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Fix on-demand SLRU download on standby starting at WAL segment boundary (#8031)

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If a standby is started right after switching to a new WAL segment, the
request in the SLRU download request would point to the beginning of the
segment (e.g. 0/5000000), while the not-modified-since LSN would point
to just after the page header (e.g. 0/5000028). It's effectively the
same position, as there cannot be any WAL records in between, but the
pageserver rightly errors out on any request where the request LSN <
not-modified since LSN.

To fix, round down the not-modified since LSN to the beginning of the
page like the request LSN.

Fixes issue #8030
This commit is contained in:
Heikki Linnakangas
2024-06-13 00:31:31 +03:00
committed by GitHub
parent ad0ab3b81b
commit dc2ab4407f
2 changed files with 32 additions and 2 deletions
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4
pgxn/neon/pagestore_smgr.c
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@@ -3112,12 +3112,12 @@ neon_read_slru_segment(SMgrRelation reln, const char* path, int segno, void* buf
request_lsn = UINT64_MAX;
/*
* GetRedoStartLsn() returns LSN of basebackup. We know that the SLRU
* GetRedoStartLsn() returns LSN of the basebackup. We know that the SLRU
* segment has not changed since the basebackup, because in order to
* modify it, we would have had to download it already. And once
* downloaded, we never evict SLRU segments from local disk.
*/
not_modified_since = GetRedoStartLsn();
not_modified_since = nm_adjust_lsn(GetRedoStartLsn());
SlruKind kind;