Simon, I tested it by running two of those simultaneous queries (the 'unoptimized' one), and it doesn't make any difference whether vm.max-readahead is 256 or 2048...the modified query runs in a snap. Thanks, Anjan -----Original Message----- From: Anjan Dave Sent: Wednesday, November 23, 2005 1:33 PM To: Simon Riggs Cc: Scott Marlowe; Tom Lane; Vivek Khera; Postgresql Performance Subject: Re: [PERFORM] High context switches occurring The offending SELECT query that invoked the CS storm was optimized by folks here last night, so it's hard to say if the VM setting made a difference. I'll give it a try anyway. Thanks, Anjan -----Original Message----- From: Simon Riggs [mailto:simon@xxxxxxxxxxxxxxx] Sent: Wednesday, November 23, 2005 1:14 PM To: Anjan Dave Cc: Scott Marlowe; Tom Lane; Vivek Khera; Postgresql Performance Subject: Re: [PERFORM] High context switches occurring On Tue, 2005-11-22 at 18:17 -0500, Anjan Dave wrote: > It's mostly a 'read' application, I increased the vm.max-readahead to > 2048 from the default 256, after which I've not seen the CS storm, > though it could be incidental. Can you verify this, please? Turn it back down again, try the test, then reset and try the test. If that is a repeatable way of recreating one manifestation of the problem then we will be further ahead than we are now. Thanks, Best Regards, Simon Riggs ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
