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https://issues.apache.org/jira/browse/LUCENE-9981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17353970#comment-17353970
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Michael McCandless commented on LUCENE-9981:
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{quote}We can add a simple note to {{MIGRATE.TXT}} to make it even easier?
{quote}
+1, I'll add that!
Re: 8.x, I agree it would be nice to backport some fix there. We could at least
backport [~rcmuir]'s awesome improvement to
{{Operations.getCommonPrefix/Suffix}} – that is a smallish API break (no longer
takes the {{int maxDeterminizedStates}}) on a low-level Automaton utility API.
I'm not sure how to correctly/safely backport the switch to measuring "effort
spent", instead of eventual state count, during determinize. Maybe we leave
the {{int}} parameter, but use some heuristic to translate that to "effort"
inside the method? The upside of that is there is no API break, but the
downside is, the thrown exception is misleading/confusing, though we could just
fix the wording of the exception message to indicate that this parameter now
means "effort"? Or, perhaps {{int}} is enough bits and we shouldn't even make
the API break in {{main}} either?
> CompiledAutomaton.getCommonSuffix can be extraordinarily slow, even with
> default maxDeterminizedStates limit
> ------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-9981
> URL: https://issues.apache.org/jira/browse/LUCENE-9981
> Project: Lucene - Core
> Issue Type: Task
> Reporter: Robert Muir
> Priority: Major
> Attachments: LUCENE-9981.patch, LUCENE-9981.patch, LUCENE-9981.patch,
> LUCENE-9981_nfaprefix.patch, LUCENE-9981_test.patch,
> three-repeats-reverse-det.png, three-repeats.png
>
>
> We have a {{maxDeterminizedStates = 10000}} limit designed to keep
> regexp-type queries from blowing up.
> But we have an adversary that will run for 268s on my laptop before hitting
> exception, first reported here:
> https://github.com/opensearch-project/OpenSearch/issues/687
> When I run the test and jstack the threads, this what I see:
> {noformat}
> "TEST-TestOpensearch687.testInteresting-seed#[4B9C20A027A9850C]" #15 prio=5
> os_prio=0 cpu=56960.04ms elapsed=57.49s tid=0x00007fff7006ca80 nid=0x231c8
> runnable [0x00007fff8b7f0000]
> java.lang.Thread.State: RUNNABLE
> at
> org.apache.lucene.util.automaton.SortedIntSet.decr(SortedIntSet.java:106)
> at
> org.apache.lucene.util.automaton.Operations.determinize(Operations.java:769)
> at
> org.apache.lucene.util.automaton.Operations.getCommonSuffixBytesRef(Operations.java:1155)
> at
> org.apache.lucene.util.automaton.CompiledAutomaton.<init>(CompiledAutomaton.java:247)
> at
> org.apache.lucene.search.AutomatonQuery.<init>(AutomatonQuery.java:104)
> at
> org.apache.lucene.search.AutomatonQuery.<init>(AutomatonQuery.java:82)
> at org.apache.lucene.search.RegexpQuery.<init>(RegexpQuery.java:138)
> at org.apache.lucene.search.RegexpQuery.<init>(RegexpQuery.java:114)
> at org.apache.lucene.search.RegexpQuery.<init>(RegexpQuery.java:72)
> at org.apache.lucene.search.RegexpQuery.<init>(RegexpQuery.java:62)
> at
> org.apache.lucene.TestOpensearch687.testInteresting(TestOpensearch687.java:42)
> {noformat}
> This is really sad, as {{getCommonSuffixBytesRef()}} is only supposed to be
> an "up-front" optimization to make the actual subsequent terms-intensive part
> of the query faster. But it makes the whole query run for nearly 5 minutes
> before it does anything.
> So I definitely think we should improve {{getCommonSuffixBytesRef}} to be
> more "best-effort". For example, it can reduce the lower bound to {{1000}}
> and catch the exception like such:
> {code}
> try {
> // this is slow, and just an opto anyway, so don't burn cycles on it for
> some crazy worst-case.
> // if we don't set this common suffix, the query will just run a bit
> slower, that's all.
> int limit = Math.min(1000, maxDeterminizedStates);
> BytesRef suffix = Operations.getCommonSuffixBytesRef(binary, limit);
> ... (setting commonSuffixRef)
> } catch (TooComplexTooDeterminizeException notWorthIt) {
> commonSuffixRef = null;
> }
> {code}
> Another, maybe simpler option, is to just check that input state/transitions
> accounts don't exceed some low limit N.
> Basically this opto is geared at stuff like leading wildcard query of "*foo".
> By computing that the common suffix is "foo" we can spend less CPU in the
> terms dictionary because we can first do a memcmp before having to run data
> thru any finite state machine. It's really a microopt and we shouldn't be
> spending whole seconds of cpu on it, ever.
> But I still don't quite understand how the current limits are giving the
> behavior today, maybe there is a bigger issue and I don't want to shove
> something under the rug.
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