org.apache.hadoop.hbase.regionserver

Class HeapMemStoreLAB

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

Constructor Summary

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
void	incScannerCount() Called when opening a scanner on the data of this MemStoreLAB

Methods inherited from class java.lang.Object

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

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