basebackup: do not verify checksums on pages from before enabling Enabling data checksums in a running cluster changes the state to "on" before the checkpoint which flushes the pages the worker rewrote. A base backup which started before that transition absorbs the barrier mid-run and starts verifying pages whose on-disk copies legitimately lack checksums, and whose LSNs predate the backup start, so the LSN check does not skip them either. The backup fails with bogus corruption warnings. The same applies to checksums being disabled and re-enabled while the backup runs: hint bits set while checksums were off reach disk without a checksum update and without moving the page LSN, tripping verification once the re-enabling completes.
To fix, verify checksums only while they have been continuously enabled since the checkpoint the backup started from: track the location of the last XLOG2_CHECKSUMS record inserted or replayed, and verify only when the state is "on" and the last change predates the backup start. The starting checkpoint then guarantees that every page flushed before it has a checksum written, and any later change disables verification for the rest of the backup. A standby loses the tracked location when restarting, while pg_control already carries the new state, so it could reach consistency below the record and serve base backups with the location unknown. To prevent this, replaying XLOG2_CHECKSUMS advances minRecoveryPoint to the record, like XLOG_PARAMETER_CHANGE does. The tests hold the enabling between the state change and its final checkpoint with injection points, straddling it with backups on the primary and across a standby crash-restart. Author: Zsolt Parragi <[email protected]> Reviewed-by: Bertrand Drouvot <[email protected]> Reviewed-by: Daniel Gustafsson <[email protected]> Discussion: https://postgr.es/m/CAN4CZFP=-cVVVPue+e8qqPtDfuLuQn=zb4mw_c9-ncru2wq...@mail.gmail.com Backpatch-through: 19 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/55edc7907b87db6c0b3257b4d7083c2b9fcbfd69 Modified Files -------------- doc/src/sgml/ref/pg_basebackup.sgml | 6 + src/backend/access/transam/xlog.c | 58 +++++ src/backend/backup/basebackup.c | 73 +++++- src/include/access/xlog.h | 1 + src/test/modules/test_checksums/meson.build | 2 + .../test_checksums/t/010_backup_straddle.pl | 260 +++++++++++++++++++++ .../test_checksums/t/011_standby_straddle.pl | 249 ++++++++++++++++++++ 7 files changed, 640 insertions(+), 9 deletions(-)
