Re: offset-based hash table for ASCII data

From:
Robert Klemme <shortcutter@googlemail.com>
Newsgroups:
comp.unix.programmer,comp.lang.java.programmer,comp.programming
Date:
Sun, 27 Apr 2008 12:11:55 +0200
Message-ID:
<67j1rdF2o8htsU1@mid.individual.net>
On 25.04.2008 18:05, Rex Mottram wrote:

Rex Mottram wrote:

Thanks again. And please let us know the outcome (aka speed
improvement) or any issues you find along the way. That way we can
all learn a bit. :-)


Will do.


As promised, the final results:


Thank you for the summary!

A. I've had no problems with CDB in either of the versions I'm using; it
works quite well, is clearly documented, etc. It took a few minutes to
port TinyCDB to Windows but no big deal, and I've offered the diffs to
the author.


Thank you, that way the community can benefit as well.

B. In the particular test case I was profiling, a typical run of the XML
version averaged around 19-20 minutes. The CDB version is around *2*
minutes. I consider this a rousing success.


Indeed!

I was a little surprised, FWIW, to find that the CDB file was typically
no smaller than the XML file. Given how "wordy" XML is I'd have expected
almost any other format to be smaller, but CDB came in around the same
size. Of course these details will vary considerably with many factors
so this is just one data point.


IIRC CDB uses hashing. At least in memory hash tables are usually
larger than the number of entries in there so that might be the case
here as well. I am sure a closer look at the documentation of the file
format will reveal the reason but since you said that bandwidth was not
an issue I guess it's not worthwhile bothering. Still a good hint for
others.

Kind regards

    robert

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