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Re: Block-level CRC checks

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
Cc: Aidan Van Dyk <aidan(at)highrise(dot)ca>, 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 17:07:31
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Jonah H. Harris wrote:
> PG doesn't care because during hint-bits aren't logged and during
> normal WAL replay, the old page will be pulled from the WAL.  I
> believe what Tom is referring to is that the buffer PG sends to
> write() can still be modified by way of SetHintBits between the time
> smgrwrite is called and the time the actual write takes place, which
> is why we can't rely on a checksum of the buffer pointer passed to
> smgrwrite and friends.
> If we're double-buffering the write, I don't see where we could be
> introducing a torn-page, as we'd actually be writing a copied version
> of the buffer.  Will look into this.

The torn page is during kernel write to disk, I assume, so it is still

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + If your life is a hard drive, Christ can be your backup. +

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