[
https://issues.apache.org/jira/browse/LUCENE-8962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17145871#comment-17145871
]
Michael McCandless commented on LUCENE-8962:
--------------------------------------------
Ooh, found another failing test (after 341 full iterations), and this one does
reproduce!
{noformat}
[junit4:pickseed] Seed property 'tests.seed' already defined: D75F6483D2E6C62C
[junit4] <JUnit4> says ¡Hola! Master seed: D75F6483D2E6C62C
[junit4] Executing 1 suite with 1 JVM.
[junit4]
[junit4] Started J0 PID(3328881@localhost).
[junit4] Suite: org.apache.lucene.index.TestIndexWriterMergePolicy
[junit4] 2> NOTE: reproduce with: ant test
-Dtestcase=TestIndexWriterMergePolicy -Dtests.method=testMergeOnCommit
-Dtests.seed=D75F6483D2E6C62C -Dtests.slow=true -Dtests.badapples=tr\
ue -Dtests.locale=en-CM -Dtests.timezone=Eire -Dtests.asserts=true
-Dtests.file.encoding=UTF-8
[junit4] FAILURE 0.27s | TestIndexWriterMergePolicy.testMergeOnCommit <<<
[junit4] > Throwable #1: java.lang.AssertionError: expected:<1> but
was:<6>
[junit4] > at
__randomizedtesting.SeedInfo.seed([D75F6483D2E6C62C:F3D97E843303240C]:0)
[junit4] > at
org.apache.lucene.index.TestIndexWriterMergePolicy.testMergeOnCommit(TestIndexWriterMergePolicy.java:340)
[junit4] > at
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[junit4] > at
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[junit4] > at
java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[junit4] > at
java.base/java.lang.reflect.Method.invoke(Method.java:566)
[junit4] > at java.base/java.lang.Thread.run(Thread.java:834)
[junit4] 2> Jun 25, 2020 5:41:39 PM
com.carrotsearch.randomizedtesting.ThreadLeakControl checkThreadLeaks
[junit4] 2> WARNING: Will linger awaiting termination of 1 leaked
thread(s).
[junit4] 2> NOTE: test params are: codec=CheapBastard,
sim=Asserting(RandomSimilarity(queryNorm=true): {content=DFI(ChiSquared)}),
locale=en-CM, timezone=Eire
[junit4] 2> NOTE: Linux 5.5.6-arch1-1 amd64/Oracle Corporation 11.0.6
(64-bit)/cpus=128,threads=1,free=477412792,total=536870912
[junit4] 2> NOTE: All tests run in this JVM: [TestIndexWriterMergePolicy]
[junit4] Completed [1/1 (1!)] in 0.56s, 1 test, 1 failure <<< FAILURES!
[junit4]
[junit4]
[junit4] Tests with failures [seed: D75F6483D2E6C62C]:
[junit4] -
org.apache.lucene.index.TestIndexWriterMergePolicy.testMergeOnCommit
[junit4]
[junit4]
[junit4] JVM J0: 0.34 .. 1.45 = 1.11s
[junit4] Execution time total: 1.45 sec.
[junit4] Tests summary: 1 suite, 1 test, 1 failure {noformat}
> 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, test.diff
>
> Time Spent: 20h 20m
> 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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