On 2018/05/23 10:36, Bruce Momjian wrote:
> On Wed, May 23, 2018 at 10:28:41AM +0900, Amit Langote wrote:
>>> Uh, we already have this in the release notes:
>>>
>>> Allow faster partition elimination during query processing (Amit
>>> Langote, David Rowley, Dilip Kumar)
>>>
>>> This speeds access to partitioned tables with many partitions.
>>>
>>> Do you want me to add the git commit hash to this release note entry?
>>
>> I suppose you meant the above as an entry for performance improvement of
>> partition "pruning". The commit I quoted is concerned with making "tuple
>> routing" a bit faster, but as David said that's not making it as fast as
>> it could really be. So, we should hold off from touting it as an
>> improvement at this point and I have to agree. Sorry for the noise.
>
> OK, no problem. So _finding_ the rows is faster, but adding rows to
> partitioned tables with many partitions is still slow, got it.
Yeah.
To be honest, even _finding_ is not yet performing the best it could be,
which I guess David would chime in to say. We know what needs to be fixed
to get the close-to-ideal performance there, but didn't have time to do it
for PG 11. To clarify, what changed is that we replaced constraint
exclusion, which has to consider the partition constraint of *all*
partitions individually, as an algorithm for partition pruning by a faster
alternative that only looks at the parent table's partition descriptor.
That gives a good boost but that's not the end of it. Moreover, addition
of this new pruning algorithm enabled the development of execution time
pruning which is a completely new feature.
Thanks,
Amit