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https://issues.apache.org/jira/browse/LUCENE-8962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17142197#comment-17142197
]
Simon Willnauer commented on LUCENE-8962:
-----------------------------------------
I attached a log file with a failure and index writer logging enabled. I think
I have a smoking gun here:
{noformat}
[junit4] 1> IW 2 [2020-06-22T15:33:08.479370Z; Lucene Merge Thread #31]:
merged segment _2f(9.0.0):c1:[diagnostics={os.version=10.14.6,
mergeMaxNumSegments=-1, java.version=12.0.1, java.vm.version=12.0.1+12,
lucene.version=9.0.0, timestamp=1592839988473, os=Mac OS X,
java.runtime.version=12.0.1+12, mergeFactor=1, os.arch=x86_64, source=merge,
java.vendor=Oracle
Corporation}]:[attributes={Lucene50StoredFieldsFormat.mode=BEST_SPEED}]
:id=70ut1o7n9kgx798rria9sma3n is 100% deleted; skipping insert
[junit4] 1> SM 2 [2020-06-22T15:33:08.479615Z; Lucene Merge Thread #32]: 0
msec to write field infos [29 docs]
[junit4] 1> IFD 2 [2020-06-22T15:33:08.479662Z; Lucene Merge Thread #31]:
will delete new file "_2f.cfe"
[junit4] 1> IFD 2 [2020-06-22T15:33:08.479712Z; Lucene Merge Thread #31]:
will delete new file "_2f.cfs"
[junit4] 1> IFD 2 [2020-06-22T15:33:08.479740Z; Lucene Merge Thread #31]:
will delete new file "_2f.si"
[junit4] 1> IFD 2 [2020-06-22T15:33:08.479770Z; Lucene Merge Thread #31]:
delete [_2f.cfe, _2f.cfs, _2f.si]
{noformat}
and further down
{noformat}
[junit4] 2> Caused by: java.nio.file.NoSuchFileException: _2f.cfs
[junit4] 2> at
org.apache.lucene.store.ByteBuffersDirectory.deleteFile(ByteBuffersDirectory.java:148)
[junit4] 2> at
org.apache.lucene.store.MockDirectoryWrapper.deleteFile(MockDirectoryWrapper.java:607)
[junit4] 2> at
org.apache.lucene.store.LockValidatingDirectoryWrapper.deleteFile(LockValidatingDirectoryWrapper.java:38)
[junit4] 2> at
org.apache.lucene.index.IndexFileDeleter.deleteFile(IndexFileDeleter.java:696)
[junit4] 2> at
org.apache.lucene.index.IndexFileDeleter.deleteFiles(IndexFileDeleter.java:690)
[junit4] 2> at
org.apache.lucene.index.IndexFileDeleter.decRef(IndexFileDeleter.java:589)
[junit4] 2> at
org.apache.lucene.index.IndexFileDeleter.deleteCommits(IndexFileDeleter.java:382)
[junit4] 2> at
org.apache.lucene.index.IndexFileDeleter.checkpoint(IndexFileDeleter.java:527)
[junit4] 2> at
org.apache.lucene.index.IndexWriter.finishCommit(IndexWriter.java:3546)
[junit4] 2> at
org.apache.lucene.index.IndexWriter.commitInternal(IndexWriter.java:3502)
[junit4] 2> at
org.apache.lucene.index.IndexWriter.commit(IndexWriter.java:3452)
[junit4] 2> at
org.apache.lucene.index.TestIndexWriter.lambda$testRandomOperations$48(TestIndexWriter.java:3879)
[junit4] 2> ... 1 more
[junit4] 2>
{noformat}
I think we are not respecting the fact that it's fully deleted and dropped
because of this before we get a chance to incRef the segment. I will work on a
patch for this.
> Can we merge small segments during refresh, for faster searching?
> -----------------------------------------------------------------
>
> Key: LUCENE-8962
> URL: https://issues.apache.org/jira/browse/LUCENE-8962
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Reporter: Michael McCandless
> Priority: Major
> Fix For: 8.6
>
> Attachments: LUCENE-8962_demo.png, failed-tests.patch, failure_log.txt
>
> Time Spent: 18h 50m
> Remaining Estimate: 0h
>
> With near-real-time search we ask {{IndexWriter}} to write all in-memory
> segments to disk and open an {{IndexReader}} to search them, and this is
> typically a quick operation.
> However, when you use many threads for concurrent indexing, {{IndexWriter}}
> will accumulate write many small segments during {{refresh}} and this then
> adds search-time cost as searching must visit all of these tiny segments.
> The merge policy would normally quickly coalesce these small segments if
> given a little time ... so, could we somehow improve {{IndexWriter'}}s
> refresh to optionally kick off merge policy to merge segments below some
> threshold before opening the near-real-time reader? It'd be a bit tricky
> because while we are waiting for merges, indexing may continue, and new
> segments may be flushed, but those new segments shouldn't be included in the
> point-in-time segments returned by refresh ...
> One could almost do this on top of Lucene today, with a custom merge policy,
> and some hackity logic to have the merge policy target small segments just
> written by refresh, but it's tricky to then open a near-real-time reader,
> excluding newly flushed but including newly merged segments since the refresh
> originally finished ...
> I'm not yet sure how best to solve this, so I wanted to open an issue for
> discussion!
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