Re: Database performs massive reads when I'm doing writes.

On Thu, Jun 6, 2013 at 9:53 AM, Ray Cote
<rgacote(at)appropriatesolutions(dot)com>wrote:

> Starting a few days ago we started to see a strange behavior where writing
> to the database causes massive read operations.
> For example, I have a table that needs to be updated every night (about
> 20,000 rows).
> Using Django ORM, we update them one item at a time.
> Usually the overall process takes a few minutes; it is now taking hours
> (like over 15 hours).
>
> Running atop, we're seeing Read Disk values in the range of 147.2M/10s and
> Write Disk values in the range of 16K/10s.
> Together, the Disk throughput is in the high 90% and frequently hits 100%.
>
> When I'm not writing to the database, it becomes quiet without any disk
> activity.
>
> This is a 256 MByte system and atop shows we're not swapping
>

Is autovacuum set to 'on'?
Possibly there is bloat in your table and indexes; what happens to the
system after you issue a manual "VACUUM ANALYZE VERBOSE"? If that helps,
you might need to make your autovacuum settings more aggressive.