From: | Zdenek Kotala <Zdenek(dot)Kotala(at)Sun(dot)COM> |
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To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Is mdextend really safe? |
Date: | 2008-08-20 11:20:51 |
Message-ID: | 48ABFE13.3010006@sun.com |
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Thread: | |
Lists: | pgsql-hackers |
Gregory Stark napsal(a):
> On Unix that creates a sparse file where the intervening blocks are not
> allocated. When we later write out those blocks the filesystem then has to
> allocate space for them. IIRC the bug reports were from Windows. I'm not sure
> what NTFS's behaviour with sparse files is.
NTFS has sparse file feature, but how it works ...
> Now this only matters if we ever call mdextend on a block which isn't the
> block immediately following the end of file. Is that true?
I think, that it could happens only during wal log replay, but at the
end everything should be OK. Look into ReadBuffer_common there is
following code:
00226 /* Substitute proper block number if caller asked for P_NEW */
00227 if (isExtend)
00228 blockNum = smgrnblocks(smgr, forkNum);
Zdenek
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