Re: Some thoughts about i/o priorities and throttling vacuum

Rod Taylor wrote:

> On Fri, 2003-10-17 at 10:22, Tom Lane wrote:
> 
>>Shridhar Daithankar <shridhar_daithankar@persistent.co.in> writes:
>>
>>>What part of plain vacuum takes disk bandwidth?
>>
>>Reading (and possibly rewriting) all the pages.
> 
> 
> Would it be possible for the backend to keep a list of the first N (N
> being a large number but not significant in memory usage) pages it has
> deleted tuples out of and a second list of N pages it has inserted
> tuples into.

That is RSM, reclaimable space map. It is on TODO.

> After the transaction has completed and there is an idle period (say 1/4
> second between transaction) it can pass the insert information on a
> rollback and delete information on a commit to a separate backend.
> 
> This 'vacuum' backend could then prioritize garbage collection for the
> pages it knows have been changed performing a single page vacuum when a
> specific page has seen a high level of reported activity.
> 
> If this daemon could also get a hold of information about idleness of IO
> in general the decision about what to vacuum and when may be better
> (heavily hit pages during peak periods, all reports pages on medium
> load). When completely idle, run through the entire system to get back
> as much as possible.

I agree. This seems to be the best way of dealing with things. Of course, 
probably there are details we are missing here, but in general its good.
 Shridhar