From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | decibel <decibel(at)decibel(dot)org>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, jd(at)commandprompt(dot)com, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Block-level CRC checks |
Date: | 2009-12-04 12:54:51 |
Message-ID: | 200912041254.nB4Cspj02484@momjian.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Fri, 2009-12-04 at 07:12 -0500, Bruce Momjian wrote:
>
> > I think the hint bit has to be added to the item pointer, by using the
> > offset bits that are already zero, according to Greg Stark. That
> > solution leads to easy programming, no expanding hint bit array, and it
> > is backward compatible so doesn't cause problems for pg_migrator.
>
> Seems like a reasonable way forward.
>
> As I pointed out here
> http://archives.postgresql.org/pgsql-hackers/2009-12/msg00056.php
> we only need to use 3 bits not 4, but it does limit tuple length to 4096
> for all block sizes. (Two different options there for doing that).
>
> An added advantage of this approach is that the cachelines for the item
> pointer array will already be in CPU cache, so there is no additional
> access time when we set the hint bits when they are moved to their new
> position.
>
> I should also point out that removing 4 bits from the tuple header would
> allow us to get rid of t_infomask2, reducing tuple length by a further 2
> bytes.
Wow, that is a nice win. Does alignment allow us to actually use that
space?
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
From | Date | Subject | |
---|---|---|---|
Next Message | Simon Riggs | 2009-12-04 12:57:05 | Re: Block-level CRC checks |
Previous Message | Alvaro Herrera | 2009-12-04 12:52:00 | Re: Block-level CRC checks |