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Re: Block-level CRC checks

From: Aidan Van Dyk <aidan(at)highrise(dot)ca>
To: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>,Brian Hurt <bhurt(at)janestcapital(dot)com>,Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-02 16:51:01
Message-ID: 20081002165101.GZ16893@yugib.highrise.ca (view raw or flat)
Thread:
Lists: pgsql-hackers
* Jonah H. Harris <jonah(dot)harris(at)gmail(dot)com> [081002 12:43]:
 
> > #define write(fd, buf, count) buffer_crc_write(fd, buf, count)
> 
> I certainly wouldn't interpose the write() call itself; that's just
> asking for trouble.

Of course not, that was only to show that whatever you currenlty pritect
"write()" with, is valid for protecting the buffer+write.

> > But I thought you didn't really care about hint-bit updates, even in the
> > current strategy... but I'm fully ignorant about the code, sorry...
> 
> The current implementation does not take it into account.

So if PG currently doesn't care about the hit-bits being updated, during
the write, then why should introducing a double-buffer introduce the a
torn-page problem Tom mentions?  I admit, I'm fishing for information
from those in the know, because I haven't been looking at the code long
enough (or all of it enough) to to know all the ins-and-outs...

a.
-- 
Aidan Van Dyk                                             Create like a god,
aidan(at)highrise(dot)ca                                       command like a king,
http://www.highrise.ca/                                   work like a slave.

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