org.apache.hadoop.hbase.regionserver

Class MemStoreLAB

java.lang.Object

org.apache.hadoop.hbase.regionserver.MemStoreLAB

@InterfaceAudience.Private
public class MemStoreLAB
extends Object

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
static class	MemStoreLAB.Allocation The result of a single allocation.

Constructor Summary

Constructors

Constructor and Description
MemStoreLAB()
MemStoreLAB(org.apache.hadoop.conf.Configuration conf, MemStoreChunkPool pool)

Method Summary

Methods

Modifier and Type	Method and Description
MemStoreLAB.Allocation	allocateBytes(int size) Allocate a slice of the given length.

Methods inherited from class java.lang.Object

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

Constructor Detail

MemStoreLAB

public MemStoreLAB()

MemStoreLAB

public MemStoreLAB(org.apache.hadoop.conf.Configuration conf,
           MemStoreChunkPool pool)

Method Detail

allocateBytes

public MemStoreLAB.Allocation 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.