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  1. Lucene - Core
  2. LUCENE-8102

CompiledAutomaton performance for determining common suffix

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    Details

    • Type: Improvement
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 7.1
    • Fix Version/s: None
    • Component/s: core/FSTs
    • Labels:
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    • Lucene Fields:
      New

      Description

      We're using the automaton package as part of Elasticsearch for doing regexp queries. Our business requires us to process rather complex regular expressions, for example (we have more complex examples, but this one illustrates the problem):

              (¦.)*(¦?[^¦]){1,10}ab(¦.)*(¦?[^¦]){1,10}c(¦.)*(¦?[^¦]){1,10}d
      

      With a large enough value of maxDeterminizedStates, this works. The problem we're having is that the conversion of this regular expression to a CompiledAutomaton takes very long. Almost all of the time goes into determining the common suffix for the Automaton (which is "d" in this example) - calculated with a call to Operations.getCommonSuffixBytesRef.

      This suffix is only used as an optimization. Skipping the calculation of this suffix allows us to process these kinds of queries.

      • Would it be possible to introduce a way to skip the calculation of this common suffix (ideally something we control from within our query to Elasticsearch)?
      • Or would it be possible to take a look at this getCommonSuffixBytesRef operation, to see if it can be optimized? Most of the time goes to determinizing the reversed automaton - maybe this can be avoided somehow?

      Reaction from Mike McCandless on the mailing list:
      This is just an optimization; maybe we should expose an option to disable it?
      Or maybe we can find the common suffix on an NFA instead, to avoid determinization?

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            • Assignee:
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              Reporter:
              ThomasPoppe Thomas Poppe
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              • Created:
                Updated: