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Message-ID: <02c101c31e3e$7ffdc910$78d96f83@pomello>
From: "Max Bowsher" <maxb AT ukf DOT net>
To: "Pierre A. Humblet" <pierre DOT humblet AT ieee DOT org>, <cygwin AT cygwin DOT com>
References: <Law10-F79o4cWScPAA600033a95 AT hotmail DOT com> <028f01c31e38$0e428c30$78d96f83 AT pomello> <20030519200848 DOT GA246379 AT Worldnet>
Subject: Re: SPARSE files considered harmful - please revert
Date: Mon, 19 May 2003 20:40:27 +0100
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Pierre A. Humblet wrote:
> On Mon, May 19, 2003 at 07:54:19PM +0100, Max Bowsher wrote:
>> John Vincent wrote:
>>>
>>> I looked up sparse files on MSDN and found the following link:
>>>
>>>
>>
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/sparse_file_operations.asp
>>>
>>> The most interesting thing is that a sparse file is only sparse if the
>> zeros
>>> in the file are written with a special operation. I strongly suspect
that
>>> the patch to support sparse files introduced in cygwin is incorrect (or
at
>>> least incomplete)
>>
>> Areas that are simply seeked over, and never written to, should be sparse
as
>> well.
>
> Not only they "should be", they are.
>
>> Anyway:
>>
>> Based on the posted numbers, global use of sparse files is a bad idea.
Can
>> we conditionalize sparse files on a $CYGWIN option? (Or something else, I
>> don't mind, but the important thing is that it should not be on by
default.)
>
> Why not make in on by default *when it can help*, i.e. when the write()
> leaves holes?

Does anyone know of any programs which write non-sparse files, but not
contiguously? If there are none, then this approach should be fine.

In any case, the $CYGWIN approach could be a valid temporary measure until
someone writes the heuristic code.


Max.


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