Re: Automatic free space map filling

On Fri, 2006-04-28 at 15:58 -0400, Bruce Momjian wrote:
> Tom Lane wrote:
> > Alvaro Herrera <alvherre@commandprompt.com> writes:
> > > So for you it would certainly help a lot to be able to vacuum the first
> > > X pages of the big table, stop, release locks, create new transaction,
> > > continue with the next X pages, lather, rinse, repeat.
> > 
> > > This is perfectly doable, it only needs enough motivation from a
> > > knowledgeable person.
> > 
> > Bruce and I were discussing this the other day; it'd be pretty easy to
> > make plain VACUUM start a fresh transaction immediately after it
> > finishes a scan heap/clean indexes/clean heap cycle.  The infrastructure
> > for this (in particular, session-level locks that won't be lost by
> > closing the xact) is all there.  You'd have to figure out how often to
> > start a new xact ... every cycle is probably too often, at least for
> > smaller maintenance_work_mem settings ... but it'd not be hard or
> > involve any strange changes in system semantics.
> 
> Should this be a TODO?  One item of discussion was taht people should
> just increase their workmem so the job can be done faster in larger
> batches.

Yes, I think it should be a todo item.

Csaba's point was that it was the duration a VACUUM transaction was held
open that caused problems. Increasing maintenance_work_mem won't help
with that problem.

This would then allow a VACUUM to progress with a high vacuum_cost_delay
without any ill effects elsewhere in the system.

--  Simon Riggs              EnterpriseDB   http://www.enterprisedb.com