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Re: [RFC] A libsvn_wc properties optimisation

From: Gareth McCaughan <gareth.mccaughan_at_pobox.com>
Date: 2004-11-09 01:27:44 CET

On Saturday 06 November 2004 14:28, Philip Martin wrote:
> Barry Scott <barry@barrys-emacs.org> writes:
> > The win is that you only have to do a file open on one file rather
> > then lots of files/directory. I'm sure that parsing one file is far
> > faster then open 10 files. The file sizes are trivial. I have 1856
> > bytes for 54 files in my repo for example.
>
> The "I don't have any large properties, why should anyone else?"
> argument, that came up last time as well.
>
> Suppose one of the files has a 1MB property, now every operation that
> reads properties on any file now has to read that all that data.

So, a file's entries in the props file can optionally indicate
that the properties are stored in a separate per-file props file.
When a file gets a 1MB property, or when it gets large numbers
of properties, you switch to using the per-file props file. If the
big properties go away, you switch back. With some hysteresis
to avoid the obvious thrashing problem. ("You", of course,
means the WC library.)

That's more complicated than either "always use a single
file" or "always use separate files", but it's still fairly simple
and gives you decent performance in the common case
without screwing you in the worst case.

-- 
g
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Received on Tue Nov 9 01:28:09 2004

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