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https://issues.apache.org/jira/browse/LUCENE-8962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17053380#comment-17053380
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ASF subversion and git services commented on LUCENE-8962:
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Commit 90aced5a51f92ffd6e97449eb7c44aacc643c8a3 in lucene-solr's branch
refs/heads/branch_8x from Michael Sokolov
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=90aced5 ]
LUCENE-8962: Split test case (#1313)
* LUCENE-8962: Simplify test case
The testMergeOnCommit test case was trying to verify too many things
at once: basic semantics of merge on commit and proper behavior when
a bunch of indexing threads are writing and committing all at once.
Now we just verify basic behavior, with strict assertions on invariants, while
leaving it to MockRandomMergePolicy to enable merge on commit in existing
test cases to verify that indexing generally works as expected and no new
unexpected exceptions are thrown.
* LUCENE-8962: Only update toCommit if merge was committed
The code was previously assuming that if mergeFinished() was called and
isAborted() was false, then the merge must have completed successfully.
Instead, we should know for sure if a given merge was committed, and
only then update our pending commit SegmentInfos.
> 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: 8.5
>
> Attachments: LUCENE-8962_demo.png
>
> Time Spent: 9h 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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