On Tuesday, December 22, 2020 6:25 PM, Amit Kapila wrote:
> Attached, please find the updated patch with the following modifications, (a)
> updated comments at various places especially to tell why this is a safe
> optimization, (b) merged the patch for extending the smgrnblocks and
> vacuum optimization patch, (c) made minor cosmetic changes and ran
> pgindent, and (d) updated commit message. BTW, this optimization will help
> not only vacuum but also truncate when it is done in the same transaction in
> which the relation is created. I would like to see certain tests to ensure that
> the value we choose for BUF_DROP_FULL_SCAN_THRESHOLD is correct. I
> see that some testing has been done earlier [1] for this threshold but I am not
> still able to conclude. The criteria to find the right threshold should be what is
> the maximum size of relation to be truncated above which we don't get
> benefit with this optimization.
>
> One idea could be to remove "nBlocksToInvalidate <
> BUF_DROP_FULL_SCAN_THRESHOLD" part of check "if (cached &&
> nBlocksToInvalidate < BUF_DROP_FULL_SCAN_THRESHOLD)" so that it
> always use optimized path for the tests. Then use the relation size as
> NBuffers/128, NBuffers/256, NBuffers/512 for different values of shared
> buffers as 128MB, 1GB, 20GB, 100GB.
Alright. I will also repeat the tests with the different threshold settings,
and thank you for the tip.
> Apart from tests, do let me know if you are happy with the changes in the
> patch? Next, I'll look into DropRelFileNodesAllBuffers() optimization patch.
Thank you, Amit.
That looks more neat, combining the previous patches 0002-0003, so I am +1
with the changes because of the clearer explanations for the threshold and
optimization path in DropRelFileNodeBuffers. Thanks for cleaning my patch sets.
Hope we don't forget the 0001 patch's assertion in smgrextend() to ensure that we
do it safely too and that we are not InRecovery.
> [1] -
> https://www.postgresql.org/message-id/OSBPR01MB234176B1829AECFE9
> FDDFCC2EFE90%40OSBPR01MB2341.jpnprd01.prod.outlook.com
Regards,
Kirk Jamison