用于JVM的高性能持久LSM key-value存儲庫：HeftyDB

HeftyDB是一個用于JVM的高性能持久LSM key-value存儲庫。它的設計充分考慮了以下目標：

1. Be as fast and memory efficient as is feasible on the JVM for random reads, random writes, and range scans.
2. Provide a stable base on which to build new and interesting storage systems.
3. Provide detailed metrics about what is going on at every level of the stack.
4. Have clean, understandable code that others can learn from.
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特性

Simple API

Supports gets and puts by key as well as ascending and descending iteration from any key.

Log Structured Merge Trees

All write operations are sequential, and are limited by the sequential IO performance of the underlying disk. Tables are written with a full B+tree index for memory efficiency, even at very large table sizes.

Snapshotted multi-version concurrency control

Reads and range scans never block writes.

Off-heap data structures

Operations in the critical read and write paths are implemented using off-heap memory wherever possible to reduce GC pressure and memory overhead.

Multi-threaded compactions

Make use of multiple CPU cores for table writes and table compactions

Pluggable compaction strategies

Provide custom compaction behavior tailored to specific workloads.

try {
    //Open a HeftyDB in a directory
    DB testDB = HeftyDB.open(new Config.Builder().directory(directory).build());

    //Write a key
    Snapshot snapshot = testDB.put(someByteBufferKey, someByteBufferValue);

    //Read a key at a particular snapshot
    Record record = testDB.get(someByteBufferKey, snapshot);

    //Delete a key
    Snapshot deleteSnapshot = testDB.delete(someByteBufferKey);

    //Get an ascending iterator of keys greater than or equal
    //to the provided key at the provided snapshot
    CloseableIterator<Record> ascendingIterator = testDB.ascendingIterator(someByteBufferKey, snapshot);
    while (ascendingIterator.hasNext()){
        Record next = ascendingIterator.next();
    }

    //Get a descending iterator of keys less than or equal
    //to the provided key at the provided snapshot
    CloseableIterator<Record> descendingIterator = testDB.descendingIterator(someByteBufferKey, snapshot);
    while (descendingIterator.hasNext()){
        Record next = descendingIterator.next();
    }

    //Compact the database
    Future<?> compactionFuture = testDB.compact();
    compactionFuture.get();

    //Close the database
    testDB.close();
} catch (IOException e){
    Logger.error(e);
}

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