On 2013-06-03 16:41:32 -0700, Peter Geoghegan wrote: > On Mon, Jun 3, 2013 at 3:16 PM, Kevin Grittner <kgri...@ymail.com> wrote: > >> But it seems like the kernel is disposed to cache large amounts > >> of dirty data for an unbounded period of time even if the I/O > >> system is completely idle, > > > > It's not unbounded time. Last I heard, the default was 30 seconds. > > I'm pretty sure it is unbounded. The VM documentation is a bit vague > on what dirty_expire_centisecs actually means, which is I presume > where this number comes from. It says: > > "This tunable is used to define when dirty data is old enough to be eligible > for writeout by the pdflush daemons. It is expressed in 100'ths of a second. > Data which has been dirty in-memory for longer than this interval will be > written out next time a pdflush daemon wakes up." > > So I think the a pdflush daemon won't necessarily wake up until > dirty_background_bytes or dirty_background_ratio have been exceeded, > regardless of this threshold. Am I mistaken?
Without having it checked again, afair it should wakeup every dirty_writeback_centisecs which is something like 5seconds. All that has pretty significantly changed - and imo improved! - in the last year or so of kernel development. Unfortunately it will take a while till we commonly see those kernels being used :( Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
