| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Anthony Iliopoulos <ailiop(at)altatus(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Geoff Winkless <pgsqladmin(at)geoff(dot)dj>, Craig Ringer <craig(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Catalin Iacob <iacobcatalin(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: PostgreSQL's handling of fsync() errors is unsafe and risks data loss at least on XFS |
| Date: | 2018-04-09 20:04:20 |
| Message-ID: | 20180409200420.2shb4xygozkl3zr2@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2018-04-09 21:54:05 +0200, Tomas Vondra wrote:
> Isn't the expectation that when a fsync call fails, the next one will
> retry writing the pages in the hope that it succeeds?
Some people expect that, I personally don't think it's a useful
expectation.
We should just deal with this by crash-recovery. The big problem I see
is that you always need to keep an file descriptor open for pretty much
any file written to inside and outside of postgres, to be guaranteed to
see errors. And that'd solve that. Even if retrying would work, I'd
advocate for that (I've done so in the past, and I've written code in pg
that panics on fsync failure...).
What we'd need to do however is to clear that bit during crash
recovery... Which is interesting from a policy perspective. Could be
that other apps wouldn't want that.
I also wonder if we couldn't just somewhere read each relevant mounted
filesystem's errseq value. Whenever checkpointer notices before
finishing a checkpoint that it has changed, do a crash restart.
Greetings,
Andres Freund
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