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https://issues.apache.org/jira/browse/LUCENE-9981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17353964#comment-17353964
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Ori D commented on LUCENE-9981:
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[~rcmuir],
We don't expose the entire elasticsearch DSL of course.
We do require authentication.
But the business needs also requires us to allow users for specifying regexp
and then we perform some kind of a regexp query in elastiscearch with that
regexp.
It's not exactly like any other slow query, because we control our queries
(through API layer) and our data. However, in this specific case, the user may
provide a "malicious" regexp that can cause high CPU.
It's true that the best solution is to simply avoid any regexp coming from
end-users. However, this is not aligned with our business needs at the moment.
We can find several ways to mitigate or minimize this possibility of High CPU
(for example, don't allow regexp with '{}' ). But I prefer having a solid
solution integrated into the elasticsearch engine.
I hope I was able to explain it better.
Please consider some fix to 8.x - even a simple one like you originally
suggested of a 1-liner patch - so we can enjoy the fix in the near future.
Thanks,
Ori.
> 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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