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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-5152) Lucene FST is not immutale
Date Thu, 01 Aug 2013 16:23:49 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-5152?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13726569#comment-13726569
] 

Robert Muir commented on LUCENE-5152:
-------------------------------------

I guess one question would be if its FSTs job to defend against bytesref bugs.

This issue was driven because there was a bytesref bug for suggester payloads.
The same kind of bug could happen, e.g. if someone uses DirectPostings and modifies the payload
coming back from the postings lists.

Should we clone payload bytes in the postings lists too? what about term dictionaries?

At some point then BytesRef is useless as a reference class because of a few bad apples trying
to use it as a ByteBuffer.
Ideally we would remove code that abuses BytesRef as a ByteBuffer instead. 

I don't mean to pick on your issue Simon, and it doesnt mean I object to the patch (though
I wonder about performance implications), I just see this as one of many in a larger issue.

                
> Lucene FST is not immutale
> --------------------------
>
>                 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
>
>
> 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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