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Re: Idea how to get rid of Bitmap Heap Scan

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: "Michael N(dot) Mikhulya" <m(dot)mikhulya(at)gmail(dot)com>, Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Idea how to get rid of Bitmap Heap Scan
Date: 2009-12-20 11:37:45
Message-ID: 407d949e0912200337u7c027709mce4cc135bc64279d@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Sun, Dec 20, 2009 at 2:11 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Dec 18, 2009 at 12:29 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
>> A word of warning, in my experience the hardest part for changes like
>> this isn't the executor changes (which in this case wouldn't be far
>> from easy) but the planner changes to detect when this new plan would
>> be better.
>
> There's also the problem of making the visibility map crash-safe.  I
> think I heard you might have some ideas on that one - has it been
> discussed on -hackers?

Not sure what ideas you mean.

In the original poster's plan that isn't an issue. We could scan the
index, perform the joins and restriction clauses, and only check the
visibility on the resulting tuples which slip through them all. That
would be possible even without crash-safe visibility bits.

-- 
greg

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Subject: Re: Idea how to get rid of Bitmap Heap Scan
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