On Mon, Jan 31, 2011 at 11:51 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Mon, Jan 31, 2011 at 11:29 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> That sounds like you have an entirely wrong mental model of where the >>> cost comes from. Those times are not independent. > >> Yeah, Greg Smith made the same point a week or three ago. But it >> seems to me that there is potential value in overlaying the write and >> sync phases to some degree. For example, if the write phase is spread >> over 15 minutes and you have 30 files, then by, say, minute 7, it's a >> probably OK to flush the file you wrote first. > > Yeah, probably, but we can't do anything as stupid as file-by-file.
Eh? > I wonder whether it'd be useful to keep track of the total amount of > data written-and-not-yet-synced, and to issue fsyncs often enough to > keep that below some parameter; the idea being that the parameter would > limit how much dirty kernel disk cache there is. Of course, ideally the > kernel would have a similar tunable and this would be a waste of effort > on our part... It's not clear to me how you'd maintain that information without it turning into a contention bottleneck. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
