Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

On Thu, Mar 23, 2017 at 12:19 AM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
>
> Ok, no problem. I did some tests on AWS i2.xlarge instance (4 vCPU, 30GB
> RAM, attached SSD) and results are shown below. But I think it is important
> to get independent validation from your side too, just to ensure I am not
> making any mistake in measurement. I've attached naively put together
> scripts which I used to run the benchmark. If you find them useful, please
> adjust the paths and run on your machine.
>
> I reverted back to UNLOGGED table because with WAL the results looked very
> weird (as posted earlier) even when I was taking a CHECKPOINT before each
> set and had set max_wal_size and checkpoint_timeout high enough to avoid any
> checkpoint during the run. Anyways, that's a matter of separate
> investigation and not related to this patch.
>
> I did two kinds of tests.
> a) update last column of the index
> b) update second column of the index
>
> v19 does considerably better than even master for the last column update
> case and pretty much inline for the second column update test. The reason is
> very clear because v19 determines early in the cycle that the buffer is
> already full and there is very little chance of doing a HOT update on the
> page. In that case, it does not check any columns for modification.
>

That sounds like you are dodging the actual problem.  I mean you can
put that same PageIsFull() check in master code as well and then you
will most probably again see the same regression.  Also, I think if we
test at fillfactor 80 or 75 (which is not unrealistic considering an
update-intensive workload), then we might again see regression.

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