Re: How much do the hint bits help?

On Wed, Dec 22, 2010 at 11:06 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Merlin Moncure <mmoncure@gmail.com> writes:
>> well, simon's point that hint bits complicate checksum may nor may not
>> be the case, but no hint bits = less i/o = less checksumming (unless
>> you checksum around the hint bits).
>
> I think you're optimistically assuming the extra clog accesses don't
> cost any I/O.

right, but clog is much more highly packed which is both a good and a
bad thing.  my conjecture here is that jamming the clog files is
actually good, because that keeps them 'hot' and more than compensates
the extra heap i/o.  the extra lock of course is scary.

here's the thing, compared to the 90's when they were put in, the
transaction space has shrunk by half and we put gigabytes, not
megabytes of memory into servers.  what does this mean for the clog?
that's what i'm after.

merlin