Re: slow bitmap heap scans on pg 9.2 - Mailing list pgsql-performance

From Steve Singer
Subject Re: slow bitmap heap scans on pg 9.2
Date
Msg-id 5165FBA1.90704@ca.afilias.info
Whole thread Raw
In response to Re: slow bitmap heap scans on pg 9.2  (Jeff Janes <jeff.janes@gmail.com>)
Responses Re: slow bitmap heap scans on pg 9.2
List pgsql-performance
On 13-04-10 02:06 PM, Jeff Janes wrote:
> On Wed, Apr 10, 2013 at 6:49 AM, Steve Singer <ssinger@ca.afilias.info
> <mailto:ssinger@ca.afilias.info>> wrote:
>

> I think the index recheck means your bitmap is overflowing (i.e. needing
> more space than work_mem) and so keeping only the pages which have at
> least one match, which means all rows in those pages need to be
> rechecked.  How many rows does the table have?  You might be essentially
> doing a seq scan, but with the additional overhead of the bitmap
> machinery.  Could you do "explain (analyze,buffers)", preferably with
> track_io_timing set to on?
>

table_b has 1,530,710,469 rows

Attached is the output with track_io_timings and buffers.





>   Cheers,
>
> Jeff


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