Re: WIP: Avoid creation of the free space map for small tables

Thanks,

On Sun, Dec 30, 2018 at 3:49 AM John Naylor <jcnaylor@gmail.com> wrote:
> On 12/29/18, Mithun Cy <mithun.cy@enterprisedb.com> wrote:
> > Results are execution time(unit ms) taken by copy statement when number of
> > records  equal to exact number which fit HEAP_FSM_CREATION_THRESHOLD = 4
> > pages. For fill factor 20 it is till tid (3, 43) and for scale factor 70
> > till tid (3, 157). Result is taken as a median of 10 runs.
>
> > So 2-3% consistent regression, And on every run I can see for patch v11
> > execution time is slightly more than base.
>
> Thanks for testing!
>
> > I also tried to insert more
> > records till 8 pages and same regression is observed! So I guess even
> > HEAP_FSM_CREATION_THRESHOLD = 4 is not perfect!
>
> That's curious, because once the table exceeds the threshold, it would
> be allowed to update the FSM, and in the process write 3 pages that it
> didn't have to in the 4 page test. The master branch has the FSM
> already, so I would expect the 8 page case to regress more.

I tested with configuration HEAP_FSM_CREATION_THRESHOLD = 4 and just
tried to insert till 8 blocks to see if regression is carried on with
further inserts.

> What I can do later is provide a supplementary patch to go on top of
> mine that only checks the last block. If that improves performance,
> I'll alter my patch to only check every other page.

Running callgrind for same test shows below stats
Before patch
==========
Number of calls                function_name
2000                                 heap_multi_insert
2000                                 RelationGetBufferForTuple
3500                                 ReadBufferBI

After Patch
=========
Number of calls                function_name
2000                                 heap_multi_insert
2000                                 RelationGetBufferForTuple
5000                                 ReadBufferBI

I guess Increase in ReadBufferBI() calls might be the reason which is
causing regression. Sorry I have not investigated it. I will check
same with your next patch!

-- 
Thanks and Regards
Mithun Chicklore Yogendra
EnterpriseDB: http://www.enterprisedb.com