Two-stage state expansion for the FST: distance-from-root and child-count
criteria.
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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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