Re: [HACKERS] wal_checksum = on (default) | off

> > Ok, so when you need CRC's on a replicate (but not on the master)
you
> > turn it
> > off during standby replay, but turn it on when you start the
replicate
> > for normal operation.
>
> Thought: even when it's off, the CRC had better be computed for
> shutdown-checkpoint records. Else there's no way to turn it on even
> with a postmaster restart --- unless we accept the idea of poking a
hole
> in the normal mode. (Which I still dislike, and even more so if the
> special value is zero. Almost any other value would be safer than
zero.)
>
> On the whole, though, I still don't want to put this in. I don't
think
> Simon has thought it through sufficiently,

Well, the part that we do not really want a special value (at least not
0)
is new, and makes things a bit more complicated.

> and we haven't even seen any demonstration of a big speedup.

Yes, iirc the demonstration was with the 64 bit crc instead of the
sufficient
32-bit (or a bad crc compiler optimization?).
But I do think it can be shown to provide significant speedup
(at least peak burst performance).

Especially on target hardware WAL write IO is extremely fast
(since it is write cached), so the CPU should show.

Andreas