Re: COMMIT NOWAIT Performance Option

Gregory Stark wrote:
> "Jonah H. Harris" <jonah.harris@gmail.com> writes:
> 
>> This proposed design is overcomplicated and a waste of space.  I mean,
>> we reduce storage overhead using phantom command id and variable
>> varlena, but let's just fill it up again with unnecessary junk bytes.
> 
> We reduced storage overhead using phantom command id by 8 bytes *per tuple*. I
> hardly think 8 bytes per page is much of a concern. You're already losing an
> average of 1/2 a tuple per page to rounding and that's a minimum of 16 bytes
> for the narrowest of tuples.
> 
>>> That seems pretty unlikely. CRC checks are expensive cpu-wise, we're already
>>> suffering a copy due to our use of read/write the difference between
>>> read/write of 8192 bytes and readv/writev of 511b*16+1*6 is going to be
>>> non-zero but very small. Thousands of times quicker than the CRC.
>> Prove it.
> 
> We've already seen wal CRC checking show up at the top of profiles.

yeah - on fast boxes (diskio wise) wal-crc checking is nearly always on 
the very top of wal-intensive workloads.


Stefan