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Posted to issues@lucene.apache.org by "Adrien Grand (Jira)" <ji...@apache.org> on 2019/11/01 14:12:00 UTC
[jira] [Commented] (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:comment-tabpanel&focusedCommentId=16964854#comment-16964854 ]
Adrien Grand commented on LUCENE-8920:
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Maybe we should update the naming with your proposed approach, e.g. "indexed" or something along those lines instead of "direct addressing" which suggests nodes are directly addressed by their label like in Mike's previous patch?
Out of curiosity have you looked into no longer explicitly serializing labels with this new approach since labels can be inferred from the bitset?
> 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
> Attachments: TestTermsDictRamBytesUsed.java
>
> Time Spent: 3h 20m
> 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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