Thomas Poppe created LUCENE-8102:
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Summary: CompiledAutomaton performance for determining common
suffix
Key: LUCENE-8102
URL: https://issues.apache.org/jira/browse/LUCENE-8102
Project: Lucene - Core
Issue Type: Improvement
Components: core/FSTs
Affects Versions: 7.1
Reporter: Thomas Poppe
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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