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https://issues.apache.org/jira/browse/LUCENE-5584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13967591#comment-13967591
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Robert Muir commented on LUCENE-5584:
-------------------------------------
{quote}
we don't actually need the byte arrays but we want to parse them into a value
object, hence reusing the output byte array is ok for us.
{quote}
If this is the case, then I am not sure you are using the correct
datastructure: it seems to me that a byte sequence output is not appropriate.
Since you do not care about the intermediate outputs, but have a "complicated"
intersection with the FST, why not use a numeric output, pointing to the result
data somewhere else?
> Allow FST read method to also recycle the output value when traversing FST
> --------------------------------------------------------------------------
>
> Key: LUCENE-5584
> URL: https://issues.apache.org/jira/browse/LUCENE-5584
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/FSTs
> Affects Versions: 4.7.1
> Reporter: Christian Ziech
>
> The FST class heavily reuses Arc instances when traversing the FST. The
> output of an Arc however is not reused. This can especially be important when
> traversing large portions of a FST and using the ByteSequenceOutputs and
> CharSequenceOutputs. Those classes create a new byte[] or char[] for every
> node read (which has an output).
> In our use case we intersect a lucene Automaton with a FST<BytesRef> much
> like it is done in
> org.apache.lucene.search.suggest.analyzing.FSTUtil.intersectPrefixPaths() and
> since the Automaton and the FST are both rather large tens or even hundreds
> of thousands of temporary byte array objects are created.
> One possible solution to the problem would be to change the
> org.apache.lucene.util.fst.Outputs class to have two additional methods (if
> you don't want to change the existing methods for compatibility):
> {code}
> /** Decode an output value previously written with {@link
> * #write(Object, DataOutput)} reusing the object passed in if possible */
> public abstract T read(DataInput in, T reuse) throws IOException;
> /** Decode an output value previously written with {@link
> * #writeFinalOutput(Object, DataOutput)}. By default this
> * just calls {@link #read(DataInput)}. This tries to reuse the object
> * passed in if possible */
> public T readFinalOutput(DataInput in, T reuse) throws IOException {
> return read(in, reuse);
> }
> {code}
> The new methods could then be used in the FST in the readNextRealArc() method
> passing in the output of the reused Arc. For most inputs they could even just
> invoke the original read(in) method.
> If you should decide to make that change I'd be happy to supply a patch
> and/or tests for the feature.
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