MemStoreLAB (Apache HBase 2.5.0 API)

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 float`	`INDEX_CHUNK_SIZE_PERCENTAGE_DEFAULT`
`static String`	`INDEX_CHUNK_SIZE_PERCENTAGE_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

All Methods Static Methods Instance Methods Abstract Methods Default Methods
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
`Cell`	`forceCopyOfBigCellInto(Cell cell)` Allocates slice in this LAB and copy the passed Cell into this area.
`Chunk`	`getNewExternalChunk(ChunkCreator.ChunkType chunkType)`
`Chunk`	`getNewExternalChunk(int size)`
`void`	`incScannerCount()` Called when opening a scanner on the data of this MemStoreLAB
`static boolean`	`isEnabled(org.apache.hadoop.conf.Configuration conf)`
`boolean`	`isOffHeap()`
`boolean`	`isOnHeap()`
`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
  - INDEX_CHUNK_SIZE_PERCENTAGE_KEY
```
static final String INDEX_CHUNK_SIZE_PERCENTAGE_KEY
```
    See Also:
    
    Constant Field Values
  - INDEX_CHUNK_SIZE_PERCENTAGE_DEFAULT
```
static final float INDEX_CHUNK_SIZE_PERCENTAGE_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
```
    See Also:
    
    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.
  - forceCopyOfBigCellInto
```
Cell forceCopyOfBigCellInto(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. Since the process of flattening to CellChunkMap assumes all cells are allocated on MSLAB, and since copyCellInto does not copy big cells (for whom size > maxAlloc) into MSLAB, this method is called while the process of flattening to CellChunkMap is running, for forcing the allocation of big cells on this MSLAB.
  - 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(ChunkCreator.ChunkType chunkType)
```
  - getNewExternalChunk
```
Chunk getNewExternalChunk(int size)
```
  - newInstance
```
static MemStoreLAB newInstance(org.apache.hadoop.conf.Configuration conf)
```
  - isEnabled
```
static boolean isEnabled(org.apache.hadoop.conf.Configuration conf)
```
  - isOnHeap
```
boolean isOnHeap()
```
  - isOffHeap
```
boolean isOffHeap()
```

Interface MemStoreLAB

Field Summary

Method Summary

Field Detail

USEMSLAB_KEY

USEMSLAB_DEFAULT

MSLAB_CLASS_NAME

CHUNK_SIZE_KEY

CHUNK_SIZE_DEFAULT

INDEX_CHUNK_SIZE_PERCENTAGE_KEY

INDEX_CHUNK_SIZE_PERCENTAGE_DEFAULT

MAX_ALLOC_KEY

MAX_ALLOC_DEFAULT

CHUNK_POOL_MAXSIZE_KEY

CHUNK_POOL_INITIALSIZE_KEY

POOL_MAX_SIZE_DEFAULT

POOL_INITIAL_SIZE_DEFAULT

Method Detail

copyCellInto

forceCopyOfBigCellInto

close

incScannerCount

decScannerCount

getNewExternalChunk

getNewExternalChunk

newInstance

isEnabled

isOnHeap

isOffHeap