## org.apache.lucene.index
Class ConcurrentMergeScheduler

    java.lang.Object
      org.apache.lucene.index.MergeScheduler
          org.apache.lucene.index.ConcurrentMergeScheduler

    public class ConcurrentMergeScheduler

extends MergeScheduler

A `MergeScheduler` that runs each merge using a separate thread.

Specify the max number of threads that may run at once with `setMaxThreadCount(int)`.

Separately specify the maximum number of simultaneous merges with `setMaxMergeCount(int)`. If the number of merges exceeds the max number of threads then the largest merges are paused until one of the smaller merges completes.

If more than `getMaxMergeCount()` merges are requested then this class will forcefully throttle the incoming threads by pausing until one more more merges complete.

Nested Class Summary
`protected class` `ConcurrentMergeScheduler.MergeThread`

Field Summary
`protected static Comparator<ConcurrentMergeScheduler.MergeThread>` `compareByMergeDocCount`
`protected Directory` `dir`
`protected int` `mergeThreadCount`
`protected List<ConcurrentMergeScheduler.MergeThread>` `mergeThreads`
`protected IndexWriter` `writer`

Constructor Summary
`ConcurrentMergeScheduler()`

Method Summary
`static boolean` `anyUnhandledExceptions()` Used for testing
`static void` `clearUnhandledExceptions()`
`void` `close()` Close this MergeScheduler.
`protected void` `doMerge(MergePolicy.OneMerge merge)` Does the actual merge, by calling `IndexWriter.merge(org.apache.lucene.index.MergePolicy.OneMerge)`
`int` `getMaxMergeCount()` See `setMaxMergeCount(int)`.
`int` `getMaxThreadCount()`
`protected ConcurrentMergeScheduler.MergeThread` `getMergeThread(IndexWriter writer, MergePolicy.OneMerge merge)` Create and return a new MergeThread
`int` `getMergeThreadPriority()` Return the priority that merge threads run at.
`protected void` `handleMergeException(Throwable exc)` Called when an exception is hit in a background merge thread
`void` `merge(IndexWriter writer)` Run the merges provided by `IndexWriter.getNextMerge()`.
`protected int` `mergeThreadCount()` Returns the number of merge threads that are alive.
`protected void` `message(String message)` Outputs the given message - this method assumes `verbose()` was called and returned true.
`void` `setMaxMergeCount(int count)` Sets the max # simultaneous merges that are allowed.
`void` `setMaxThreadCount(int count)` Sets the max # simultaneous merge threads that should be running at once.
`void` `setMergeThreadPriority(int pri)` Set the base priority that merge threads run at.
`static void` `setTestMode()` Deprecated. this test mode code will be removed in a future release
`void` `sync()` Wait for any running merge threads to finish
`protected void` `updateMergeThreads()` Called whenever the running merges have changed, to pause & unpause threads.
`protected boolean` `verbose()` Returns true if verbosing is enabled.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### mergeThreads

    protected List<ConcurrentMergeScheduler.MergeThread> mergeThreads

### dir

    protected Directory dir

### writer

    protected IndexWriter writer

### mergeThreadCount

    protected int mergeThreadCount

### compareByMergeDocCount

    protected static final Comparator<ConcurrentMergeScheduler.MergeThread> compareByMergeDocCount

Constructor Detail

### ConcurrentMergeScheduler

    public ConcurrentMergeScheduler()

Method Detail

### setMaxThreadCount

    public void setMaxThreadCount(int count)

  Sets the max # simultaneous merge threads that should be running at once. This must be <= `setMaxMergeCount(int)`.

### getMaxThreadCount

    public int getMaxThreadCount()

  See Also:
    `setMaxThreadCount(int)`

### setMaxMergeCount

    public void setMaxMergeCount(int count)

  Sets the max # simultaneous merges that are allowed. If a merge is necessary yet we already have this many threads running, the incoming thread (that is calling add/updateDocument) will block until a merge thread has completed. Note that we will only run the smallest `setMaxThreadCount(int)` merges at a time.

### getMaxMergeCount

    public int getMaxMergeCount()

  See `setMaxMergeCount(int)`.

### getMergeThreadPriority

    public int getMergeThreadPriority()

  Return the priority that merge threads run at. By default the priority is 1 plus the priority of (ie, slightly higher priority than) the first thread that calls merge.

### setMergeThreadPriority

    public void setMergeThreadPriority(int pri)

  Set the base priority that merge threads run at. Note that CMS may increase priority of some merge threads beyond this base priority. It's best not to set this any higher than Thread.MAX_PRIORITY-maxThreadCount, so that CMS has room to set relative priority among threads.

### updateMergeThreads

    protected void updateMergeThreads()

  Called whenever the running merges have changed, to pause & unpause threads. This method sorts the merge threads by their merge size in descending order and then pauses/unpauses threads from first to last -- that way, smaller merges are guaranteed to run before larger ones.

### verbose

    protected boolean verbose()

  Returns true if verbosing is enabled. This method is usually used in conjunction with `message(String)`, like that:

       if (verbose()) {
         message("your message");
       }

### message

    protected void message(String message)

  Outputs the given message - this method assumes `verbose()` was called and returned true.

### close

    public void close()

  Description copied from class: `MergeScheduler`
  Close this MergeScheduler.

  Specified by:
    `close` in class `MergeScheduler`

### sync

    public void sync()

  Wait for any running merge threads to finish

### mergeThreadCount

    protected int mergeThreadCount()

  Returns the number of merge threads that are alive. Note that this number is ≤ `mergeThreads` size.

### merge

    public void merge(IndexWriter writer)
               throws IOException

  Description copied from class: `MergeScheduler`
  Run the merges provided by `IndexWriter.getNextMerge()`.

  Specified by:
    `merge` in class `MergeScheduler`
  Throws:
    `IOException`

### doMerge

    protected void doMerge(MergePolicy.OneMerge merge)
                    throws IOException

  Does the actual merge, by calling `IndexWriter.merge(org.apache.lucene.index.MergePolicy.OneMerge)`

  Throws:
    `IOException`

### getMergeThread

    protected ConcurrentMergeScheduler.MergeThread getMergeThread(IndexWriter writer,
                                                                  MergePolicy.OneMerge merge)
                                                           throws IOException

  Create and return a new MergeThread

  Throws:
    `IOException`

### handleMergeException

    protected void handleMergeException(Throwable exc)

  Called when an exception is hit in a background merge thread

### anyUnhandledExceptions

    public static boolean anyUnhandledExceptions()

  Used for testing

### clearUnhandledExceptions

    public static void clearUnhandledExceptions()

### setTestMode

    @Deprecated
    public static void setTestMode()

  Deprecated. this test mode code will be removed in a future release