Re: Relation extension scalability

On Thu, Mar 31, 2016 at 4:28 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Thu, Mar 31, 2016 at 12:59 AM, Dilip Kumar <dilipbalaut(at)gmail(dot)com>
> wrote:
> > On Tue, Mar 29, 2016 at 10:08 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > wrote:
> >> Yes, that makes sense. One more point is that if the reason for v13
> >> giving better performance is extra blocks (which we believe in certain
> cases
> >> can leak till the time Vacuum updates the FSM tree), do you think it
> makes
> >> sense to once test by increasing lockWaiters * 20 limit to may be
> >> lockWaiters * 25 or lockWaiters * 30.
> >
> >
> > I tested COPY 10000 record, by increasing the number of blocks just to
> find
> > out why we are not as good as V13
> > with extraBlocks = Min( lockWaiters * 40, 2048) and got below results..
> >
> > COPY 10000
> > --------------------
> > Client Patch(extraBlocks = Min( lockWaiters * 40, 2048))
> > -------- ---------
> > 16 752
> > 32 708
> >
> > This proves that main reason of v13 being better is its adding extra
> blocks
> > without control.
> > though v13 is better than these results, I think we can get that also by
> > changing multiplier and max limit .
> >
> > But I think we are ok with the max size as 4MB (512 blocks) right?
>
> Yeah, kind of. But obviously if we could make the limit smaller
> without hurting performance, that would be better.
>
> Per my note yesterday about performance degradation with parallel
> COPY, I wasn't able to demonstrate that this patch gives a consistent
> performance benefit on hydra - the best result I got was speeding up a
> 9.5 minute load to 8 minutes where linear scalability would have been
> 2 minutes.

Is this test for unlogged tables? As far as I understand this patch will
show benefit if Data and WAL are on separate disks or if you test them with
unlogged tables, otherwise the WAL contention supersedes the benefit of
this patch.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com