Fix VM clear WAL logging by registering VM blocks Heap WAL records that clear bits on the visibility map (like inserts and deletes) did not register the visibility map blocks they modified. Because the WAL summarizer only records registered blocks, an incremental backup taken over such operations would omit the changed VM pages. On restore, the VM would retain stale all-visible/all-frozen bits, which can cause wrong results from index-only scans and incorrect relfrozenxid advancement due to vacuum page skipping.
Not registering the VM buffer also meant we never emitted FPIs of VM pages when clearing bits. A torn VM page won't raise an error because the VM is read with ZERO_ON_ERROR; with checksums on, it would be detected and zeroed, but with checksums off, it is accepted as-is and can lead to data corruption. Fix this by registering the VM buffer in the WAL record when clearing VM bits. The VM buffer must now be locked throughout the critical section that modifies the VM and heap pages and emits the WAL record. This can slow down operations that clear the VM, since the VM lock is held longer and VM FPIs may be emitted, but it is required for correctness. Note that this fix does not repair existing incremental backups. Author: Melanie Plageman <[email protected]> Author: Andres Freund <[email protected]> Reviewed-by: Robert Haas <[email protected]> Reviewed-by: Andrey Borodin <[email protected]> Discussion: https://postgr.es/m/flat/CAAKRu_bn%2Be7F4yPFBgFbnP%2BsyJRKyNK092bjD2LKvZW7O4Svag> Backpatch-through: 17 Branch ------ REL_17_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/c0d9864f5ce47902dd258bb61dd89ada6d020b55 Modified Files -------------- contrib/pg_surgery/heap_surgery.c | 40 +- src/backend/access/heap/heapam.c | 650 +++++++++++++++++++++++++------- src/backend/access/heap/visibilitymap.c | 34 +- src/bin/pg_walsummary/t/002_blocks.pl | 7 +- src/include/access/heapam_xlog.h | 18 +- src/include/access/visibilitymap.h | 2 + 6 files changed, 596 insertions(+), 155 deletions(-)
