org.apache.hadoop.hbase.regionserver

Interface MemStoreLAB

All Known Implementing Classes:

ImmutableMemStoreLAB, MemStoreLABImpl

@InterfaceAudience.Private
public interface MemStoreLAB

A memstore-local allocation buffer.

The MemStoreLAB is basically a bump-the-pointer allocator that allocates big (2MB) chunks from and then doles it out to threads that request slices into the array. These chunks can get pooled as well. See ChunkCreator.

The purpose of this 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.

This manages the large sized chunks. When Cells are to be added to Memstore, MemStoreLAB's copyCellInto(Cell) gets called. This allocates enough size in the chunk to hold this cell's data and copies into this area and then recreate a Cell over this copied data.

See Also:

ChunkCreator

Field Summary

Fields

Modifier and Type	Field and Description
static String	CHUNK_POOL_INITIALSIZE_KEY
static String	CHUNK_POOL_MAXSIZE_KEY
static int	CHUNK_SIZE_DEFAULT
static String	CHUNK_SIZE_KEY
static int	MAX_ALLOC_DEFAULT
static String	MAX_ALLOC_KEY
static String	MSLAB_CLASS_NAME
static float	POOL_INITIAL_SIZE_DEFAULT
static float	POOL_MAX_SIZE_DEFAULT
static boolean	USEMSLAB_DEFAULT
static String	USEMSLAB_KEY

Method Summary

Modifier and Type	Method and Description
void	close() Close 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
Chunk	getNewExternalChunk() Return a new empty chunk without considering this chunk as current The space on this chunk will be allocated externally
void	incScannerCount() Called when opening a scanner on the data of this MemStoreLAB
static boolean	isEnabled(org.apache.hadoop.conf.Configuration conf)
static MemStoreLAB	newInstance(org.apache.hadoop.conf.Configuration conf)

Field Detail

USEMSLAB_KEY

static final String USEMSLAB_KEY

See Also:

Constant Field Values

USEMSLAB_DEFAULT

static final boolean USEMSLAB_DEFAULT

See Also:

Constant Field Values

MSLAB_CLASS_NAME

static final String MSLAB_CLASS_NAME

See Also:

Constant Field Values

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

CHUNK_POOL_MAXSIZE_KEY

static final String CHUNK_POOL_MAXSIZE_KEY

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Constant Field Values

CHUNK_POOL_INITIALSIZE_KEY

static final String CHUNK_POOL_INITIALSIZE_KEY

See Also:

Constant Field Values

POOL_MAX_SIZE_DEFAULT

static final float POOL_MAX_SIZE_DEFAULT

See Also:

Constant Field Values

POOL_INITIAL_SIZE_DEFAULT

static final float POOL_INITIAL_SIZE_DEFAULT

See Also:

Constant Field Values

Method Detail

copyCellInto

Cell copyCellInto(Cell cell)

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.

close

void close()

Close instance since it won't be used any more, try to put the chunks back to pool

incScannerCount

void incScannerCount()

Called when opening a scanner on the data of this MemStoreLAB

decScannerCount

void decScannerCount()

Called when closing a scanner on the data of this MemStoreLAB

getNewExternalChunk

Chunk getNewExternalChunk()

Return a new empty chunk without considering this chunk as current The space on this chunk will be allocated externally

newInstance

static MemStoreLAB newInstance(org.apache.hadoop.conf.Configuration conf)

isEnabled

static boolean isEnabled(org.apache.hadoop.conf.Configuration conf)