Re: Turning off HOT/Cleanup sometimes

On Tue, Apr 21, 2015 at 05:07:52PM -0400, Peter Eisentraut wrote:
> On 4/21/15 4:45 PM, Jim Nasby wrote:
> > This comment made me wonder... has anyone considered handing the pruning
> > work off to a bgworker, at least for SELECTs? That means the selects
> > themselves wouldn't be burdened by the actual prune work, only in
> > notifying the bgworker. While that's not going to be free, presumably
> > it's a lot cheaper...
> 
> The nice thing about having foreground queries to the light cleanup is
> that they can work in parallel and naturally hit the interesting parts
> of the table first.
> 
> In order for a background worker to keep up with some of the workloads
> that have been presented as counterexamples, you'd need multiple
> background workers operating in parallel and preferring to work on
> certain parts of a table.  That would require a lot more sophisticated
> job management than we currently have for, say, autovacuum.

Well, the visibility map tells us where _not_ to clean up, so using
another map to tell use _where_ to cleanup might make sense.  However,
the density of the map might be low enough that a list makes more sense,
as you suggested.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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