org.apache.lucene.store

## Class NativeUnixDirectory

- java.lang.Object
- - org.apache.lucene.store.Directory
  - - org.apache.lucene.store.BaseDirectory
    - - org.apache.lucene.store.FSDirectory
      - - org.apache.lucene.store.NativeUnixDirectory

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public class NativeUnixDirectory
      extends FSDirectory

  A `Directory` implementation for all Unixes that uses DIRECT I/O to bypass OS level IO caching during merging. For all other cases (searching, writing) we delegate to the provided Directory instance.

  See Overview for more details.

  To use this you must compile NativePosixUtil.cpp (exposes Linux-specific APIs through JNI) for your platform, by running `ant build-native-unix`, and then putting the resulting `libNativePosixUtil.so` (from `lucene/build/native`) onto your dynamic linker search path.

  WARNING: this code is very new and quite easily could contain horrible bugs. For example, here's one known issue: if you use seek in `IndexOutput`, and then write more than one buffer's worth of bytes, then the file will be wrong. Lucene does not do this today (only writes small number of bytes after seek), but that may change.

  This directory passes Solr and Lucene tests on Linux and OS X; other Unixes should work but have not been tested! Use at your own risk.

  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `DEFAULT_MERGE_BUFFER_SIZE` Default buffer size before writing to disk (256 KB); larger means less IO load but more RAM and direct buffer storage space consumed during merging.
    `static long` | `DEFAULT_MIN_BYTES_DIRECT` Default min expected merge size before direct IO is used (10 MB):

    - ### Fields inherited from class org.apache.lucene.store.FSDirectory

      `directory`

    - ### Fields inherited from class org.apache.lucene.store.BaseDirectory

      `isOpen, lockFactory`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `NativeUnixDirectory(Path path, Directory delegate)` Create a new NIOFSDirectory for the named location with `FSLockFactory.getDefault()`.
    `NativeUnixDirectory(Path path, int mergeBufferSize, long minBytesDirect, LockFactory lockFactory, Directory delegate)` Create a new NIOFSDirectory for the named location.
    `NativeUnixDirectory(Path path, LockFactory lockFactory, Directory delegate)` Create a new NIOFSDirectory for the named location.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `IndexOutput` | `createOutput(String name, IOContext context)`
    `IndexInput` | `openInput(String name, IOContext context)`

    - ### Methods inherited from class org.apache.lucene.store.FSDirectory

      `close, createTempOutput, deleteFile, deletePendingFiles, ensureCanRead, fileLength, fsync, getDirectory, getPendingDeletions, listAll, listAll, open, open, rename, sync, syncMetaData, toString`

    - ### Methods inherited from class org.apache.lucene.store.BaseDirectory

      `ensureOpen, obtainLock`

    - ### Methods inherited from class org.apache.lucene.store.Directory

      `copyFrom, openChecksumInput`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Field Detail

    - #### DEFAULT_MERGE_BUFFER_SIZE

          public static final int DEFAULT_MERGE_BUFFER_SIZE

      Default buffer size before writing to disk (256 KB); larger means less IO load but more RAM and direct buffer storage space consumed during merging.
      See Also:
        Constant Field Values

    - #### DEFAULT_MIN_BYTES_DIRECT

          public static final long DEFAULT_MIN_BYTES_DIRECT

      Default min expected merge size before direct IO is used (10 MB):
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### NativeUnixDirectory

          public NativeUnixDirectory(Path path,
                                     int mergeBufferSize,
                                     long minBytesDirect,
                                     LockFactory lockFactory,
                                     Directory delegate)
                              throws IOException

      Create a new NIOFSDirectory for the named location.
      Parameters:
        `path` - the path of the directory
        `lockFactory` - to use
        `mergeBufferSize` - Size of buffer to use for merging. See `DEFAULT_MERGE_BUFFER_SIZE`.
        `minBytesDirect` - Merges, or files to be opened for reading, smaller than this will not use direct IO. See `DEFAULT_MIN_BYTES_DIRECT`
        `delegate` - fallback Directory for non-merges
      Throws:
        `IOException` - If there is a low-level I/O error

    - #### NativeUnixDirectory

          public NativeUnixDirectory(Path path,
                                     LockFactory lockFactory,
                                     Directory delegate)
                              throws IOException

      Create a new NIOFSDirectory for the named location.
      Parameters:
        `path` - the path of the directory
        `lockFactory` - the lock factory to use
        `delegate` - fallback Directory for non-merges
      Throws:
        `IOException` - If there is a low-level I/O error

    - #### NativeUnixDirectory

          public NativeUnixDirectory(Path path,
                                     Directory delegate)
                              throws IOException

      Create a new NIOFSDirectory for the named location with `FSLockFactory.getDefault()`.
      Parameters:
        `path` - the path of the directory
        `delegate` - fallback Directory for non-merges
      Throws:
        `IOException` - If there is a low-level I/O error

  - ### Method Detail

    - #### openInput

          public IndexInput openInput(String name,
                                      IOContext context)
                               throws IOException

      Specified by:
        `openInput` in class `Directory`
      Throws:
        `IOException`

    - #### createOutput

          public IndexOutput createOutput(String name,
                                          IOContext context)
                                   throws IOException

      Overrides:
        `createOutput` in class `FSDirectory`
      Throws:
        `IOException`

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