On Thu, Dec 30, 2010 at 06:15:34PM -0600, Jim Nasby wrote: > On Dec 28, 2010, at 7:59 AM, Nicolas Haller wrote: > > I use a new box with 4GB RAM as a pgsql server. In pgsql, you can > > set the effective_cache_size to indicate the memory available to cache > > disk I/O. > > As "recommended", my box use 1300MB to shared buffers (IPC shared memory) > > and 2700 Mo to disk cache.
> That's probably not a great mix unless your workload is very > read-heavy. Writes will push data through shared buffers back into the > OS, which will also try to cache it, so you'll end up with > double-buffering. Interresting. My DB is not heavily loaded yet so I don't see any problem at this time. I just follow recommendations. I thought Postgresql write and sync disk after writing WAL or doing a checkpoint. > > If I look memory usage in top, it say: > > Mem: 1154M Active, 1911M Inact, 601M Wired, 112M Cache, 417M Buf, 148M Free > The Cache reported by top in FreeBSD isn't filesystem cache; it's a > cache for some internal stuff. Buf are filesystem buffers, but they're > not the only mechanism for the OS to cache data. Most data is actually > cached via active and inactive pages. Ok, so when Postgresql doing a query for a second time for (very simple) example, FreeBSD can retrieve data from inactive mem too? Someone knows if there is a page which explains FreeBSD mechanisms about memory and fs cache management? I think I must read something on it :-) Thanks, -- Nicolas Haller _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "[email protected]"
