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Posted to issues@lucene.apache.org by "Michael McCandless (Jira)" <ji...@apache.org> on 2021/09/29 12:19:00 UTC
[jira] [Commented] (LUCENE-9983) Stop sorting determinize powersets
unnecessarily
[ https://issues.apache.org/jira/browse/LUCENE-9983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17422088#comment-17422088 ]
Michael McCandless commented on LUCENE-9983:
--------------------------------------------
[~zhai7631] I think this can be resolved now?
> Stop sorting determinize powersets unnecessarily
> ------------------------------------------------
>
> Key: LUCENE-9983
> URL: https://issues.apache.org/jira/browse/LUCENE-9983
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael McCandless
> Priority: Major
> Time Spent: 5h 40m
> Remaining Estimate: 0h
>
> Spinoff from LUCENE-9981.
> Today, our {{Operations.determinize}} implementation builds powersets of all subsets of NFA states that "belong" in the same determinized state, using [this algorithm|https://en.wikipedia.org/wiki/Powerset_construction].
> To hold each powerset, we use a malleable {{SortedIntSet}} and periodically freeze it to a {{FrozenIntSet}}, also sorted. We pay a high price to keep these growing maps of int key, int value sorted by key, e.g. upgrading to a {{TreeMap}} once the map is large enough (> 30 entries).
> But I think sorting is entirely unnecessary here! Really all we need is the ability to add/delete keys from the map, and hashCode / equals (by key only – ignoring value!), and to freeze the map (a small optimization that we could skip initially). We only use these maps to lookup in the (growing) determinized automaton whether this powerset has already been seen.
> Maybe we could simply poach the {{IntIntScatterMap}} implementation from [HPPC|https://github.com/carrotsearch/hppc]? And then change its {{hashCode}}/{{equals }}to only use keys (not values).
> This change should be a big speedup for the kinds of (admittedly adversarial) regexps we saw on LUCENE-9981.
>
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