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Commit5f79580

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Fix memory lifetime issues of replication slot stats.
When accessing replication slot stats, introduced in9868167,pgstat_read_statsfiles() reads the data into newly allocatedmemory. Unfortunately the current memory context at that point is thecallers, leading to leaks and use-after-free dangers.The fix is trivial, explicitly use pgStatLocalContext. There's somepotential for further improvements, but that's outside of the scope ofthis bugfix.No backpatch necessary, feature is only in HEAD.Author: Andres Freund <andres@anarazel.de>Discussion:https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i@alap3.anarazel.de
1 parent7094564 commit5f79580

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3 files changed

+28
-1
lines changed

3 files changed

+28
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lines changed

‎contrib/test_decoding/expected/stats.out

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@@ -101,6 +101,22 @@ SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count F
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regression_slot | t | t
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(1 row)
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-- Ensure stats can be repeatedly accessed using the same stats snapshot. See
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-- https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i%40alap3.anarazel.de
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BEGIN;
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SELECT slot_name FROM pg_stat_replication_slots;
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slot_name
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-----------------
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regression_slot
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(1 row)
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SELECT slot_name FROM pg_stat_replication_slots;
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slot_name
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-----------------
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regression_slot
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(1 row)
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COMMIT;
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DROP FUNCTION wait_for_decode_stats(bool);
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DROP TABLE stats_test;
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SELECT pg_drop_replication_slot('regression_slot');

‎contrib/test_decoding/sql/stats.sql

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@@ -59,6 +59,13 @@ SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL,
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SELECT wait_for_decode_stats(false);
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SELECT slot_name, spill_txns>0AS spill_txns, spill_count>0AS spill_countFROM pg_stat_replication_slots;
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-- Ensure stats can be repeatedly accessed using the same stats snapshot. See
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-- https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i%40alap3.anarazel.de
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BEGIN;
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SELECT slot_nameFROM pg_stat_replication_slots;
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SELECT slot_nameFROM pg_stat_replication_slots;
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COMMIT;
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DROPFUNCTION wait_for_decode_stats(bool);
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DROPTABLE stats_test;
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SELECT pg_drop_replication_slot('regression_slot');

‎src/backend/postmaster/pgstat.c

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Original file line numberDiff line numberDiff line change
@@ -5568,7 +5568,9 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
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HASH_ELEM |HASH_BLOBS |HASH_CONTEXT);
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/* Allocate the space for replication slot statistics */
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replSlotStats=palloc0(max_replication_slots*sizeof(PgStat_ReplSlotStats));
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replSlotStats=MemoryContextAllocZero(pgStatLocalContext,
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max_replication_slots
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*sizeof(PgStat_ReplSlotStats));
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nReplSlotStats=0;
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/*
@@ -6323,6 +6325,8 @@ pgstat_clear_snapshot(void)
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pgStatDBHash=NULL;
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localBackendStatusTable=NULL;
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localNumBackends=0;
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replSlotStats=NULL;
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nReplSlotStats=0;
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}
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