cojen/TuplDB

The Unnamed Persistence Library

Tupl is a high-performance, concurrent, transactional, scalable, low-level embedded database. Features include record-level locking, upgradable locks, deadlock detection, cursors, hot backups, striped files, encryption, replication, compression, nested transaction scopes, direct lock control, sorting, views, filters, transforms, unions, intersections, and full memory mapped support.

• Javadocs
• FAQ
• Replication

Tupl can be used directly, or it can be used for implementing a high-level database. Tupl is powerful enough for supporting all the requirements of relational SQL databases as well as NoSQL databases. Because Tupl doesn't impose any structure or encoding for data, a high-level database is free to implement the most efficient format it requires.

The main entry point is the Database class. Here is a simple example for opening a non-durable database:

var config = new DatabaseConfig().maxCacheSize(100_000_000);
Database db = Database.open(config);

To open a durable database, a base file path must be provided. Database files are created using the base as a prefix.

var config = new DatabaseConfig()
    .baseFilePath("/var/lib/tupl")
    .cacheSize(100_000_000)
    .durabilityMode(DurabilityMode.NO_FLUSH);

Database db = Database.open(config);

Notice that a fixed cache size is set, and also notice the durability mode. A weak durability mode improves the performance of transactional changes, by not immediately flushing those changes to the underlying files.

Setting a fixed cache size is generally preferred over setting a maximum size, because it pre-allocates the cache when the Database is opened. This allows any heap size limits to be detected early, yielding an OutOfMemoryError. The default cache size is 1000 pages, and the default page size is 4096 bytes.

Basic operations

A Tupl database manages a collection of indexes, which are ordered mappings of byte[] keys to byte[] values.

Database db = ...

// Open an index, creating it if necessary.
Index userIx = db.openIndex("user");

Indexes offer a low-level representation of data, and so applications which use them directly are responsible for performing their own encoding.

// Store a user in an auto-commit transaction.
User user = ...
byte[] userKey = encodeUserKey(user);
byte[] userValue = encodeUserValue(user);
userIx.store(null, userKey, userValue);

To bundle multiple operations together, specify an explicit transaction:

Index userByNameIx = ...

byte[] userNameKey = encodeUserName(user);

Transaction txn = db.newTransaction();
try {
    userIx.store(txn, userKey, userValue);
    userByNameIx.store(txn, userNameKey, userKey);
    txn.commit();
} finally {
    txn.reset();
}

Entries can retrieved by loading them directly, or via a cursor:

// Find all users whose last name starts with 'J'.
byte[] startKey = encodeUserName("J");
byte[] endKey = encodeUserName("K");

// Open a new cursor with an auto-commit transaction.
Cursor namesCursor = userByNameIx.newCursor(null);
try {
    // Find names greater than or equal to the start key.
    namesCursor.findGe(startKey);
    byte[] nameKey;
    while ((nameKey = namesCursor.key()) != null) {
        byte[] userKey = namesCursor.value();
        ...

        // Move to next name, while still being less than the end key.
        namesCursor.nextLt(endKey);
    }
} finally {
    namesCursor.reset();
}

The above example can also be implemented using a sub-view:

// View all users whose last name starts with 'J'.
View userByNameView = userByNameIx.viewPrefix(startKey, 0);

// Scan the entire view of names.
Cursor namesCursor = userByNameView.newCursor(null);
try {
    namesCursor.first();
    byte[] nameKey;
    while ((nameKey = namesCursor.key()) != null) {
        byte[] userKey = namesCursor.value();
        ...

        namesCursor.next();
    }
} finally {
    namesCursor.reset();
}