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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-994) Change defaults in IndexWriter to maximize "out of the box" performance
Date Thu, 25 Oct 2007 18:32:50 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12537691
] 

Michael McCandless commented on LUCENE-994:
-------------------------------------------

When you close the writer & open a reader, the reader should see all
docs added, regardless of whether the writer was using concurrent
merge scheduler or serial merge scheduler, autoCommit true or false,
flushing by ram or by doc count, etc.

IndexWriter.close() first flushes any buffered docs to a new segment,
and then allows merges to run if they are necessary.  It will also
wait for all merges to finish (in the case of concurrent merge
scheduler) unless you call close(false) which will abort all running
merges.

If you're not seeing this behavior then something is seriously wrong!
Can you post some more details about how you see this intermittant
failure?


> Change defaults in IndexWriter to maximize "out of the box" performance
> -----------------------------------------------------------------------
>
>                 Key: LUCENE-994
>                 URL: https://issues.apache.org/jira/browse/LUCENE-994
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.3
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.3
>
>         Attachments: LUCENE-994.patch, writerinfo.zip
>
>
> This is follow-through from LUCENE-845, LUCENE-847 and LUCENE-870;
> I'll commit this once those three are committed.
> Out of the box performance of IndexWriter is maximized when flushing
> by RAM instead of a fixed document count (the default today) because
> documents can vary greatly in size.
> Likewise, merging performance should be faster when merging by net
> segment size since, to minimize the net IO cost of merging segments
> over time, you want to merge segments of equal byte size.
> Finally, ConcurrentMergeScheduler improves indexing speed
> substantially (25% in a simple initial test in LUCENE-870) because it
> runs the merges in the backround and doesn't block
> add/update/deleteDocument calls.  Most machines have concurrency
> between CPU and IO and so it makes sense to default to this
> MergeScheduler.
> Note that these changes will break users of ParallelReader because the
> parallel indices will no longer have matching docIDs.  Such users need
> to switch IndexWriter back to flushing by doc count, and switch the
> MergePolicy back to LogDocMergePolicy.  It's likely also necessary to
> switch the MergeScheduler back to SerialMergeScheduler to ensure
> deterministic docID assignment.
> I think the combination of these three default changes, plus other
> performance improvements for indexing (LUCENE-966, LUCENE-843,
> LUCENE-963, LUCENE-969, LUCENE-871, etc.) should make for some sizable
> performance gains Lucene 2.3!

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