Horton

Re: How much do the hint bits help?

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Aidan Van Dyk <aidan@highrise.ca>, Simon Riggs <simon@2ndquadrant.com>, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2010-12-22T20:08:01Z
Lists: pgsql-hackers 
On 22.12.2010 18:12, Merlin Moncure wrote:
> 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.

As a sidenote: note that the clog is not currently CRC'd.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com