Ensure that a standby is able to follow a primary on a newer timeline

Enterprise / PostgreSQL - Fujii Masao [postgresql.org] - 14 January 2021 03:27 UTC

Commit 709d003fbd refactored WAL-reading code, but accidentally caused WalSndSegmentOpen() to fail to follow a timeline switch while reading from a historic timeline. This issue caused a standby to fail to follow a primary on a newer timeline when WAL archiving is enabled.

If there is a timeline switch within the segment, WalSndSegmentOpen() should read from the WAL segment belonging to the new timeline. But previously since it failed to follow a timeline switch, it tried to read the WAL segment with old timeline. When WAL archiving is enabled, that WAL segment with old timeline doesn't exist because it's renamed to .partial. This leads a primary to have tried to read non-existent WAL segment, and which caused replication to faill with the error "ERROR: requested WAL segment ... has already been removed".

This commit fixes WalSndSegmentOpen() so that it's able to follow a timeline switch, to ensure that a standby is able to follow a primary on a newer timeline even when WAL archiving is enabled.

This commit also adds the regression test to check whether a standby is able to follow a primary on a newer timeline when WAL archiving is enabled.

Back-patch to v13 where the bug was introduced.

fef5b47f6b Ensure that a standby is able to follow a primary on a newer timeline.
src/backend/replication/walsender.c | 2 +-
src/test/recovery/t/004_timeline_switch.pl | 42 +++++++++++++++++++++++++++---
2 files changed, 40 insertions(+), 4 deletions(-)

Upstream: git.postgresql.org


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