KVStore

KVStore is a Key-Value Store based on B+Tree for Memory & Disk (for on disk, keys and values must be fixed length) for Java. Project is Open source (Apache License, Version 2.0)

API is similar to TreeMap.

Current Stable Version is 1.0.2

DOC

Usage Example

import java.util.Iterator;
import org.javastack.kvstore.KVStoreFactory;
import org.javastack.kvstore.Options;
import org.javastack.kvstore.holders.IntHolder;
import org.javastack.kvstore.structures.btree.BplusTree.TreeEntry;
import org.javastack.kvstore.structures.btree.BplusTreeFile;

public class Example {
	private static final String btreeFile = "/tmp/test";

	//
	public static void main(final String[] args) throws Exception {
		final int[] keys = new int[] { 5, 7, -11, 111, 0 };
		//
		KVStoreFactory<IntHolder, IntHolder> factory = new KVStoreFactory<IntHolder, IntHolder>(
				IntHolder.class, IntHolder.class);
		Options opts = factory.createTreeOptionsDefault()
				.set(KVStoreFactory.FILENAME, btreeFile);
		BplusTreeFile<IntHolder, IntHolder> tree = factory.createTreeFile(opts);
		//
		// Open & Recovery tree if needed
		try {
			if (tree.open())
				System.out.println("open tree ok");
		} catch (InvalidDataException e) {
			System.out.println("open tree error, recovery needed");
			if (tree.recovery(false) && tree.open()) {
				System.out.println("recovery ok, tree opened");
			} else {
				throw new Exception("Fatal Error Opening Tree");
			}
		}
		// clear all previous content if any
		tree.clear();
		// ============== PUT
		for (int i = 0; i < keys.length; i++) {
			final IntHolder key = IntHolder.valueOf(keys[i]);
			final IntHolder value = IntHolder.valueOf(i);
			tree.put(key, value);
		}
		tree.sync();
		// ============== GET
		System.out.println("tree.get(7)=" + tree.get(IntHolder.valueOf(7)));
		// ============== REMOVE
		tree.remove(IntHolder.valueOf(7));
		// ============== ITERATOR
		for (Iterator<TreeEntry<IntHolder, IntHolder>> i = tree.iterator(); i
				.hasNext();) {
			TreeEntry<IntHolder, IntHolder> e = i.next();
			System.out.println("Key=" + e.getKey() + " Value=" + e.getValue());
		}
		// ============== FIRST / LAST
		System.out.println("tree.firstKey()=" + tree.firstKey());
		System.out.println("tree.lastKey()=" + tree.lastKey());
		//
		tree.sync();
		tree.close();
	}
}

The Result:

tree.get(7)=1
Key=-11 Value=2
Key=0 Value=4
Key=5 Value=0
Key=111 Value=3
tree.firstKey()=-11
tree.lastKey()=111

• More examples in Test package

MAVEN

Add the KVStore dependency to your pom.xml:

<dependency>
    <groupId>org.javastack</groupId>
    <artifactId>kvstore</artifactId>
    <version>1.0.2</version>
</dependency>

TODOs

• A lot of Doc
• Describe disk formats
• HashMap on disk
• Separate size of read cache and write cache

DONEs

• BlockStore (Fixed length chunks)
  • Support for mmaped files
• StreamStore (Variable length chunks)
• B+Tree for Index
  • Buffer reuse
  • Memory mode
  • Persistence on disk (BlockStore)
    • Cache of nodes
    • Reuse free blocks on disk
    • Redo log
    • Recovery system
    • Allow open without populate read cache
    • Allow open readOnly mode
    • File locking (multi-process)
• HashMaps for natives (memory)
• Holders for data and NIO serialization
  • Fixed length
    • Boolean
    • Byte
    • Short
    • Integer
    • Long
    • Null
  • Variable length
    • Strings
• Create Factory
• Options object for factory
• Use Log4J
• Maven repository

MISC

Benchmarks

Values are not accurate, but orientative. Higher better. All test Running on Laptop { Windows Vista (32bits), Core 2 Duo 1.4Ghz (U9400), 4GB Ram, Magnetic Disk (WDC-WD5000BEVT-22ZAT0) }.

Test-1 (org.javastack.kvstore.test.BenchMarkDiskStore): Registry { count=1e6, datalen=256bytes } BlockStore { blockSize=512 (2reg/block), fileSize=250MB } StreamStore { outBufferSize=0x10000, align=true, fileSize=256MB }

Test-2 (org.javastack.kvstore.test.BenchMarkMemoryStructures): Registry { count=2e6, datalen=256bytes } BplusTreeMemory { key=Integer, b-order=511 } IntHashMap { initialSize=(2e6 * 2) }

Inspired in Book: Open Data Structures in Java, Perl DB_File, JDBM3 and H2-Database, this code is Java-minimalistic version.