一個快速，易于使用的Java嵌入式數據庫引擎：MapDB
MapDB提供了并發的Maps，Sets 和 Queues，基于磁盤存儲或off-heap-memory。這是一個快速，可擴展的和易于使用的嵌入式Java數據庫引擎。非常微小（jar只有160KB），但功能強大，如事務，空間高效的序列化，實例緩存和透明壓縮/加密。
功能特性：
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并發 - MapDB has record level locking and state-of-art concurrent engine. Its performance scales nearly linearly with number of cores. Data can be written by multiple parallel threads.
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快速 - MapDB has outstanding performance rivaled only by native DBs. It is result of more than a decade of optimizations and rewrites.
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ACID事務 - MapDB optionally supports ACID transactions with full MVCC isolation. MapDB uses write-ahead-log or append-only store for great write durability.
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靈活 - MapDB can be used everywhere from in-memory cache to multi-terabyte database. It also has number of options to trade durability for write performance. This makes it very easy to configure MapDB to exactly fit your needs.
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Hackable - MapDB is component based, most features (instance cache, async writes, compression) are just class wrappers. It is very easy to introduce new functionality or component into MapDB.
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SQL Like - MapDB was developed as faster alternative to SQL engine. It has number of features which makes transition from relational database easier: secondary indexes/collections, autoincremental sequential ID, joints, triggers, composite keys...
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低磁盤空間使用情況 - MapDB has number of features (serialization, delta key packing...) to minimize disk used by its store. It also has very fast compression and custom serializers. We take disk-usage seriously and do not waste single byte.
import org.mapdb.*;
//Configure and open database using builder pattern.
DB db = DBMaker
.newFileDB(new File("testdb"))
.closeOnJvmShutdown()
.make();
//create new collection (or open existing)
ConcurrentNavigableMap map = db.getTreeMap("collectionName");
map.put(1,"one");
map.put(2,"two");
//persist changes into disk, there is also rollback() method
db.commit();
db.close();