Horton

Re: Postgres, fsync, and OSs (specifically linux)

Craig Ringer <craig@2ndquadrant.com>

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From: Craig Ringer <craig@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Simon Riggs <simon@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2018-04-30T05:03:24Z
Lists: pgsql-hackers 
Hrm, something else that just came up. On 9.6+ we use sync_file_range.
It's surely going to eat errors:

        rc = sync_file_range(fd, offset, nbytes,
                             SYNC_FILE_RANGE_WRITE);

        /* don't error out, this is just a performance optimization */
        if (rc != 0)
        {
            ereport(WARNING,
                    (errcode_for_file_access(),
                     errmsg("could not flush dirty data: %m")));
        }

so that has to panic too.

I'm very suspicious about the safety of the msync() path too.

I'll post an update to my PANIC-everywhere patch that add these cases.

Commits

  1. PANIC on fsync() failure.

  2. Fix and improve pg_atomic_flag fallback implementation.