About performance, hash-tables and garbage collection

[Oliver Scholz <alkibiades@gmx.de>]

I am currently writing a library in which the main function has an
inner loop that may run several thousand times. So I care a bit about
the performance of this inner loop.

1. I have read that hash-tables have a little overhead and that
   association lists are a little bit faster, when they contain not
   more than about a dozen of key-value pairs. It is _possible_ that I
   have to maintain several hundreds or thousand of key/value pairs,
   but in most cases it will be only a dozen or so. So my question is:
   how much overhead has a hashtable? Makes it sense to add a
   condition, like this:

   (if (> ncolours 15) 
       (gethash colour colour-map) 
     (cdr (assoc (colour colour-map))))   

2. I noticed that the garbage collector hits in a little bit too
   often, though I do not know why. I have a lot of `setq'-statements
   like `(setq pointer (1+ pointer))'. Is it possible that they are
   the cause? If so, what could I do?

    -- Oliver

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