Re: [HACKERS] Checksums by default?

On Fri, Feb 24, 2017 at 10:09:50PM +0200, Ants Aasma wrote:
> On Fri, Feb 24, 2017 at 9:37 PM, Bruce Momjian <bruce@momjian.us> wrote:
> > Oh, that's why we will hopefully eventually change the page checksum
> > algorithm to use the special CRC32 instruction, and set a new checksum
> > version --- got it.  I assume there is currently no compile-time way to
> > do this.
> 
> Using CRC32 as implemented now for the WAL would be significantly
> slower than what we have now due to instruction latency. Even the best
> theoretical implementation using the CRC32 instruction would still be
> about the same speed than what we have now. I haven't seen anybody
> working on swapping out the current algorithm. And I don't really see
> a reason to, it would introduce a load of headaches for no real gain.

Uh, I am confused.  I thought you said we were leaving some performance
on the table.  What is that?   I though CRC32 was SSE4.1.  Why is CRC32
good for the WAL but bad for the page checksums?  What about the WAL
page images?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +