Re: sequential scan result order vs performance

From: Andres Freund <andres(at)anarazel(dot)de>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: sequential scan result order vs performance
Date: 2016-10-30 07:43:12
Views: Raw Message | Whole Thread | Download mbox | Resend email
Lists: pgsql-hackers


On 2016-10-30 00:36:55 -0700, Andres Freund wrote:
> It's quite easy to change iteration so we start with the latest item,
> and iterate till the first, rather than the other way round. In
> benchmarks with somewhat wide columns and aggregation, this yields
> speedups of over 30%, before hitting other bottlenecks.

One more point: Over IM Robert commented that it's not guaranteed that
itemid order correlates precisely with reverse "tuple data" order. After
PageRepairFragmentation() that'll not be the case anymore. That's true,
but I suspect in many cases with larger analytics queries the
correlation will still be significant, and we also could make it
guaranteed with the price of making PageRepairFragmentation() a bit more


Andres Freund

In response to

Browse pgsql-hackers by date

  From Date Subject
Next Message Andres Freund 2016-10-30 07:52:34 Re: JIT compiler for expressions
Previous Message Greg Stark 2016-10-30 07:40:56 Re: JIT compiler for expressions