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Posted to issues@lucene.apache.org by "Adrien Grand (Jira)" <ji...@apache.org> on 2019/11/14 08:44:00 UTC
[jira] [Resolved] (LUCENE-8920) Reduce size of FSTs due to use of
direct-addressing encoding
[ https://issues.apache.org/jira/browse/LUCENE-8920?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Adrien Grand resolved LUCENE-8920.
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Fix Version/s: 8.4
Resolution: Fixed
There were a few conflicts when backporting to branch_8x, so you might want to take a second look [~sokolov] [~bruno.roustant] to make sure I did not get anything wrong.
> 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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