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272248a0c1
Previously, we relied on HEAP2_NEW_CID records and XACT_INVALIDATION records to know if the transaction has modified the catalog, and that information is not serialized to snapshot. Therefore, after the restart, if the logical decoding decodes only the commit record of the transaction that has actually modified a catalog, we will miss adding its XID to the snapshot. Thus, we will end up looking at catalogs with the wrong snapshot. To fix this problem, this changes the snapshot builder so that it remembers the last-running-xacts list of the decoded RUNNING_XACTS record after restoring the previously serialized snapshot. Then, we mark the transaction as containing catalog changes if it's in the list of initial running transactions and its commit record has XACT_XINFO_HAS_INVALS. To avoid ABI breakage, we store the array of the initial running transactions in the static variables InitialRunningXacts and NInitialRunningXacts, instead of storing those in SnapBuild or ReorderBuffer. This approach has a false positive; we could end up adding the transaction that didn't change catalog to the snapshot since we cannot distinguish whether the transaction has catalog changes only by checking the COMMIT record. It doesn't have the information on which (sub) transaction has catalog changes, and XACT_XINFO_HAS_INVALS doesn't necessarily indicate that the transaction has catalog change. But that won't be a problem since we use snapshot built during decoding only to read system catalogs. On the master branch, we took a more future-proof approach by writing catalog modifying transactions to the serialized snapshot which avoids the above false positive. But we cannot backpatch it because of a change in the SnapBuild. Reported-by: Mike Oh Author: Masahiko Sawada Reviewed-by: Amit Kapila, Shi yu, Takamichi Osumi, Kyotaro Horiguchi, Bertrand Drouvot, Ahsan Hadi Backpatch-through: 10 Discussion: https://postgr.es/m/81D0D8B0-E7C4-4999-B616-1E5004DBDCD2%40amazon.com
45 lines
1.6 KiB
Plaintext
45 lines
1.6 KiB
Plaintext
Parsed test spec with 2 sessions
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starting permutation: s0_init s0_begin s0_savepoint s0_truncate s1_checkpoint s1_get_changes s0_commit s0_begin s0_insert s1_checkpoint s1_get_changes s0_commit s1_get_changes
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step s0_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
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?column?
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--------
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init
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(1 row)
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step s0_begin: BEGIN;
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step s0_savepoint: SAVEPOINT sp1;
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step s0_truncate: TRUNCATE tbl1;
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step s1_checkpoint: CHECKPOINT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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----
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(0 rows)
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step s0_commit: COMMIT;
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step s0_begin: BEGIN;
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step s0_insert: INSERT INTO tbl1 VALUES (1);
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step s1_checkpoint: CHECKPOINT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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---------------------------------------
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BEGIN
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table public.tbl1: TRUNCATE: (no-flags)
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COMMIT
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(3 rows)
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step s0_commit: COMMIT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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-------------------------------------------------------------
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BEGIN
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table public.tbl1: INSERT: val1[integer]:1 val2[integer]:null
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COMMIT
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(3 rows)
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?column?
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--------
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stop
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(1 row)
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