Re: How much do the hint bits help?

On Wed, Dec 22, 2010 at 11:12 AM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Wed, Dec 22, 2010 at 11:06 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Merlin Moncure <mmoncure(at)gmail(dot)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.

er, should have said, plus less heap i/o compensates the extra clog i/o.

merlin