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https://issues.apache.org/jira/browse/LUCENE-10059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17404552#comment-17404552
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Tomoko Uchida commented on LUCENE-10059:
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I'm sorry, I'm not familiar with the particular reason why KoreanTokenizer had
to be forked from JapaneseTokenizer when it was created. I think that might
have been explained or discussed in the original KoreanTokenizer issue but
can't find it soon.
> Assertion error in JapaneseTokenizer backtrace
> ----------------------------------------------
>
> Key: LUCENE-10059
> URL: https://issues.apache.org/jira/browse/LUCENE-10059
> Project: Lucene - Core
> Issue Type: Bug
> Affects Versions: 8.8
> Reporter: Anh Dung Bui
> Priority: Major
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> There is a rare case which causes an AssertionError in the backtrace step of
> JapaneseTokenizer that we (Amazon Product Search) found in our tests.
> If there is a text span of length 1024 (determined by
> [MAX_BACKTRACE_GAP|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L116])
> where the regular backtrace is not called, a [forced
> backtrace|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L781]
> will be applied. If the partially best path at this point happens to end at
> the last pos, and since there is always a [final
> backtrace|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L1044]
> applied at the end, the final backtrace will try to backtrace from and to
> the same position, causing an AssertionError in RollingCharBuffer.get() when
> it tries to generate an empty buffer.
> We are fixing it by returning prematurely in the backtrace() method when the
> from and to pos are the same:
> {code:java}
> if (endPos == lastBackTracePos) {
> return;
> }
> {code}
> The backtrace() method is essentially no-op when this condition happens, thus
> when _-ea_ is not enabled, it can still output the correct tokens.
> We will open a PR for this issue.
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