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https://issues.apache.org/jira/browse/LUCENE-9981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17355256#comment-17355256
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Nick Knize commented on LUCENE-9981:
------------------------------------
bq. Even with no API break, I don't want these changes rushed in to meet some
arbitrary 8.9 deadline, I'm really concerned about that.
+1 for letting this bake in main. Consumers of the API should handle the lack
of auth separately from the fix. Many thanks to [~rmuir] and [~mikemccand] for
the hard work on this.
> 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.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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