From 8175a7d11f70589f6b44e28a8dd804f7542d0bbf Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Mon, 7 Oct 2024 14:53:18 +0530 Subject: [PATCH] Fix fetching default toast value during decoding of in-progress transactions. During logical decoding of in-progress transactions, we perform the toast table scan while fetching the default toast value for an attribute. We forgot to initialize the flag during this scan to indicate that the system table scan is in progress. We need this flag to ensure that during logical decoding we never directly access the tableam or heap APIs because we check for concurrent aborts only in systable_* APIs. Reported-by: Alexander Lakhin Author: Takeshi Ideriha, Hou Zhijie Reviewed-by: Amit Kapila, Hou Zhijie Backpatch-through: 14 Discussion: https://postgr.es/m/18641-6687273b7f15269d@postgresql.org --- contrib/test_decoding/expected/stream.out | 20 ++++++++++++++++++++ contrib/test_decoding/sql/stream.sql | 18 ++++++++++++++++++ src/backend/access/index/genam.c | 16 ++++++++++++++++ 3 files changed, 54 insertions(+) diff --git a/contrib/test_decoding/expected/stream.out b/contrib/test_decoding/expected/stream.out index 0f21dcb8e0..2e319a8941 100644 --- a/contrib/test_decoding/expected/stream.out +++ b/contrib/test_decoding/expected/stream.out @@ -106,6 +106,26 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'incl committing streamed transaction (17 rows) +-- Test that accessing a TOAST table in streaming mode is allowed. +-- Create a table with a column that uses a TOASTed default value. +-- (temporarily hide query, to avoid the long CREATE TABLE stmt) +\set ECHO none +BEGIN; +INSERT INTO test_tab SELECT repeat('a', 6000) || g.i FROM generate_series(1, 350) g(i); +-- Force WAL flush, so that the above changes will be streamed. +SELECT 'force flush' FROM pg_switch_wal(); + ?column? +------------- + force flush +(1 row) + +SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1'); + count +------- + 315 +(1 row) + +COMMIT; DROP TABLE stream_test; SELECT pg_drop_replication_slot('regression_slot'); pg_drop_replication_slot diff --git a/contrib/test_decoding/sql/stream.sql b/contrib/test_decoding/sql/stream.sql index 4feec62972..9502a6d87c 100644 --- a/contrib/test_decoding/sql/stream.sql +++ b/contrib/test_decoding/sql/stream.sql @@ -44,5 +44,23 @@ toasted-123456789012345678901234567890123456789012345678901234567890123456789012 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1'); +-- Test that accessing a TOAST table in streaming mode is allowed. + +-- Create a table with a column that uses a TOASTed default value. +-- (temporarily hide query, to avoid the long CREATE TABLE stmt) +\set ECHO none +SELECT 'CREATE TABLE test_tab (a text DEFAULT ''' || string_agg('toast value', '') || ''');' FROM generate_series(1, 4000) +\gexec +\set ECHO all + +BEGIN; +INSERT INTO test_tab SELECT repeat('a', 6000) || g.i FROM generate_series(1, 350) g(i); + +-- Force WAL flush, so that the above changes will be streamed. +SELECT 'force flush' FROM pg_switch_wal(); + +SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1'); +COMMIT; + DROP TABLE stream_test; SELECT pg_drop_replication_slot('regression_slot'); diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c index ede9660c9e..76d3edd470 100644 --- a/src/backend/access/index/genam.c +++ b/src/backend/access/index/genam.c @@ -703,6 +703,14 @@ systable_beginscan_ordered(Relation heapRelation, index_rescan(sysscan->iscan, key, nkeys, NULL, 0); sysscan->scan = NULL; + /* + * If CheckXidAlive is set then set a flag to indicate that system table + * scan is in-progress. See detailed comments in xact.c where these + * variables are declared. + */ + if (TransactionIdIsValid(CheckXidAlive)) + bsysscan = true; + return sysscan; } @@ -747,6 +755,14 @@ systable_endscan_ordered(SysScanDesc sysscan) index_endscan(sysscan->iscan); if (sysscan->snapshot) UnregisterSnapshot(sysscan->snapshot); + + /* + * Reset the bsysscan flag at the end of the systable scan. See detailed + * comments in xact.c where these variables are declared. + */ + if (TransactionIdIsValid(CheckXidAlive)) + bsysscan = false; + pfree(sysscan); }