Re: How much do the hint bits help?

On 23/12/10 10:54, Tom Lane wrote:
> Josh Berkus<josh@agliodbs.com>  writes:
>> Regarding the contention which Tom expects: the extra load on the CLOG
>> would be 100% reads, no?  If it's *all* reads, why would we have any
>> more contention than we have now?
> Read involves sharelock which still causes contention.  Those bufmgr
> contention storms we saw before were completely independent of whether
> the pages were accessed for read or for write.
>
> Another thing to keep in mind is that the current clog access code is
> designed on the assumption that there's considerable locality of access
> to pg_clog, ie, you usually only need to consult it for recent XIDs
> because older ones have been hinted.  Turn off hint bits, that behavior
> goes out the window.

Would a larger (or configurable) clog cache help with this tho?

Cheers

Mark