Re: Turning off HOT/Cleanup sometimes

On 4/22/15 11:37 AM, Jim Nasby wrote:
> On 4/21/15 4:07 PM, Peter Eisentraut wrote:
>> On 4/21/15 4:45 PM, Jim Nasby wrote:
>> 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.
> 
> My thought was that the foreground queries would send page IDs to the
> bgworker via a shmq. If the queries have to do much waiting at all on IO
> then I'd expect the bgworker to be able to keep pace with a bunch of
> them since it's just grabbing buffers that are already in the pool (and
> only those in the pool; it wouldn't make sense for it to pull it back
> from the kernel, let alone disk).
> 
> We'd need to code this so that if a queue fills up the query doesn't
> block; we just skip that opportunity to prune. I think that'd be fine.

I think a "to-clean-up map" would work better.  But basically we need a
way to remember where to clean up later if we're not going to do it in
the foreground.