Package org.apache.cassandra.utils.memory

Class SlabAllocator

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

Modifier and Type	Method	Description
ByteBuffer	allocate(int size)
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 Details

ensureOnHeap

public EnsureOnHeap ensureOnHeap()

Specified by:

ensureOnHeap in class MemtableAllocator

allocate

public ByteBuffer allocate(int size)

allocate

public 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