Re: High context switches occurring

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(at)2ndquadrant(dot)com]
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

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