Christian Ziech created LUCENE-8219:
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Summary: LevenshteinAutomata should estimate the number of states
and transitions
Key: LUCENE-8219
URL: https://issues.apache.org/jira/browse/LUCENE-8219
Project: Lucene - Core
Issue Type: Improvement
Reporter: Christian Ziech
Currently the toAutomaton() method of the LevenshteinAutomata class uses the
default constructor of the Automaton although it exactly knows how many states
the automaton will have and can do a reasonable estimation on how many
transitions it will need as well.
I suggest changing the lines {code:language=java|firstline=154|linenumbers=true}
// the number of states is based on the length of the word and n
int numStates = description.size();
Automaton a = new Automaton();
int lastState;
{code}
to
{code:language=java|firstline=154|linenumbers=true}
// the number of states is based on the length of the word and n
final int numStates = description.size();
final int numTransitions = numStates * Math.min(1 + 2 * n, alphabet.length);
final int prefixStates = prefix != null ? prefix.codePointCount(0,
prefix.length()) : 0;
final Automaton a = new Automaton(numStates + prefixStates, numTransitions);
int lastState;
{code}
For my test data this cut down on the total amount of memory needed for int
arrays by factor 4. The estimation of "1 + 2 * editDistance" should maybe
rather be replaced by a value coming from the ParametricDescription used.
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