Re: autovacuum truncate exclusive lock round two

On Wed, Dec 5, 2012 at 10:16 PM, Jan Wieck <JanWieck@yahoo.com> wrote:
> On 12/5/2012 2:00 PM, Robert Haas wrote:
>>
>> Many it'd be sensible to relate the retry time to the time spend
>> vacuuming the table.  Say, if the amount of time spent retrying
>> exceeds 10% of the time spend vacuuming the table, with a minimum of
>> 1s and a maximum of 1min, give up.  That way, big tables will get a
>> little more leeway than small tables, which is probably appropriate.
>
> That sort of "dynamic" approach would indeed be interesting. But I fear that
> it is going to be complex at best. The amount of time spent in scanning
> heavily depends on the visibility map. The initial vacuum scan of a table
> can take hours or more, but it does update the visibility map even if the
> vacuum itself is aborted later. The next vacuum may scan that table in
> almost no time at all, because it skips all blocks that are marked "all
> visible".

Well, if that's true, then there's little reason to worry about giving
up quickly, because the next autovacuum a minute later won't consume
many resources.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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