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Re: Torn page hazard in ginRedoUpdateMetapage()

From: Daniel Farina <daniel(at)heroku(dot)com>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Torn page hazard in ginRedoUpdateMetapage()
Date: 2012-05-03 04:01:49
Message-ID: CAAZKuFa784ZWuQmqg9h5b55qj1+X_rghA0PHB4_tFoqXjQxHNA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, May 2, 2012 at 6:06 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> Can we indeed assume that all support-worthy filesystems align the start of
> every file to a physical sector?  I know little about modern filesystem
> design, but these references leave me wary of that assumption:
>
> http://www.mail-archive.com/linux-btrfs(at)vger(dot)kernel(dot)org/msg14690.html
> http://en.wikipedia.org/wiki/Block_suballocation
>
> If it is a safe assumption, we could exploit it elsewhere.

Not to say whether this is safe or not, but it *is* exploited
elsewhere, as I understand it: the pg_control information, whose
justification for its safety is its small size.  That may point to a
very rare problem with pg_control rather the safety of the assumption
it makes.

-- 
fdr

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