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https://issues.apache.org/jira/browse/LUCENE-2933?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12997318#comment-12997318
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Dawid Weiss commented on LUCENE-2933:
-------------------------------------
Thanks Uwe!
> Two-stage state expansion for the FST: distance-from-root and child-count
> criteria.
> -----------------------------------------------------------------------------------
>
> Key: LUCENE-2933
> URL: https://issues.apache.org/jira/browse/LUCENE-2933
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Dawid Weiss
> Priority: Trivial
> Fix For: 4.0
>
>
> In the current implementation FST states are expanded into a binary search on
> labels (from a vector of transitions) when the child count of a state exceeds
> a given predefined threshold (NUM_ARCS_FIXED_ARRAY). This threshold affects
> automaton size and traversal speed (as it turns out when benchmarked). For
> some degenerate (?) data sets, close-to-the-root nodes could have a small
> number of children (below the threshold) and yet be traversed on every single
> seek.
> A fix of this is to introduce two control thresholds:
> EXPAND state if (distance-from-root <= MIN_DISTANCE || children-count >=
> NUM_ARCS_FIXED_ARRAY)
> My plan is to create a data set that will prove this first and then to
> implement the workaround above.
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