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Re: About performance, hash-tables and garbage collection
From: |
Oliver Scholz |
Subject: |
Re: About performance, hash-tables and garbage collection |
Date: |
Sat, 21 Sep 2002 01:09:13 +0200 |
User-agent: |
Gnus/5.090008 (Oort Gnus v0.08) Emacs/21.2 (i686-pc-linux-gnu) |
"Stefan Monnier <foo@acm.com>" <monnier+gnu.emacs.help/news/@flint.cs.yale.edu>
writes:
>> 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))))
>
> The `if' overhead will probably dwarf the difference, so I'd say,
> just use the hash-table. Most likely any performance problem you'll have
> won't come from that anyway.
Thank you. That helps.
>> 2. I noticed that the garbage collector hits in a little bit too often,
>
> What's too often ? Why do you care ?
[...]
Well, I changed my mind. The ugliness/performance ratio of any attempt
to squeeze a little bit more out of that inner loop is very likely too
bad. So I do not care about a few garbage collections anymore.
-- Oliver
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