Re: fsync-pgdata-on-recovery tries to write to more files than previously

On 05/26/2015 11:58 AM, Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> OK, I'm late to the party. But why exactly are we syncing absolutely
>> everything? That seems over-broad.
> If we try to be selective, we risk errors of omission, which no one would
> ever notice until someone's data got eaten in a low-probability crash
> scenario. It seems more robust (at least to me) to fsync everything we
> can find. That does require more thought about error cases than went
> into the original patch ... but I think that we need more thought about
> error cases even if we do try to be selective.
>
> One thing perhaps we *should* be selective about, though, is which
> symlinks we try to follow. I think that a good case could be made
> for ignoring symlinks everywhere except in the pg_tablespace directory.
> If we did, that would all by itself take care of the Debian scenario,
> if I understand that case correctly.

People have symlinked the xlog directory. I've done it myself in the
past. A better rule might be to ignore symlinks unless either they are
in pg_tblspc or they are in the data directory and their name starts
with "pg_".

cheers

andrew