[evs] Current status

Tony Hoyle tony.hoyle at march-hare.local
Mon Jan 15 02:12:18 GMT 2007

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Kelly F. Hickel wrote:
> Note that with the patch disk IO is up considerably, percentage wise, so
> there's some lower limit where finding the rev faster isn't going to
> help, compared to writing the tags in the files, but I'm sure we aren't
> there yet.

Someone came up with a patch that avoided this but I never applied it - 
they preallocated lots of space in the RCS files then wrote the new 
patches directly into the existing file, avoiding the rewrite entirely.

For their case where they were doing lots of tagging for builds etc. it 
was quite a large speedup.  The downside (which unfortunately meant I 
never applied it) was you lost crash resilience - a badly timed crash 
could corrupt the tag data.

Finding the largest tag number *should* be an entirely in-memory 
operation, once RCS_parsercsfile is has been called (and it will be... 
theoretically you could optimise it out but it'd be a lot of work), 
since the version numbers and various bits of information are already 
cached.   You just have to iterate through the relevant ones and find 
the largest ones.

.. or just forget about all that and have a 'largest tagid' written into 
the RCS file header and increment it.  Then it's a single operation to 
read it and effectively zero time to calculate the new one.  I could add 
that into evs in about 5 minutes if there was a measurable benefit (TBH 
I'd prefer to get the numbers from a profiler first to find the critical 

btw. what takes 12 minutes.. the entire repository?  How many files?


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