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https://issues.apache.org/jira/browse/LUCENE-8920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16974674#comment-16974674
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Michael Sokolov commented on LUCENE-8920:
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> In that case the version bump is not strictly needed since the new format is
> a superset of the old format, through I think we made the right choice of
> bumping the version in order to give a better error to users who would try to
> read 8.4 FSTs with an older release.
For example, this happened to us when trying to revert these changes, yet we
did not regenerate kuromoji and nori "dictionaries," which are FSTs.
> Reduce size of FSTs due to use of direct-addressing encoding
> -------------------------------------------------------------
>
> Key: LUCENE-8920
> URL: https://issues.apache.org/jira/browse/LUCENE-8920
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael Sokolov
> Priority: Minor
> Fix For: 8.4
>
> Attachments: TestTermsDictRamBytesUsed.java
>
> Time Spent: 4.5h
> Remaining Estimate: 0h
>
> Some data can lead to worst-case ~4x RAM usage due to this optimization.
> Several ideas were suggested to combat this on the mailing list:
> bq. I think we can improve thesituation here by tracking, per-FST instance,
> the size increase we're seeing while building (or perhaps do a preliminary
> pass before building) in order to decide whether to apply the encoding.
> bq. we could also make the encoding a bit more efficient. For instance I
> noticed that arc metadata is pretty large in some cases (in the 10-20 bytes)
> which make gaps very costly. Associating each label with a dense id and
> having an intermediate lookup, ie. lookup label -> id and then id->arc offset
> instead of doing label->arc directly could save a lot of space in some cases?
> Also it seems that we are repeating the label in the arc metadata when
> array-with-gaps is used, even though it shouldn't be necessary since the
> label is implicit from the address?
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