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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'),