Journaling – Getting Started

Java

1.7 and UP.

It uses NIO File channels for cache write backs to disk. Hence dependency on 1.7.

POM

<dependency>
    <groupId>org.wonderdb.journaling</groupId>
    <artifactId>journaling</artifactId>
    <version>0.1</version>
</dependency>

Github location

https://github.com/dreamdbvilas/wonderdbjournaling.git

Design and How it works

Please refer to my blog page on journaling to understand design and how it works.

Configuration

Since there are not too mane configuration parameters for this module, You just need to pass these as a parameter to init method. Below section describes how to use it in the code.

Here are the parameters you can control.

logFolders[]

You can provide list of folders to store redo log files. If you have more than one disk then it is good idea to provide more than one log file folder from different disks. This will improve performance and throughput due to reduced disk contention.

maxRedoLogFileSize

Maximum redo log file size before log files are rotated. Based on your transaction volume or redo log file generation volume set it to some value. You can start with 100K to 2M.

applyType

This enum has following values

Every

Apply every redo log/transaction to backend data files.

SoOften

Similar to every, except it applies every so often depending on applyFrequency parameter.

OnLogSwitch

Apply changes on log switch. This is the best option if you have more than one disk and you have provided with more than one redo log folder.

None

Sometimes applications don’t want this module to apply changes to data files. In that case set this value to None.

WonderDB uses this setting since it applies data file changes from caches.

applyFrequency

This value is meaningful only if you have set applyType = SoOften.

Supporten APIs

Using it in the Code

Initialization

Call this first in the code during initialization of the app.

LogManager.getInistance.init(String[] logFolders, int maxFileSize, applyType, int applyFrequency);

Using it in the code

// start a transaction
TransactionId txnId = LogManager.getInstance().startTxn();

// logging in transaction
ChannelBuffer buffer = ChannelBuffers.wrappedBuffer("My First Txn Entry".getBytes());
LogManager.getInstance().log(txnId, "dataFile1", 10, buffer);

buffer = ChannelBuffers.wrappedBuffer("My First Txn second entry".getBytes());
LogManager.getInstance().log(txnId, "dataFile2", 1000, buffer);

// commit
LogManager.getInstance().commit(txnId);

// To rollback a txn call
LogManager.getInstance().rollback(txnId);

Shutdown

Call following line during the shutdown at the end. It cleans up all resources like thread pools, caches, sockets etc. JVM will not exit properly if this line is not called during shutdown.

LogManager.getInstance().shutdown();

Questions?

Post you question on WonderDBCache google group.