HeapMemStoreLAB (Apache HBase 1.2.12 API)

java.lang.Object
- org.apache.hadoop.hbase.regionserver.HeapMemStoreLAB

All Implemented Interfaces:

MemStoreLAB
```
@InterfaceAudience.Private
public class HeapMemStoreLAB
extends Object
implements MemStoreLAB
```
A memstore-local allocation buffer.
The MemStoreLAB is basically a bump-the-pointer allocator that allocates big (2MB) byte[] chunks from and then doles it out to threads that request slices into the array.
The purpose of this class is to combat heap fragmentation in the regionserver. By ensuring that all KeyValues in a given memstore refer only to large chunks of contiguous memory, we ensure that large blocks get freed up when the memstore is flushed.
Without the MSLAB, the byte array allocated during insertion end up interleaved throughout the heap, and the old generation gets progressively more fragmented until a stop-the-world compacting collection occurs.
TODO: we should probably benchmark whether word-aligning the allocations would provide a performance improvement - probably would speed up the Bytes.toLong/Bytes.toInt calls in KeyValue, but some of those are cached anyway

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

(package private) static class HeapMemStoreLAB.Chunk
A chunk of memory out of which allocations are sliced.

Nested Classes
Modifier and Type	Class and Description
`(package private) static class`	`HeapMemStoreLAB.Chunk` A chunk of memory out of which allocations are sliced.

Field Summary

Fields
Modifier and Type	Field and Description
`(package private) static int`	`CHUNK_SIZE_DEFAULT`
`(package private) static String`	`CHUNK_SIZE_KEY`
`private MemStoreChunkPool`	`chunkPool`
`private BlockingQueue<HeapMemStoreLAB.Chunk>`	`chunkQueue`
`(package private) int`	`chunkSize`
`private boolean`	`closed`
`private AtomicReference<HeapMemStoreLAB.Chunk>`	`curChunk`
`(package private) static org.apache.commons.logging.Log`	`LOG`
`(package private) static int`	`MAX_ALLOC_DEFAULT`
`(package private) static String`	`MAX_ALLOC_KEY`
`(package private) int`	`maxAlloc`
`private AtomicInteger`	`openScannerCount`
`private AtomicBoolean`	`reclaimed`

Constructor Summary

Constructors
Constructor and Description

HeapMemStoreLAB()

HeapMemStoreLAB(org.apache.hadoop.conf.Configuration conf)

Constructors
Constructor and Description
`HeapMemStoreLAB()`
`HeapMemStoreLAB(org.apache.hadoop.conf.Configuration conf)`

Method Summary

Methods
Modifier and Type	Method and Description
`ByteRange`	`allocateBytes(int size)` Allocate a slice of the given length.
`void`	`close()` Close this instance since it won't be used any more, try to put the chunks back to pool
`void`	`decScannerCount()` Called when closing a scanner on the data of this MemStoreLAB
`(package private) BlockingQueue<HeapMemStoreLAB.Chunk>`	`getChunkQueue()`
`(package private) HeapMemStoreLAB.Chunk`	`getCurrentChunk()`
`private HeapMemStoreLAB.Chunk`	`getOrMakeChunk()` Get the current chunk, or, if there is no current chunk, allocate a new one from the JVM.
`void`	`incScannerCount()` Called when opening a scanner on the data of this MemStoreLAB
`private void`	`tryRetireChunk(HeapMemStoreLAB.Chunk c)` Try to retire the current chunk if it is still `c`.

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

- Field Detail
  - CHUNK_SIZE_KEY
```
static final String CHUNK_SIZE_KEY
```
    See Also:
    Constant Field Values
  - CHUNK_SIZE_DEFAULT
```
static final int CHUNK_SIZE_DEFAULT
```
    See Also:
    Constant Field Values
  - MAX_ALLOC_KEY
```
static final String MAX_ALLOC_KEY
```
    See Also:
    Constant Field Values
  - MAX_ALLOC_DEFAULT
```
static final int MAX_ALLOC_DEFAULT
```
    See Also:
    Constant Field Values
  - LOG
```
static final org.apache.commons.logging.Log LOG
```
  - curChunk
```
private AtomicReference<HeapMemStoreLAB.Chunk> curChunk
```
  - chunkQueue
```
private BlockingQueue<HeapMemStoreLAB.Chunk> chunkQueue
```
  - chunkSize
```
final int chunkSize
```
  - maxAlloc
```
final int maxAlloc
```
  - chunkPool
```
private final MemStoreChunkPool chunkPool
```
  - closed
```
private volatile boolean closed
```
  - reclaimed
```
private AtomicBoolean reclaimed
```
  - openScannerCount
```
private final AtomicInteger openScannerCount
```
- Constructor Detail
  - HeapMemStoreLAB
```
public HeapMemStoreLAB()
```
  - HeapMemStoreLAB
```
public HeapMemStoreLAB(org.apache.hadoop.conf.Configuration conf)
```
- Method Detail
  - allocateBytes
```
public ByteRange allocateBytes(int size)
```
    Allocate a slice of the given length. If the size is larger than the maximum size specified for this allocator, returns null.
    
    Specified by:
    
    allocateBytes in interface MemStoreLAB
    
    Returns:
    ByteRange
  - close
```
public void close()
```
    Close this instance since it won't be used any more, try to put the chunks back to pool
    
    Specified by:
    
    close in interface MemStoreLAB
  - incScannerCount
```
public void incScannerCount()
```
    Called when opening a scanner on the data of this MemStoreLAB
    
    Specified by:
    
    incScannerCount in interface MemStoreLAB
  - decScannerCount
```
public void decScannerCount()
```
    Called when closing a scanner on the data of this MemStoreLAB
    
    Specified by:
    
    decScannerCount in interface MemStoreLAB
  - tryRetireChunk
```
private void tryRetireChunk(HeapMemStoreLAB.Chunk c)
```
    Try to retire the current chunk if it is still c. Postcondition is that curChunk.get() != c
    
    Parameters:
    c - the chunk to retire
  - getOrMakeChunk
```
private HeapMemStoreLAB.Chunk getOrMakeChunk()
```
    Get the current chunk, or, if there is no current chunk, allocate a new one from the JVM.
  - getCurrentChunk
```
HeapMemStoreLAB.Chunk getCurrentChunk()
```
  - getChunkQueue
```
BlockingQueue<HeapMemStoreLAB.Chunk> getChunkQueue()
```

Class HeapMemStoreLAB

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

CHUNK_SIZE_KEY

CHUNK_SIZE_DEFAULT

MAX_ALLOC_KEY

MAX_ALLOC_DEFAULT

LOG

curChunk

chunkQueue

chunkSize

maxAlloc

chunkPool

closed

reclaimed

openScannerCount

Constructor Detail

HeapMemStoreLAB

HeapMemStoreLAB

Method Detail

allocateBytes

close

incScannerCount

decScannerCount

tryRetireChunk

getOrMakeChunk

getCurrentChunk

getChunkQueue