On Sat, Mar 21, 2015 at 8:54 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:

> Stephen Frost <sfr...@snowman.net> writes:
> > At the moment, one could look at our default postgresql.conf and the
> > "turns forced synchronization on or off" and think it's something akin
> > or somehow related to synchronous_commit (which is completely different,
> > but the options are right next to each other..).
>
> > How about a big warning around fsync and make it more indepenent from
> > the options around it?
>
> Yeah, the main SGML docs are reasonably clear about the risks of fsync,
> but postgresql.conf doesn't give you any hint that it's dangerous.  Now
> I'm not entirely sure that people who frob postgresql.conf without having
> read the docs can be saved from themselves, but we could do something
> like this:
>
>  # - Settings -
>
>  #wal_level = minimal                   # minimal, archive, hot_standby,
> or logical
>                                         # (change requires restart)
>  #fsync = on                            # turns forced synchronization on
> or off
> +                                       # (fsync=off is dangerous, read the
> +                                       # (manual before using it)
>  #synchronous_commit = on               # synchronization level;
>                                         # off, local, remote_write, or on
>  #wal_sync_method = fsync               # the default is the first option
>                                         # supported by the operating
> system:
>
> Also, I think the short description "turns forced synchronization on or
> off" could stand improvement; it really conveys zero information.  Maybe
> something like "force data to disk when committing"?
>
> Also, whatever we do here should be reflected into the description strings
> in guc.c.
>

"​enables or disables data durability ​promise of ACID." ?

David J.

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