offheap-store's Introduction

OffHeap Store

OffHeap Store is a library that provides a set of map and cache implementations that store data outside of the normal Java heap. Additionally it provides a bunch of interesting things to support these functions that might be interesting in isolation to some people.

Licensed under the Apache License, Version 2.0 © Terracotta, Inc., a Software AG company.

http://www.terracotta.org

Status of the build:

What’s Available

On the surface OffHeap Store contains implementations of:

Map (non thread-safe)
ConcurrentMap (single stripe or segmented; read-write locked or exclusively locked)
Set (but use Collections.newSetFromMap(Map) instead)
Clock Cache (single stripe or segmented; read-write locked or exclusively locked)

Additional functionality includes:

Cache Entry Pinning
Eviction Listeners
Non-fault tolerant disk backend

Things that might be interesting to some:

Per entry metadata (very basic API)
Serialization optimization (redundant ObjectStreamClass descriptor compression)
Native heap-alike implementation (OffHeapStorageArea)
A (crude) weak identity hash map (because the world needed one more)

Structure

Like all software OffHeap Store is just a big stack of abstractions, rough structure starting at the bottom and working up.

BufferSource	ByteBuffer factories [org.terracotta.offheapstore.buffersource]
PageSource	Page factories, that uses ByteBuffers) [org.terracotta.offheapstore.paging]
OffHeapStorageArea	native heap-alike that uses pages)
StorageEngine	provide storage for POJOs, some use OffHeapStorageArea)
OffHeapHashMap	core map implementation, uses storage engine for K/V storage and a page for the hashtable.
a million subclasses	all the map derivatives: concurrent, evicting (caches), et al.