Message-ID: <47EB98EA.7020402@dunslane.net>
Date: Thu, 27 Mar 2008 08:54:02 -0400
From: Andrew Dunstan <andrew@dunslane.net>
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To: "Zubkovsky, Sergey" <Sergey.Zubkovsky@transas.com>
CC: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@commandprompt.com>,
	Gregory Stark <stark@enterprisedb.com>, pgsql-hackers@postgresql.org,
	Magnus Hagander <magnus@hagander.net>
Subject: Re: [DOCS] pg_total_relation_size() and CHECKPOINT
References: <528853D3C5ED2C4AA8990B504BA7FB850106DF2A@sol.transas.com>
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Zubkovsky, Sergey wrote:
> Maybe this helps:
>
> "It is not an error to set a file pointer to a position beyond the end
> of the file. The size of the file does not increase until you call the
> SetEndOfFile, WriteFile, or WriteFileEx function. A write operation
> increases the size of the file to the file pointer position plus the
> size of the buffer written, which results in the intervening bytes
> uninitialized."
>
> http://msdn2.microsoft.com/en-us/library/aa365541(VS.85).aspx
>
> According to Windows' lseek implementation (attached) SetEndOfFile()
> isn't called for this case.
>
>   
>

Yes, but we immediately follow the lseek bye a write(). See 
src/backend/storage/smgr/md.c:mdextend() .

cheers

andrew