Re: speedup tidbitmap patch: cache page

From: Teodor Sigaev <teodor(at)sigaev(dot)ru>
To: David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: speedup tidbitmap patch: cache page
Date: 2014-12-23 11:24:43
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> Oh, that makes sense. Though I wonder if you need to clear the caches at all
> when calling tbm_lossify(). Surely it never becomes un-lossified and plus, at
> least for lossy_page it would never be set to the current page anyway, it's
> either going to be set to InvalidBlockNumber, or some other previous page that
agree, fixed

> was lossy. I also can't quite see the need to set page to NULL. Surely doing
> this would just mean we'd have to lookup the page again once tbm_lossify() is
> called if the next loop happened to be the same page? I think this would only be
> needed if the hash lookup was going to return a new instance of the page after
> we've lossified it, which from what I can tell won't happen.

Page could become an invalid pointer, because during tbm_mark_page_lossy()
called from tbm_lossify() it could be freed.

> I've also attached some benchmark results using your original table from
> up-thread. It seems that the caching if the page was seen as lossy is not much
> of a help in this test case. Did you find another one where you saw some better
> gains?

All what I found is about 0.5%... v3 contains your comments but it doesn't use
lossy_page cache.
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru

Attachment Content-Type Size
tbm_cachepage-2.3.patch.gz application/x-gzip 892 bytes
tbm_cachepage-3.patch.gz application/x-gzip 751 bytes

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