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? https://www.kernel.org/doc/Documentation/sysctl/vm.txt -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
