On Tue, Feb 28, 2012 at 1:15 AM, Ants Aasma <ants.aa...@eesti.ee> wrote: > My hypothesis for the TPS regression is that it is due to write combining. > When the workload is mainly bound by I/O, every little bit that can be saved > helps the bottomline. Larger scalefactors don't get the benefit because > there is less write combining going on overall.
This is an interesting hypothesis which I think we can test. I'm thinking of writing a quick patch (just for testing, not for commit) to set a new buffer flag BM_BGWRITER_CLEANED to every buffer the background writer cleans. Then we can keep a count of how often such buffers are dirtied before they're evicted, vs. how often they're evicted before they're dirtied. If any significant percentage of them are redirtied before they're evicted, that would confirm this hypothesis. At any rate I think the numbers would be interesting to see. -- 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