On 2018-01-10 00:25:08 +0100, Andreas Joseph Krogh wrote: > På tirsdag 09. januar 2018 kl. 23:42:45, skrev Rob Sargent < > robjsargent@xxxxxxxxx <mailto:robjsargent@xxxxxxxxx>>: > > > On 01/09/2018 03:30 PM, Andreas Joseph Krogh wrote: > På tirsdag 09. januar 2018 kl. 23:06:06, skrev Andres Freund < > andres@xxxxxxxxxxx <mailto:andres@xxxxxxxxxxx>>: > Hi, > > On 2018-01-09 21:47:17 +0100, Andreas Joseph Krogh wrote: > > Does PG use HW-accellerated crc if CPU supports it[1]? > > Yes we do, for WAL checksums. The page checksums are a different > algorithm though, one which has the advantage of being SIMD compatible. > > The checksum computations have some impact, but if there's bigger impact > it's much more likely to be related to the fact that some hint bit > writes to a page now needs to be WAL logged. > > But SIMD-instructions are also HW-accellerated by modern CPUs IIUC? Sure. Still measurable, but even if weren't, it's irrelevant given my primary point: > The checksum computations have some impact, but if there's bigger impact > it's much more likely to be related to the fact that some hint bit > writes to a page now needs to be WAL logged. which isn't mitigated by SIMD / hardware CRC / whatnot. Greetings, Andres Freund
