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

Nested Classes
Modifier and Type Class Description

protected class ConcurrentMergeScheduler.MergeThread

Field Summary

Fields
Modifier and Type	Field	Description
`protected static Comparator<ConcurrentMergeScheduler.MergeThread>`	`compareByMergeDocCount`
`protected Directory`	`dir`
`protected int`	`mergeThreadCount`
`protected List<ConcurrentMergeScheduler.MergeThread>`	`mergeThreads`
`protected IndexWriter`	`writer`

Constructor Summary

Constructors
Constructor Description

ConcurrentMergeScheduler()

Method Summary

All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods
Modifier and Type	Method	Description
`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

Class ConcurrentMergeScheduler

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

mergeThreads

dir

writer

mergeThreadCount

compareByMergeDocCount

Constructor Detail

ConcurrentMergeScheduler

Method Detail

setMaxThreadCount

getMaxThreadCount

setMaxMergeCount

getMaxMergeCount

getMergeThreadPriority

setMergeThreadPriority

updateMergeThreads

verbose

message

close

sync

mergeThreadCount

merge

doMerge

getMergeThread

handleMergeException

anyUnhandledExceptions

clearUnhandledExceptions

setTestMode