Re: Remove fsync ON/OFF as a visible option?

Stephen Frost <sfrost(at)snowman(dot)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.

regards, tom lane