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improve IW javadocs

This commit is contained in:
Mike McCandless 2016-12-02 15:30:37 -05:00
parent fcccd317dd
commit 58476b1675
1 changed files with 18 additions and 13 deletions
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31
lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
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@ -133,19 +133,24 @@ import org.apache.lucene.util.Version;
<a name="deletionPolicy"></a>
<p>Expert: <code>IndexWriter</code> allows an optional
{@link IndexDeletionPolicy} implementation to be
specified. You can use this to control when prior commits
are deleted from the index. The default policy is {@link
KeepOnlyLastCommitDeletionPolicy} which removes all prior
commits as soon as a new commit is done (this matches
behavior before 2.2). Creating your own policy can allow
you to explicitly keep previous "point in time" commits
alive in the index for some time, to allow readers to
refresh to the new commit without having the old commit
deleted out from under them. This is necessary on
filesystems like NFS that do not support "delete on last
close" semantics, which Lucene's "point in time" search
normally relies on. </p>
{@link IndexDeletionPolicy} implementation to be specified. You
can use this to control when prior commits are deleted from
the index. The default policy is {@link KeepOnlyLastCommitDeletionPolicy}
which removes all prior commits as soon as a new commit is
done. Creating your own policy can allow you to explicitly
keep previous "point in time" commits alive in the index for
some time, either because this is useful for your application,
or to give readers enough time to refresh to the new commit
without having the old commit deleted out from under them.
The latter is necessary when multiple computers take turns opening
their own {@code IndexWriter} and {@code IndexReader}s
against a single shared index mounted via remote filesystems
like NFS which do not support "delete on last close" semantics.
A single computer accessing an index via NFS is fine with the
default deletion policy since NFS clients emulate "delete on
last close" locally. That said, accessing an index via NFS
will likely result in poor performance compared to a local IO
device. </p>
<a name="mergePolicy"></a> <p>Expert:
<code>IndexWriter</code> allows you to separately change