[jira] [Updated] (LUCENE-8084) FSTs can be very space-inefficient on array-expanded nodes

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[jira] [Updated] (LUCENE-8084) FSTs can be very space-inefficient on array-expanded nodes

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     [ https://issues.apache.org/jira/browse/LUCENE-8084?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Dawid Weiss updated LUCENE-8084:
    Attachment: capture-4.png

> FSTs can be very space-inefficient on array-expanded nodes
> ----------------------------------------------------------
>                 Key: LUCENE-8084
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8084
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Dawid Weiss
>            Priority: Minor
>         Attachments: capture-4.png
> We have FSTs which operate on a larger alphabet (keys in int) space and emit character sequence outputs. I noticed that certain nodes get expanded into fixed-size arrays to accelerate lookups (binary search). This has a potential problem, however, when the outputs emit larger blobs of data (say, one of the outputs is very long, all the others are small). Then the fixed-size array is very much overallocated, as evident on the attached picture.
> I wonder if it'd be better to encode the array as fixed-size, but without the outputs and use a local fixed-size pointer into a "value pool" somewhere next to the node's arcs. Theoretically this "value pool" could even be shared by all of automaton's nodes (saved once at the end or flushed periodically).
> Just a thought.

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