Re: possible bug in 8.4 - Mailing list pgsql-hackers

From Grzegorz Jaskiewicz
Subject Re: possible bug in 8.4
Date
Msg-id 77D255AA-8E66-4D2E-AEDF-664FC36F7FC6@pointblue.com.pl
Whole thread Raw
In response to Re: possible bug in 8.4  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On 2008-12-19, at 13:07, Tom Lane wrote:

> Grzegorz Jaskiewicz <gj@pointblue.com.pl> writes:
>> Filter: (NOT (hashed subplan))
>           ^^^^^^^^^^^^^^
>
> If 8.3 does that, and 8.4 doesn't, it's most likely because you are
> using different work_mem settings.

you're right, as always :)

My point is, why is planner choosing plan on 8.4 that's obviously more  
expensive ? even without sort_mem (work_mem) set to higher value ?
Obviously the plan is quite expensive, so probably sorting it on disc  
- would be still cheaper.
The example is quite unrealistic, but I am trying different simple  
things to test planner differences between these two versions, and see  
if there's any improvement/regression.
This time I will set both work_mem to same value :)





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