_bytes,total_txns,total_bytes,stats_reset}',
proallargtypes => '{text,text,int8,int8,int8,int8,int8,int8,int8,int8,int8,timestamptz}',
proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o}',
proargnames => '{slot_name,slot_name,spill_txns,spill_count,spill_bytes,stream_txns,stream_count,stream_bytes,mem_exceeded_count,total_txns,total_bytes,stats_reset}',
prosrc => 'pg_stat_get_replication_slot' },
{ oid => '6230', descr => 'statistics: check if a stats object exists',

1
src/include/pgstat.h
View File

@@ -395,6 +395,7 @@ typedef struct PgStat_StatReplSlotEntry
PgStat_Counter stream_txns;
PgStat_Counter stream_count;
PgStat_Counter stream_bytes;
PgStat_Counter mem_exceeded_count;
PgStat_Counter total_txns;
PgStat_Counter total_bytes;
TimestampTz stat_reset_timestamp;

3
src/include/replication/reorderbuffer.h
View File

@@ -690,6 +690,9 @@ struct ReorderBuffer
int64 streamCount; /* streaming invocation counter */
int64 streamBytes; /* amount of data decoded */
/* Number of times the logical_decoding_work_mem limit has been reached */
int64 memExceededCount;
/*
* Statistics about all the transactions sent to the decoding output
* plugin

3
src/test/regress/expected/rules.out
View File

@@ -2140,11 +2140,12 @@ pg_stat_replication_slots| SELECT s.slot_name,
s.stream_txns,
s.stream_count,
s.stream_bytes,
s.mem_exceeded_count,
s.total_txns,
s.total_bytes,
s.stats_reset
FROM pg_replication_slots r,
LATERAL pg_stat_get_replication_slot((r.slot_name)::text) s(slot_name, spill_txns, spill_count, spill_bytes, stream_txns, stream_count, stream_bytes, total_txns, total_bytes, stats_reset)
LATERAL pg_stat_get_replication_slot((r.slot_name)::text) s(slot_name, spill_txns, spill_count, spill_bytes, stream_txns, stream_count, stream_bytes, mem_exceeded_count, total_txns, total_bytes, stats_reset)
WHERE (r.datoid IS NOT NULL);
pg_stat_slru| SELECT name,
blks_zeroed,