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 (2MB by default) regions and then doles them out to threads that request 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.DataReclaimer, MemtableAllocator.SubAllocator

Field Summary

Fields inherited from class org.apache.cassandra.utils.memory.MemtableAllocator

NO_OP

Method Summary

Methods

Modifier and Type	Method and Description
java.nio.ByteBuffer	allocate(int size)
java.nio.ByteBuffer	allocate(int size, OpOrder.Group opGroup)
protected AbstractAllocator	allocator(OpOrder.Group writeOp)
MemtableAllocator.DataReclaimer	reclaimer()
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

clone, clone, clone, clone, clone

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

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

reclaimer

public MemtableAllocator.DataReclaimer reclaimer()

Specified by:

reclaimer in class MemtableAllocator

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

allocator

protected AbstractAllocator allocator(OpOrder.Group writeOp)

Overrides:

allocator in class MemtableBufferAllocator