Streamers Implementation Guidelines

Overview

This guide describes how to implement custom data streamer and describes basic concepts and implementation details.

It is useful to take a look at:

• SocketStreamer - reference implementation of custom data streamer as TCP socket server.
• WordsSocketStreamerServer and WordsSocketStreamerClient - example of SocketStreamer usage.

Basic Concepts

The purpose of streamers is data ingesting from various sources (e.g. TCP socket or Kafka) and streaming them into Ignite cache for further processing. Ignite provides IgniteDataStreamer API that allows stream data into cache and convenient StreamAdapter that wraps data streamer instance and provides basis for custom streamer implementation.

Data stream consists of messages that can be represented as Java objects of some type that should be converted to cache entries (key-value pairs or tuples). StreamTupleExtractor is responsible for such conversion.

The following parts of custom data streamer are missing and should be implemented by developer:

• conversion of stream specific messages to Java object (e.g. byte array to String);
• stream wrapper that encapsulates functionality related with particular data source.

From connection initiating stand point data streamer can be implemented as a server or a client with respect of data source and requirements. For example, HTTP data streamer implemented as a client can request the data from external web services. On the other hand, HTTP data streamer implemented as a server can process a large number of request from external HTTP clients.

In order to implement custom data streamer a developer should optionally extend StreamAdapter class, add functionality related with particular data source and streamer life cycle logic if needed. As mentioned above StreamAdapter wraps IgniteDataStreamer instance and also needs StreamTupleExtractor instance, that could be provided via constructor or corresponding setters.

The central StreamAdapater's method is addMessage(T msg) that just converts message to cache entry using StreamTupleExtractor and streams entry into cache. This method doesn't block current thread due to the nature of IgniteDataStreamer.

StreamTupleExtractor interface expose the extract(T msg) method that returns a cache entry as Map.Entry<K, V> instance. For example, if message represents a string with two values that separated by '=' symbol where left part is a word and right one - integer number, then extractor could be implemented as:

public class WordCountTupleExtractor implements StreamTupleExtractor<String, String, Integer> {

	 @Override public Map.Entry<String, Integer> extract(String msg) {
        String[] tokens = msg.split("=");

 		return new IgniteBiTuple<>(tokens[0], Integer.valueOf(tokens[1]));
    }
}

Streamer Life Cycle

Streamer life cycle depends on chosen implementation model (server or client) and requirements. Usually streamer can be in one of the following states: created, initialized, shutdown and may be one of transition states. StreamAdapter doesn't provide any life cycle managements methods. Correct life cycle management implementation is completely responsibility of data streamer developer.

So far as data streamer requires IgniteDataStreamer instance, Ignite node with a cache should be started and IgniteDataStreamer should be obtained. Note that StreamAdapter doesn't manage by IgniteDataStreamer life cycle.

The following code snippet demonstrates correct data streamer initialization assuming that there is CustomStreamer implementation with start method:

// Start Ignite node with default configuration.

Ignite ignite = Ignition.start();

// Create and start cache with default configuration and name "wordsCache".

IgniteCache<String, Integer> cache = ignite.getOrCreateCache("wordsCache");

// Get data streamer reference for cache with name "wordsCache".

IgniteDataStreamer<String, Integer> stmr = ignite.dataStreamer("wordsCache");

// Create custom data streamer implementation.

CustomStreamer customStmr = new CustomStreamer(stmr, new WordCountTupleExtractor());

// Start custom data streamer if it provides corresponding methods.

customStmr.start();

Reference Implementation

Ignite provides SocketStreamer - reference custom data streamer implementation. SocketStreamer is NIO-based TCP socket server that accepts client connections on configured port, receives data represented as bytes array, converts it to user defined type using SocketMessageConverter and streams it into cache.

The default SocketMessageConverter implementation uses standard Java serialization/deserialization mechanism assuming that data stream contains serialized Java objects.

SocketStreamer supports two communication protocols:

• message size based protocol (default) where each message in the stream is prepended by 4-byte integer header containing message size;
• message delimiter based protocol where each message in the stream is appended with user defined delimiter (see SocketStreamer.setDelimiter(byte[] delim) method).

SocketStreamer implementation has two life cycle management start and stop methods that initialize and shutdown TCP socket server respectively.

The following code snippet demonstrates

Implementation Tips