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

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