[
https://issues.apache.org/jira/browse/LUCENE-8962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17028113#comment-17028113
]
David Smiley commented on LUCENE-8962:
--------------------------------------
Indeed, I meant "small bus factor" :) I'm looking deeper at Michael Froh's PR
this weekend, and by necessity the pertinent parts of IndexWriter.
> Well, using {{SerialMergeScheduler}} allows the test to pass, since the
>merges kicked off due to new segments after the commit will run, synchronously
>(using the main thread in your test) to completion.
Yes, it's not "realistic", but my objective in this code snippet was merely to
demonstrate that the _combination_ of a merge policy and a merge scheduler have
the ability to affect the searchable segments on commit when using the NRT
Reader/Searcher. Apparently it doesn't work if a normal (non-NRT
Reader/Searcher) is opened; I can see that. Maybe this is a shortcoming of
IndexWriter; why shouldn't IW be consistent on this matter?
It's not apparent to me that we need a new method on the MergePolicy when the
MergeTrigger parameter is able to differentiate the types of merges so that a
MP is able to behave differently depending on the circumstance. Am I unclear
on 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
> Attachments: LUCENE-8962_demo.png
>
> Time Spent: 4h 40m
> 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!
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
