| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | HECTOR INGERTO <hector_25e(at)hotmail(dot)com> |
| Cc: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Magnus Hagander <magnus(at)hagander(dot)net>, "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: | 2023-01-17 21:38:43 |
| Message-ID: | Y8cVY4Fn8yOZTgjN@momjian.us |
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| Lists: | pgsql-general |
On Tue, Jan 17, 2023 at 03:22:02PM +0000, HECTOR INGERTO wrote:
> > Another case: a transaction COMMITs, and a slightly later transaction reads
> the data
> > and sets a hint bit. If the snapshot of the file system with the data
> directory in it
> > is slightly later than the snapshot of the file system with "pg_wal", the
> COMMIT might
> > not be part of the snapshot, but the hint bit could be.
> >
> > Then these uncommitted data could be visible if you recover from the
> snapshot.
> >
> > Yours,
> > Laurenz Albe
>
>
>
> Thank you all. I have it clearer now.
>
>
>
> As a last point. Making the snapshot to the WAL dataset first or last would
> make any difference?
How would you know which WAL snapshot to use, and if there is any
missing data between them?
I have often wondered if we could document rules where multiple
asychronous snapshots would be safe but have never gotten very far.
--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com
Embrace your flaws. They make you human, rather than perfect,
which you will never be.
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