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https://issues.apache.org/jira/browse/LUCENE-5912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14115043#comment-14115043
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Michael McCandless commented on LUCENE-5912:
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Sheesh, so it is actually sharing SegmentReaders from the writer's pool? Talk
about confusing code ... none of can figure out how it works.
Maybe we should add a simple test case confirming that readers are in fact in
common, to be sure :) I'll work on this.
> Non-NRT directory readers don't reuse segments maintained IndexWriter's
> segment reader pool
> -------------------------------------------------------------------------------------------
>
> Key: LUCENE-5912
> URL: https://issues.apache.org/jira/browse/LUCENE-5912
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Affects Versions: 4.6.1
> Reporter: Vitaly Funstein
>
> Currently, if you attempt to open a reader into an index at a specific commit
> point, it will always behave as though it's opening a completely new index -
> even if one were to use the {{DirectoryReader.openIfChanged(DirectoryReader,
> IndexCommit)}} API, and pass in an NRT reader instance. What should ideally
> happen here is that the SegmentReader pool managed by IndexWriter linked to
> the NRT reader gets reused for the commit point open as much as possible, to
> avoid wasting heap space.
> The problem becomes evident when looking at the code in DirectoryReader:
> {code}
> protected DirectoryReader doOpenIfChanged(final IndexCommit commit) throws
> IOException {
> ensureOpen();
> // If we were obtained by writer.getReader(), re-ask the
> // writer to get a new reader.
> if (writer != null) {
> return doOpenFromWriter(commit);
> } else {
> return doOpenNoWriter(commit);
> }
> }
> private DirectoryReader doOpenFromWriter(IndexCommit commit) throws
> IOException {
> if (commit != null) {
> return doOpenFromCommit(commit);
> }
> ......
> {code}
> Looks like the fact that a commit point is being re-opened trumps the
> presence of the associated IndexWriter.
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