From: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
---|---|
To: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Set visibility map bit after HOT prune |
Date: | 2012-12-15 12:42:13 |
Message-ID: | CABOikdN3_FFb4qbaSrNhn-SCV2kNS63aGVimRbUzvS9YUFVHNQ@mail.gmail.com |
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We discussed this idea in the past [1] and Robert recently again
mentioned this in another thread [2]. Please see a rebased/revised
patch attached with the mail. This is mostly similar to what I's
submitted in [1] except some additions to also compute visibility
cut-off XID. I also removed a warning that I'd added to the previous
patch to report the case when the page's all-visible bit is already
set, but our HOT prune scan finds it otherwise. This is not to hide
the warning the earlier reviewer had reported, but I think its not
required because we do those consistency checks at other places
anyways.
I've run several rounds of pgbench (-s 10 -c 10 -T 300) and did not
find any issues. I don't see noticeable performance again/drop. But
again pgbench may not be the most suitable test benchmark to test
this. I think we will see positive differences in vacuum scans and
also queries that are benefited from index-only scans. An early
setting of the visibility map bit can help those two scenarios.
Thanks,
Pavan
1. http://archives.postgresql.org/pgsql-hackers/2010-02/msg02344.php
2. http://archives.postgresql.org/message-id/CA+TgmoZHWN1+N_CGD3hx=DJPHkd69c8x2r2EiQ5=c8yxNrc8wA@mail.gmail.com
--
Pavan Deolasee
http://www.linkedin.com/in/pavandeolasee
Attachment | Content-Type | Size |
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hot-prune-set-all-visible-v2.patch | application/octet-stream | 7.4 KB |
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