SlabAllocator (apache-cassandra API)

java.lang.Object
- org.apache.cassandra.utils.memory.MemtableAllocator
- - org.apache.cassandra.utils.memory.MemtableBufferAllocator
  - - org.apache.cassandra.utils.memory.SlabAllocator

```
public class SlabAllocator
extends MemtableBufferAllocator
```
+ * The SlabAllocator is a bump-the-pointer allocator that allocates + * large (1MiB) global regions and then doles them out to threads that + * request smaller sized (up to 128KiB) slices into the array.
The purpose of this class is to combat heap fragmentation in long lived objects: by ensuring that all allocations with similar lifetimes only to large regions of contiguous memory, we ensure that large blocks get freed up at the same time.
Otherwise, variable length byte arrays allocated end up interleaved throughout the heap, and the old generation gets progressively more fragmented until a stop-the-world compacting collection occurs.

Nested Class Summary
- Nested classes/interfaces inherited from class org.apache.cassandra.utils.memory.MemtableAllocator
  MemtableAllocator.SubAllocator

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.nio.ByteBuffer`	`allocate(int size)`
`java.nio.ByteBuffer`	`allocate(int size, OpOrder.Group opGroup)`
`Cloner`	`cloner(OpOrder.Group writeOp)`
`EnsureOnHeap`	`ensureOnHeap()`
`void`	`setDiscarded()`	Indicate the memory and resources owned by this allocator are no longer referenced, and can be reclaimed/reused.

Methods inherited from class org.apache.cassandra.utils.memory.MemtableBufferAllocator
allocator

Methods inherited from class org.apache.cassandra.utils.memory.MemtableAllocator
isLive, offHeap, onHeap, setDiscarding

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - ensureOnHeap
```
public EnsureOnHeap ensureOnHeap()
```
    Specified by:
    
    ensureOnHeap in class MemtableAllocator
  - allocate
```
public java.nio.ByteBuffer allocate(int size)
```
  - allocate
```
public java.nio.ByteBuffer allocate(int size,
                                    OpOrder.Group opGroup)
```
    Specified by:
    
    allocate in class MemtableBufferAllocator
  - setDiscarded
```
public void setDiscarded()
```
    Description copied from class: MemtableAllocator
    
    Indicate the memory and resources owned by this allocator are no longer referenced, and can be reclaimed/reused.
    
    Overrides:
    
    setDiscarded in class MemtableAllocator
  - cloner
```
public Cloner cloner(OpOrder.Group writeOp)
```
    Specified by:
    
    cloner in class MemtableAllocator