| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: How much do the hint bits help? |
| Date: | 2010-12-22 20:08:01 |
| Message-ID: | 4D125AA1.8050602@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 22.12.2010 18:12, Merlin Moncure 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.
As a sidenote: note that the clog is not currently CRC'd.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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