[TSVN] Yet more shell optimisation

Hi all,

I'm still looking at shell extension optimisation, largely still running
very aggressive tests on IsMemberOf.

Now that all the big things are done, it's still apparent that the
PathIsDirectory call in IsMemberOf is expensive. (According to DPP, about
20% of the time in a test where I read the (cached) status of a pair of
files 20000 times each).

As an experiment, I made a separate member in SVNFolderStatus called
'GetCachedItem', which took *only* a path argument. This function just
contains the m_cache.find() code from GetFullStatus, and it returns a
status pointer if it finds the entry in the cache, or NULL if it doesn't.

I call this in IsMemberOf *before* the PathIsDirectory - if it returns
null, then I proceed with the usual stuff. If it finds a cache hit, then I
just use that value, and skip all the usual content of IsMemberOf.

So in role and position it's just like the single file 'mini-cache' test,
but instead it's searching the full cache.

Before running the stress test, I pre-loaded the cache by getting the
status on a folder - the cache had 80 items in, which is probably not
unrepresentative.

This turns out to be *enormously* faster. My test run reduced from about
1100ms to about 180ms, merely through avoiding 40000 calls to PathIsDirectory.
(Not sure how this squares with DPP's 20%, but it's definitely removing
PathIsDirectory which makes the difference - putting a dummy call to it in
restored the run time to around 1100ms.)

It feels that this would be worthwhile - even if the cache was a lot
bigger, I don't think its lookup time would rise significantly - std::map
lookups are O(log(n)) anyway.

Cheers,

Will

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Received on Tue Nov 2 13:56:55 2004