org.apache.hadoop.hbase.regionserver

Class MemStoreLABImpl

java.lang.Object

org.apache.hadoop.hbase.regionserver.MemStoreLABImpl

All Implemented Interfaces:

MemStoreLAB

@InterfaceAudience.Private
public class MemStoreLABImpl
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 Cells 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. The chunks created by this MemStoreLAB can get pooled at ChunkCreator. When the Chunk comes from pool, it can be either an on heap or an off heap backed chunk. The chunks, which this MemStoreLAB creates on its own (when no chunk available from pool), those will be always on heap backed.

Field Summary

Fields inherited from interface org.apache.hadoop.hbase.regionserver.MemStoreLAB

CHUNK_POOL_INITIALSIZE_KEY, CHUNK_POOL_MAXSIZE_KEY, CHUNK_SIZE_DEFAULT, CHUNK_SIZE_KEY, INDEX_CHUNK_PERCENTAGE_DEFAULT, INDEX_CHUNK_PERCENTAGE_KEY, MAX_ALLOC_DEFAULT, MAX_ALLOC_KEY, MSLAB_CLASS_NAME, POOL_INITIAL_SIZE_DEFAULT, POOL_MAX_SIZE_DEFAULT, USEMSLAB_DEFAULT, USEMSLAB_KEY

Constructor Summary

Constructors

Constructor and Description
MemStoreLABImpl()
MemStoreLABImpl(org.apache.hadoop.conf.Configuration conf)

Method Summary

Modifier and Type	Method and Description
void	close() Close this instance since it won't be used any more, try to put the chunks back to pool
Cell	copyCellInto(Cell cell) Allocates slice in this LAB and copy the passed Cell into this area.
void	decScannerCount() Called when closing a scanner on the data of this MemStoreLAB
Cell	forceCopyOfBigCellInto(Cell cell) When a cell's size is too big (bigger than maxAlloc), copyCellInto does not allocate it on MSLAB.
Chunk	getNewExternalChunk(ChunkCreator.ChunkType chunkType)
Chunk	getNewExternalChunk(int size)
void	incScannerCount() Called when opening a scanner on the data of this MemStoreLAB
boolean	isOffHeap()
boolean	isOnHeap()

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.hbase.regionserver.MemStoreLAB

isEnabled, newInstance

Constructor Detail

MemStoreLABImpl

public MemStoreLABImpl()

MemStoreLABImpl

public MemStoreLABImpl(org.apache.hadoop.conf.Configuration conf)

Method Detail

copyCellInto

public Cell copyCellInto(Cell cell)

Description copied from interface: MemStoreLAB

Allocates slice in this LAB and copy the passed Cell into this area. Returns new Cell instance over the copied the data. When this MemStoreLAB can not copy this Cell, it returns null.

Specified by:

copyCellInto in interface MemStoreLAB

forceCopyOfBigCellInto

public Cell forceCopyOfBigCellInto(Cell cell)

When a cell's size is too big (bigger than maxAlloc), copyCellInto does not allocate it on MSLAB. Since the process of flattening to CellChunkMap assumes that all cells are allocated on MSLAB, during this process, the big cells are copied into MSLAB using this method.

Specified by:

forceCopyOfBigCellInto in interface MemStoreLAB

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

getNewExternalChunk

public Chunk getNewExternalChunk(ChunkCreator.ChunkType chunkType)

Specified by:

getNewExternalChunk in interface MemStoreLAB

getNewExternalChunk

public Chunk getNewExternalChunk(int size)

Specified by:

getNewExternalChunk in interface MemStoreLAB

isOnHeap

public boolean isOnHeap()

Specified by:

isOnHeap in interface MemStoreLAB

isOffHeap

public boolean isOffHeap()

Specified by:

isOffHeap in interface MemStoreLAB