Re: Why do we let autovacuum give up? - Mailing list pgsql-hackers

From Andres Freund
Subject Re: Why do we let autovacuum give up?
Date
Msg-id 20140123235521.GM7182@awork2.anarazel.de
Whole thread Raw
In response to Re: Why do we let autovacuum give up?  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Why do we let autovacuum give up?  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On 2014-01-23 16:15:50 -0500, Tom Lane wrote:
> [ thinks... ]  It's possible that what you saw is not the
> kick-out-autovacuum-entirely behavior, but the behavior added in commit
> bbb6e559c, whereby vacuum (auto or regular) will skip over pages that it
> can't immediately get an exclusive buffer lock on.  On a heavily used
> table, we might skip the same page repeatedly, so that dead tuples don't
> get cleaned for a long time.

I don't think it's too likely as an explanation here. Such workloads are
likely to fill a page with only dead tuples, right? Once all tuples are
safely dead they will be killed from the btree which should cause the
page not to be visited anymore and thus safely vacuumable.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services



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