Re: Set hint bits upon eviction from BufMgr

On Fri, Mar 25, 2011 at 3:32 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> On 25.03.2011 16:52, Merlin Moncure wrote:
>>
>> Without this bit, the only way to set hint bits going during bufmgr
>> eviction is to do a visibility check on every tuple, which would
>> probably be prohibitively expensive.
>
> I don't think the naive approach of scanning all tuples would be too bad,
> actually. The hint bits only need to be set once, and it'd be bgwriter
> shouldering the overhead.

I was thinking the same thing. The only thing I'm worried about is
whether it'd make the bgwriter less responsive; we already have some
issues in that department.

> The problem with setting hing bits when a buffer is evicted is that it
> doesn't help with the bulk load case. The hint bits can't be set for a bulk
> load until the load is finished and the transaction commits.
>
> Maybe it would still be worthwhile to have bgwriter set hint bits, to reduce
> I/O caused by hint bit updates in an OLTP workload, but that's not what
> people usually complain about.

Yeah.

--
Robert Haas
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