Re: Autovacuum Improvements

You're saying that the dirtyness of a table is proportional to when you
plan on vacuuming it next.  I don't see that connection at all.  The
only correlation I might see is if it happens to be 5:59 AM when your DB
decides your table is dirty, and your maintenance window closes at 6:00
AM.  Then you have to program the maintenance window to gracefully
unplug the vacuum.

Currently, autovacuum runs every minute and checks to see if any tables
meet the requirements for vacuuming.  Are the requirements the amount of
time a vacuum would take, or the raw number of dirty tuples?  One might
be a function of the other, for sure, but exactly what does the
autovacuumer use to decide when to clean?

--
Brandon Aiken
CS/IT Systems Engineer
-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org] On Behalf Of Matthew
O'Connor
Sent: Tuesday, December 19, 2006 5:37 PM
To: Glen Parker
Cc: Postgres general mailing list
Subject: Re: [GENERAL] Autovacuum Improvements

Glen Parker wrote:
> Erik Jones wrote:
>> Matthew O'Connor wrote:
>>> Glen Parker wrote:
>>>> If it isn't there somewhere already, I would ask to add:
>>>>  Expose a very easy way to discover autovacuum's opinion about a
>>>> particular table, for example "table_needs_vacuum(oid)", ignoring
>>>> any time constraints that may be in place.
>>>
>>> This might be a nice feature however in the presence of the much
>>> talked about but not yet developed maintenance window concept, I'm
>>> not sure how  this should work.  That is, during business hours the
>>> table doesn't need vacuuming, but it will when the evening
>>> maintenance window opens up.
>  >
>> Well, what he's saying is, "Not taking into account any
>> time/maintenance windows, does this table need vacuuming?"
>
> Correct.  IOW, "does it need it?", not "would you actually do it at
this
> time?"...

I understand that, but it's a subjective question.  The only question
autovacuum answers is "Am I going to vacuum this table now?", so in the
current setup you probably could create a function that answers your
question, I was just pointing out in the future when maintenance windows

  get implemented that this question becomes less clear.

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