Re: Seq scans status update

CK Tan wrote:
> If it is convenient for you, could you run my patch against the same
> hardware and data to get some numbers on select for comparison? Although
> we don't address updates, copy, or inserts, we are definitely getting
> at least 20% improvement in scans here without poisoning the bufpool for
> large tables.

Sure, here you are:

copy-cktan-big | 00:10:08.843126
copy-cktan-big | 00:10:17.767606
copy-cktan-big | 00:09:37.797059
copy_nowal-cktan-big | 00:05:12.305025
copy_nowal-cktan-big | 00:05:10.518417
copy_nowal-cktan-big | 00:05:03.472939
select-cktan-big | 00:03:27.655982
select-cktan-big | 00:01:55.496408
select-cktan-big | 00:01:31.693856
select-cktan-big | 00:01:12.705268
select-cktan-big | 00:01:12.478247
select-cktan-big | 00:01:10.866484
vacuum_clean-cktan-big | 00:03:05.340875
vacuum_clean-cktan-big | 00:01:12.428317
vacuum_clean-cktan-big | 00:01:13.179957
vacuum_clean-cktan-big | 00:01:10.438888
vacuum_hintbits-cktan-big | 00:03:58.78208
vacuum_hintbits-cktan-big | 00:04:02.515778
vacuum_hintbits-cktan-big | 00:04:19.083402
vacuum_hintbits-cktan-big | 00:04:11.170831
copy-cktan-med | 00:02:19.413484
copy-cktan-med | 00:02:22.270497
copy-cktan-med | 00:02:22.297946
copy_nowal-cktan-med | 00:01:31.192601
copy_nowal-cktan-med | 00:01:17.736356
copy_nowal-cktan-med | 00:01:32.272778
select-cktan-med | 00:00:03.774974
select-cktan-med | 00:00:01.279276
select-cktan-med | 00:00:01.297703
select-cktan-med | 00:00:01.304129
select-cktan-med | 00:00:01.297048
select-cktan-med | 00:00:01.306073
vacuum_clean-cktan-med | 00:00:01.820733
vacuum_clean-cktan-med | 00:00:01.755684
vacuum_clean-cktan-med | 00:00:01.755659
vacuum_clean-cktan-med | 00:00:01.750972
vacuum_hintbits-cktan-med | 00:00:01.58744
vacuum_hintbits-cktan-med | 00:00:06.216038
vacuum_hintbits-cktan-med | 00:00:02.201789
vacuum_hintbits-cktan-med | 00:00:36.494427

Select performance looks the same as with Simon's/my patch.

That 20% gain must be hardware-dependent. My interpretation is that the
CPU savings from more efficient cache usage only matters when the I/O
bandwidth is high enough that CPU becomes the bottleneck.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com