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Posted to issues@lucene.apache.org by "Robert Muir (Jira)" <ji...@apache.org> on 2020/03/06 10:47:00 UTC
[jira] [Resolved] (LUCENE-9264) Remove SimpleFSDirectory in favor
of NIOFsDirectory
[ https://issues.apache.org/jira/browse/LUCENE-9264?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Robert Muir resolved LUCENE-9264.
---------------------------------
Resolution: Fixed
> Remove SimpleFSDirectory in favor of NIOFsDirectory
> ---------------------------------------------------
>
> Key: LUCENE-9264
> URL: https://issues.apache.org/jira/browse/LUCENE-9264
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Yannick Welsch
> Priority: Minor
> Fix For: master (9.0)
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> {{SimpleFSDirectory}} looks to duplicate what's already offered by {{NIOFsDirectory}}. The only difference is that {{SimpleFSDirectory}} is using non-positional reads on the {{FileChannel}} (i.e., reads that are stateful, changing the current position), and {{SimpleFSDirectory}} therefore has to externally synchronize access to the read method.
> On Windows, positional reads are not supported, which is why {{FileChannel}} is already internally using synchronization to guarantee only access by one thread at a time for positional reads (see {{read(ByteBuffer dst, long position)}} in {{FileChannelImpl}}, and {{FileDispatcher.needsPositionLock}}, which returns true on Windows) and the JDK implementation for Windows is emulating positional reads by using non-positional ones, see [http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/windows/native/sun/nio/ch/FileDispatcherImpl.c#l139].
> This means that on Windows, there should be no difference between {{NIOFsDirectory}} and {{SimpleFSDirectory}} in terms of performance (it should be equally poor as both implementations only allow one thread at a time to read). On Linux/Mac, {{NIOFsDirectory}} is superior to {{SimpleFSDirectory}}, however, as positional reads (pread) can be done concurrently.
> My proposal is to remove {{SimpleFSDirectory}} and replace its uses with {{NIOFsDirectory}}, given how similar these two directory implementations are ({{SimpleFSDirectory}} isn't really simpler).
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