Re: patch review : Add ability to constrain backend temporary file space

On 03/06/11 12:33, Cédric Villemain wrote:
> 2011/6/2 Mark Kirkwood<mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>:
>> On 01/06/11 09:24, Cédric Villemain wrote:
>>> * I am not sure it is better to add a fileSize like you did or use
>>> relationgetnumberofblock() when file is about to be truncated or
>>> unlinked, this way the seekPos should be enough to increase the global
>>> counter.
>>>
>> The temp files are not relations so I'd have to call stat I guess. Now
>> truncate/unlink can happen quite a lot (e.g hash with many files) and I
>> wanted to avoid adding too many library calls to this code for performance
>> reasons, so on balance I'm thinking it is gonna be more efficient to
>> remember the size in the Vfd.
> I am not sure temporary relation are truncated. I have not checked
> right now, but IIRC, we don't need to truncate it. And I believe it
> would defeat the log_temp feature because log_temp is done on
> FileClose() only.
>
> If we are to add a field in struct vfd to keep the filesize then some
> optimization may happens for logging too....

We pretty much need to store the file size I think, due to needing to
work out if FileWrite is re-writing inside the file or extending it. So
maybe we could avoid a stat on unlink too (mind you it is a nice
validity check that the ongoing size accounting is correct). I was/am
keen to avoid changing too much here (heh - maybe I'm being too timid...).

Cheers

Mark