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https://issues.apache.org/jira/browse/LUCENE-2967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13007031#comment-13007031
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Michael McCandless commented on LUCENE-2967:
--------------------------------------------
Hmm, unfortunately, I'm seeing the patch make FST building slower, at
least in my env/test set. I built FST for the 38M wikipedia terms.
I ran 6 times each, alternating trunk & patch.
I also turned off saving the FST, and ran -noverify, so I'm only
measuring time to build it. I run java -Xmx2g -Xms2g -Xbatch, and
measure wall clock time.
Times on trunk (seconds):
{noformat}
43.795
43.493
44.343
44.045
43.645
43.846
{noformat}
Times w/ patch:
{noformat}
46.595
47.751
47.901
47.901
47.901
47.700
{noformat}
We could also try less generous load factors...
> Use linear probing with an additional good bit avalanching function in FST's
> NodeHash.
> --------------------------------------------------------------------------------------
>
> Key: LUCENE-2967
> URL: https://issues.apache.org/jira/browse/LUCENE-2967
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Dawid Weiss
> Assignee: Dawid Weiss
> Priority: Trivial
> Fix For: 4.0
>
> Attachments: LUCENE-2967.patch
>
>
> I recently had an interesting discussion with Sebastiano Vigna (fastutil),
> who suggested that linear probing, given a hash mixing function with good
> avalanche properties, is a way better method of constructing lookups in
> associative arrays compared to quadratic probing. Indeed, with linear probing
> you can implement removals from a hash map without removed slot markers and
> linear probing has nice properties with respect to modern CPUs (caches). I've
> reimplemented HPPC's hash maps to use linear probing and we observed a nice
> speedup (the same applies for fastutils of course).
> This patch changes NodeHash's implementation to use linear probing. The code
> is a bit simpler (I think :). I also moved the load factor to a constant --
> 0.5 seems like a generous load factor, especially if we allow large FSTs to
> be built. I don't see any significant speedup in constructing large automata,
> but there is no slowdown either (I checked on one machine only for now, but
> will verify on other machines too).
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