org.apache.hadoop.hbase.regionserver

Interface MemStoreLAB

All Known Implementing Classes:

HeapMemStoreLAB

@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.

The purpose of this 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.

Method Summary

Modifier and Type	Method and Description
ByteRange	allocateBytes(int size) Allocate a slice of the given length.
void	close() Close 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

Method Detail

allocateBytes

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.

Parameters:

size -

Returns:

ByteRange

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