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Re: half the query time in an unnecessary(?) sort?

From: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: half the query time in an unnecessary(?) sort?
Date: 2005-04-26 05:45:57
Message-ID: 426DD595.1040608@cheapcomplexdevices.com (view raw or flat)
Thread:
Lists: pgsql-performance
Josh Berkus wrote: [quoted out of order]
>Ron,
> 
> Looking at your analyze, though, I think it's not the sort that's taking the 
> time as it is that the full sorted entity_id column won't fit in work_mem.  
> Try increasing it?

Yup, that indeed fixed this particular query since neither table was
particularly large.


> It still has to sort because the clustering isn't guarenteed to be 100%.   

I guess I was contemplating whether or not there are some conditions
where it could be 100% (perhaps combined with Hannu's read only
table speculation).

> However, such sorts should be very quick as they have little work to do.

True, so long as the table can fit in work-mem.   For much larger tables
IMHO it'd be nice to be able to simply do a seq-scan on them if there were
some way of knowing that they were sorted.


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