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Commit5b148706c5exposed functionality that allows multiple processes to use the same replication origin, enabling non-builtin logical replication solutions to implement parallel apply for large transactions. With this functionality, if two backends acquire the same replication origin and one of them resets it first, the acquired_by flag is cleared without acknowledging that another backend is still actively using the origin. This can lead to the origin being unintentionally dropped. If the shared memory for that dropped origin is later reused for a newly created origin, the remaining backend that still holds a pointer to the old memory may inadvertently advance the LSN of a completely different origin, causing unpredictable behavior. Although the underlying issue predates commit5b148706c5, it did not surface earlier because the internal parallel apply worker mechanism correctly coordinated origin resets and drops. This commit resolves the problem by introducing a reference counter for replication origins. The reference count increases when a backend sets the origin and decreases when it resets it. Additionally, the backend that first acquires the origin will not release it until all other backends using the origin have released it as well. The patch also prevents dropping a replication origin when acquired_by is zero but the reference counter is nonzero, covering the scenario where the first session exits without properly releasing the origin. Author: Hou Zhijie <houzj.fnst@fujitsu.com> Author: Hayato Kuroda <kuroda.hayato@fujitsu.com> Reviewed-by: Shveta Malik <shveta.malik@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Discussion: https://postgr.es/m/TY4PR01MB169077EE72ABE9E55BAF162D494B5A@TY4PR01MB16907.jpnprd01.prod.outlook.com Discussion: https://postgr.es/m/CAMPB6wfe4zLjJL8jiZV5kjjpwBM2=rTRme0UCL7Ra4L8MTVdOg@mail.gmail.com
61 lines
2.1 KiB
Python
61 lines
2.1 KiB
Python
# Test parallel replication origin manipulations; ensure local_lsn can be
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# updated by all attached sessions.
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setup
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{
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SELECT pg_replication_origin_create('origin');
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CREATE UNLOGGED TABLE local_lsn_store (session int, lsn pg_lsn);
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}
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teardown
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{
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SELECT pg_replication_origin_drop('origin');
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DROP TABLE local_lsn_store;
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}
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session "s0"
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setup { SET synchronous_commit = on; }
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step "s0_setup" { SELECT pg_replication_origin_session_setup('origin'); }
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step "s0_is_setup" { SELECT pg_replication_origin_session_is_setup(); }
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step "s0_add_message" {
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SELECT 1
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FROM pg_logical_emit_message(true, 'prefix', 'message on s0');
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}
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step "s0_store_lsn" {
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INSERT INTO local_lsn_store
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SELECT 0, local_lsn FROM pg_replication_origin_status;
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}
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step "s0_compare" {
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SELECT s0.lsn < s1.lsn
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FROM local_lsn_store as s0, local_lsn_store as s1
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WHERE s0.session = 0 AND s1.session = 1;
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}
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step "s0_reset" { SELECT pg_replication_origin_session_reset(); }
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session "s1"
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setup { SET synchronous_commit = on; }
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step "s1_setup" {
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SELECT pg_replication_origin_session_setup('origin', pid)
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FROM pg_stat_activity
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WHERE application_name = 'isolation/parallel_session_origin/s0';
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}
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step "s1_is_setup" { SELECT pg_replication_origin_session_is_setup(); }
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step "s1_add_message" {
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SELECT 1
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FROM pg_logical_emit_message(true, 'prefix', 'message on s1');
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}
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step "s1_store_lsn" {
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INSERT INTO local_lsn_store
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SELECT 1, local_lsn FROM pg_replication_origin_status;
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}
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step "s1_reset" { SELECT pg_replication_origin_session_reset(); }
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# Firstly s0 attaches to a origin and s1 attaches to the same. Both sessions
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# commits a transaction and store the local_lsn of the replication origin.
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# Compare LSNs and expect latter transaction (done by s1) has larger local_lsn.
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permutation "s0_setup" "s0_is_setup" "s1_setup" "s1_is_setup" "s0_add_message" "s0_store_lsn" "s1_add_message" "s1_store_lsn" "s0_compare" "s1_reset" "s0_reset"
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# Test that the origin cannot be released if another session is actively using
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# it.
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permutation "s0_setup" "s0_is_setup" "s1_setup" "s1_is_setup" "s0_reset" "s1_reset" "s0_reset"
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