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"? > I agree the current description is lacking, but that proposed wording would be a better description of synchronous_commit. It is checkpointing and flush-WAL-before-data where fsync=off does its damage. "Force data to disk when needed for integrity"? Or just don't describe what it is at all, and refer to the documentation only. Cheers, Jeff
