| From: | HECTOR INGERTO <hector_25e(at)hotmail(dot)com> |
|---|---|
| To: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Magnus Hagander <magnus(at)hagander(dot)net> |
| Cc: | "pgsql-general(at)postgresql(dot)org <pgsql-general(at)postgresql(dot)org>" <pgsql-general(at)postgresql(dot)org> |
| Subject: | RE: Are ZFS snapshots unsafe when PGSQL is spreading through multiple zpools? |
| Date: | 2023-01-16 14:37:23 |
| Message-ID: | GV1P189MB2036AFE96E22BF5830C1E22CF5C19@GV1P189MB2036.EURP189.PROD.OUTLOOK.COM |
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| Lists: | pgsql-general |
> The database relies on the data being consistent when it performs crash recovery.
> Imagine that a checkpoint is running while you take your snapshot. The checkpoint
> syncs a data file with a new row to disk. Then it writes a WAL record and updates
> the control file. Now imagine that the table with the new row is on a different
> file system, and your snapshot captures the WAL and the control file, but not
> the new row (it was still sitting in the kernel page cache when the snapshot was taken).
> You end up with a lost row.
>
> That is only one scenario. Many other ways of corruption can happen.
Can we say then that the risk comes only from the possibility of a checkpoint running inside the time gap between the non-simultaneous snapshots?
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