From: | Mark Mielke <mark(at)mark(dot)mielke(dot)cc> |
---|---|
To: | Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc> |
Cc: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Pavan Deolasee <pavan(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: HOT patch, missing things |
Date: | 2007-08-07 19:43:55 |
Message-ID: | 46B8CB7B.7090105@mark.mielke.cc |
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Lists: | pgsql-hackers |
Stefan Kaltenbrunner wrote:
> Heikki Linnakangas wrote:
>
>> 2. Pointer swinging. At the moment, after a row is HOT updated, the only
>> way to get rid of the redirecting line pointer is to run VACUUM FULL or
>> CLUSTER (or delete or cold update the row and vacuum). If we want to
>> implement pointer swinging before release, we have to get started now.
>> If we're happy to release without it and address the issue in later
>> releases if it seems important, we need to make a conscious decision on
>> that, now. I personally think we can release without it.
>>
> hmm - I don't really understand most of the stuff behind HOT but does
> this mean that VACUUM FULL (or CLUSTER) is becoming a recommended or
> even required routine maintenance task for people using HOT ?
>
No more than before. See the comment "or delete or cold update the row
and vacuum". The row couldn't be cleared by vacuum before unless
delete/update. Based on the above, it appears that every time an HOT
update occurs, 4 to 8 bytes might get wasted in the page. Eventually
this fills the page and a regular cold update is required and it is cleared.
Cheers,
mark
--
Mark Mielke <mark(at)mielke(dot)cc>
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