shbhar commented on code in PR #16923:
URL: https://github.com/apache/lucene/pull/16923#discussion_r4463548548
##########
lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java:
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@@ -463,10 +463,12 @@ private DirectoryReader doOpenFromWriter(IndexCommit
commit, ExecutorService exe
return null;
}
- DirectoryReader reader = writer.getReader(applyAllDeletes,
writeAllDeletes);
+ StandardDirectoryReader reader = writer.getReader(applyAllDeletes,
writeAllDeletes);
- // If in fact no changes took place, return null:
- if (reader.getVersion() == segmentInfos.getVersion()) {
+ // If in fact no changes took place, return null. A commit that was
syncing files when this
+ // reader was opened changes the referenced segments_N once it completes,
but not the version:
+ if (reader.getVersion() == segmentInfos.getVersion()
+ && reader.segmentInfos.getLastGeneration() ==
segmentInfos.getLastGeneration()) {
Review Comment:
There might be one more edge case. For this "lets bump the version if
reader is opened during writer commit solution" now w1 writer can have in
memory version of 8 and on disk of 7, the 8 version can be picked up by a new
r1 reader (which is then cached by the version). Then w1 is closed with no
other changes but 8 is never made durable. Another writer w2 opens and gets
version 7, makes a change which makes the version 8 again and a new reader r2
on it then gets version 8 same as r1 (so we land in the same problem)? I think
this will also be unexpected especially in this case where there was no crash
or rollback etc. (for rollback this cross-writer same version situation might
be expected)
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