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https://issues.apache.org/jira/browse/LUCENE-5152?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13733454#comment-13733454
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Michael McCandless commented on LUCENE-5152:
--------------------------------------------
bq. can you elaborate what you are concerned about?
I'm worried about the O(N^2) cost of the assert: for every arc (single
byte of each term in a seekExact) we are iterating over all root arcs
(up to 256 arcs) in this assert.
bq. findTargetArc is the only place where we actually use this cache?
Ahh that's true, I hadn't realized that.
Maybe, instead, we can move the assert just inside the if that
actually uses the cached arcs? Ie, put it here:
{code}
if (follow.target == startNode && labelToMatch < cachedRootArcs.length) {
assert assertRootArcs();
...
}
{code}
This would address my concern: the cost becomes O(N) not O(N^2). And
the coverage is the same?
> 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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