Mathias Henriksen created LUCENENET-640:
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Summary: Sequential IndexWriter performance in concurrent
environments.
Key: LUCENENET-640
URL: https://issues.apache.org/jira/browse/LUCENENET-640
Project: Lucene.Net
Issue Type: Bug
Components: Lucene.Net Core
Affects Versions: Lucene.Net 4.8.0
Reporter: Mathias Henriksen
Fix For: Lucene.Net 4.8.0
Attachments: AssertFinalBug.jpg, IdentityWeakReferenceBug.jpg,
Program.cs, overviewBug.jpg
When creating Lucene.Net indices in parallel, sequential-like performance is
experienced. Profiling 8 concurrent IndexWriter instances writing in parallel
shows that WeakIdentityMap::IdentityWeakReference::Equals spends most time
garbage collecting (94.91%) and TokenStream::AssertFinal (87.09% garbage
collecting) in my preliminary tests (see screenshots).
The
[WeakIdentityMap|https://github.com/apache/lucenenet/blob/master/src/Lucene.Net/Util/WeakIdentityMap.cs]
implementation uses an IdentityWeakReference as key, which is implemented as a
class. By inspection of this class, it is merely a
System.Runtime.InteropServices.GCHandle wrapper as can be seen in the mono
project, manually wrapping of this struct in a struct rather than a class -
will eliminate some of the immense amounts of garbage collection.
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