[jira] [Commented] (LUCENE-5152) Lucene FST is not immutable

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[jira] [Commented] (LUCENE-5152) Lucene FST is not immutable

Markus Jelsma (Jira)

    [ https://issues.apache.org/jira/browse/LUCENE-5152?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13727986#comment-13727986 ]

Michael McCandless commented on LUCENE-5152:
--------------------------------------------

I know we make no claims about performance when assertions are enabled...

But it seems like this commit could substantially slow things down, since we call assertRootArcs, which is O(N) where N = number of root arcs, for every call to findTargetArc = likely called in hotspots.

Maybe, we could move the call to e.g. FST.getBytesReader?
               

> Lucene FST is not immutable
> ---------------------------
>
>                 Key: LUCENE-5152
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5152
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/FSTs
>    Affects Versions: 4.4
>            Reporter: Simon Willnauer
>            Priority: Blocker
>             Fix For: 5.0, 4.5
>
>         Attachments: LUCENE-5152.patch, LUCENE-5152.patch, LUCENE-5152.patch
>
>
> a spinnoff from LUCENE-5120 where the analyzing suggester modified a returned output from and FST (BytesRef) which caused sideffects in later execution.
> I added an assertion into the FST that checks if a cached root arc is modified and in-fact this happens for instance in our MemoryPostingsFormat and I bet we find more places. We need to think about how to make this less trappy since it can cause bugs that are super hard to find.

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