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Re: Extended globbing seems to have become much slower in recent versions of Zsh

On Fri, 04 Mar 2016 14:22:23 +0100
Jesper Nygårds <jesper.nygards@xxxxxxxxx> wrote:
> I don't know if this is relevant, but I have some more findings. I wanted
> to know which sub directory was contributing the most to the amount of time
> taken to process the root directory. I then realized that the sum of the
> time it took to process each sub directory separately was much lower than
> processing the whole root directory at once. In the run below, you can see
> that whilst it takes about 36 seconds to process the root directory, it
> only takes about 13 seconds to process all directories one at a time.
> Furthermore, when I descend into the sub directory taking the longest time
> in the first run, and run all its sub directories in sequence, the sum of
> these sub-sub directories is significantly lower than for the whole sub
> directory. So obviously the processing time is not linear with the number
> of files.

You'd think that would point towards something higher level than the
pattern matching itself, anyway.  Brainstorming [this is a euphemism for
I haven't the first clue what I'm talking about]...

- Memory management associated with multiple directories; could be
allocation or heap management.

- Poor structuring of globbing code meaning it's repeating operations,
i.e. it's not walking trees in a sensible fashion.

- Some auxiliary operation associated with the file tree that's
giving a similar effect to the foregoing (i.e. we walk the tree itself OK
but then repeat some associated operation that should be cached).

- Some form of context switching problem [now it's really getting silly]

Most of these guesses ought to be amenable to tracing through some sort
of profiling suite.  Even some fprintfs to check what directories we've
handled at what point might help.


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