Prevent unintended dropping of active replication origins. Commit 5b148706c5 exposed 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 commit 5b148706c5, 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 <[email protected]> Author: Hayato Kuroda <[email protected]> Reviewed-by: Shveta Malik <[email protected]> Reviewed-by: Amit Kapila <[email protected]> Discussion: https://postgr.es/m/ty4pr01mb169077ee72abe9e55baf162d494...@ty4pr01mb16907.jpnprd01.prod.outlook.com Discussion: https://postgr.es/m/CAMPB6wfe4zLjJL8jiZV5kjjpwBM2=rtrme0ucl7ra4l8mtv...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/e385a4e2fd8ead796014a82dd6165f6027255b46 Modified Files -------------- .../expected/parallel_session_origin.out | 46 +++++++- .../specs/parallel_session_origin.spec | 6 +- src/backend/replication/logical/origin.c | 120 +++++++++++++++------ 3 files changed, 137 insertions(+), 35 deletions(-)
