On Thu, Aug 25, 2016 at 7:45 PM, Robert Haas <robertmh...@gmail.com> wrote:
> On Thu, Aug 25, 2016 at 1:43 PM, Josh Berkus <j...@agliodbs.com> wrote: > > On 08/25/2016 01:12 PM, Robert Haas wrote: > >>> I agree that #4 is best. I'm not sure it's worth the cost. I'm not > worried > >>> > at all about the risk of master/slave sync thing, per previous > statement. > >>> > But if it does have performance implications, per Andres suggestion, > then > >>> > making it configurable at initdb time probably comes with a cost > that's not > >>> > worth paying. > >> At this point it's hard to judge, because we don't have any idea what > >> the cost might be. I guess if we want to pursue this approach, > >> somebody will have to code it up and benchmark it. But what I'm > >> inclined to do for starters is put together a patch to go from 16MB -> > >> 64MB. Committing that early this cycle will give us time to > >> reconsider if that turns out to be painful for reasons we haven't > >> thought of yet. And give tool authors time to make adjustments, if > >> any are needed. > > > > The one thing I'd be worried about with the increase in size is folks > > using PostgreSQL for very small databases. If your database is only > > 30MB or so in size, the increase in size of the WAL will be pretty > > significant (+144MB for the base 3 WAL segments). I'm not sure this is > > a real problem which users will notice (in today's scales, 144MB ain't > > much), but if it turns out to be, it would be nice to have a way to > > switch it back *just for them* without recompiling. > > I think you may be forgetting that "the base 3 WAL segments" is no > longer the default configuration. checkpoint_segments=3 is history; > we now have max_wal_size=1GB, which is a maximum of 64 WAL segments, > not 3. > > And obviously that'd be 16 files if we increase the wal segment size. So the actual maximum size doesn't change, except you can currently set max_wal_size to something lower than 64Mb. If we change, the minimum value would become 64Mb, I assume. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/
