Hello again. So sorry for resurrecting such an old thread but the problem still persists - I've just had very little to report on, until now... > > That latter test - won't that pretty much just read from the page > cache? > > 'sync' may well have forced dirty pages to disk but does it actually > > evict them to? > > Basically, the cache is avoided because of the size of the file. > 6000000 blocks at 8k exceeds the size of RAM in the machine, so it > *should* miss the cache and hit the disk directly. :) OK, I did this during the problematic time and write speeds (sustained) are in the order of 250MB/s :) It took just 3m21s to write all ~50GB. We get read speeds of a wonderfully massive ~530MB/s - the whole file read in just 1m30s. All metrics gathered with iostat -p <devices> -m 1. Now, what I have noticed is this; we run two databases on this one machine. One (DB) is completely operable in a normal way during the slow period and the other is not. This (unresponsive) database has just two client processes connected - one is writing, the other is (meant to be) reading. Neither registers in pg_locks - one does not block the other at the DB level. However the write process (INSERTs) is writing between 5 and 10 MB/s. The read process (a SELECT or EXPLAIN) just spins the CPU at 100% and register 0.0 MB/s - yet it should be reading *a lot* of data. So does PostgreSQL somehow (or have I misconfigured it to) always prioritise writes over reads? I'm still at a loss! Any further pointers would be appreciated. Jim PS. This is with the deadline scheduler and with each block device set with --setra 8192. > > Anyway, that is off topic... perhaps ;) > > > > Thanks again, > > > > Jim > > > > Cheers > > Martin ============================================= Romax Technology > Limited Rutherford House Nottingham Science & Technology Park > Nottingham, NG7 2PZ England Telephone numbers: +44 (0)115 951 88 00 > (main) For other office locations see: > http://www.romaxtech.com/Contact ================================= > =============== E-mail: info@xxxxxxxxxxxxx Website: www.romaxtech.com > ================================= ================ Confidentiality > Statement This transmission is for the addressee only and contains > information that is confidential and privileged. Unless you are the > named addressee, or authorised to receive it on behalf of the > addressee you may not copy or use it, or disclose it to anyone else. > If you have received this transmission in error please delete from > your system and contact the sender. Thank you for your cooperation. > ================================================= > -- Jim Vanns Systems Programmer Framestore -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
