聊聊MaxwellKafkaPartitioner

序

本文主要研究一下MaxwellKafkaPartitioner

MaxwellKafkaPartitioner

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/partitioners/MaxwellKafkaPartitioner.java

public class MaxwellKafkaPartitioner extends AbstractMaxwellPartitioner {
	HashFunction hashFunc;

	public MaxwellKafkaPartitioner(String hashFunction, String partitionKey, String csvPartitionColumns, String partitionKeyFallback) {
		super(partitionKey, csvPartitionColumns, partitionKeyFallback);

		int MURMUR_HASH_SEED = 25342;
		switch (hashFunction) {
			case "murmur3": this.hashFunc = new HashFunctionMurmur3(MURMUR_HASH_SEED);
				break;
			case "default":
			default:
				this.hashFunc = new HashFunctionDefault();
				break;
		}
	}

	public int kafkaPartition(RowMap r, int numPartitions) {
		return Math.abs(hashFunc.hashCode(this.getHashString(r)) % numPartitions);
	}
}

• MaxwellKafkaPartitioner继承了AbstractMaxwellPartitioner，其构造器根据hashFunction类型创建HashFunctionMurmur3或者HashFunctionDefault；其kafkaPartition方法则通过Math.abs(hashFunc.hashCode(this.getHashString(r)) % numPartitions)计算partition

AbstractMaxwellPartitioner

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/partitioners/AbstractMaxwellPartitioner.java

public abstract class AbstractMaxwellPartitioner {
	List<String> partitionColumns = new ArrayList<String>();
	private final PartitionBy partitionBy, partitionByFallback;

	private PartitionBy partitionByForString(String key) {


		if ( key == null )
			return PartitionBy.DATABASE;

		switch(key) {
			case "table":
				return PartitionBy.TABLE;
			case "database":
				return PartitionBy.DATABASE;
			case "primary_key":
				return PartitionBy.PRIMARY_KEY;
			case "transaction_id":
				return PartitionBy.TRANSACTION_ID;
			case "column":
				return PartitionBy.COLUMN;
			case "random":
				return PartitionBy.RANDOM;
			default:
				throw new RuntimeException("Unknown partitionBy string: " + key);
		}
	}

	public AbstractMaxwellPartitioner(String partitionKey, String csvPartitionColumns, String partitionKeyFallback) {
		this.partitionBy = partitionByForString(partitionKey);
		this.partitionByFallback = partitionByForString(partitionKeyFallback);

		if ( csvPartitionColumns != null )
			this.partitionColumns = Arrays.asList(csvPartitionColumns.split("\\s*,\\s*"));
	}

	static protected String getDatabase(RowMap r) {
		return r.getDatabase();
	}

	static protected String getTable(RowMap r) {
		return r.getTable();
	}

	public String getHashString(RowMap r, PartitionBy by) {
		switch ( by ) {
			case TABLE:
				String t = r.getTable();
				if ( t == null && partitionByFallback == PartitionBy.DATABASE )
					return r.getDatabase();
				else
					return t;
			case DATABASE:
				return r.getDatabase();
			case PRIMARY_KEY:
				return r.getRowIdentity().toConcatString();
			case TRANSACTION_ID:
				return String.valueOf(r.getXid());
			case COLUMN:
				String s = r.buildPartitionKey(partitionColumns);
				if ( s.length() > 0 )
					return s;
				else
					return getHashString(r, partitionByFallback);
			case RANDOM:
				return RandomStringUtils.random(10, true, true);
		}
		return null; // thx java
	}

	public String getHashString(RowMap r) {
		if ( r.getPartitionString() != null )
			return r.getPartitionString();
		else
			return getHashString(r, partitionBy);
	}
}

• AbstractMaxwellPartitioner的构造器通过partitionByForString确定PartitionBy；其getHashString方法根据PartitionBy返回指定的值

HashFunction

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/partitioners/HashFunction.java

public interface HashFunction {
	int hashCode(String s);
}

• HashFunction接口定义了hashCode方法

HashFunctionDefault

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/partitioners/HashFunctionDefault.java

public class HashFunctionDefault implements HashFunction {
	public int hashCode(String s) {
		return s.hashCode();
	}
}

• HashFunctionDefault实现了HashFunction接口，其hashCode直接返回string的hashCode

HashFunctionMurmur3

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/partitioners/HashFunctionMurmur3.java

public class HashFunctionMurmur3 implements HashFunction {
	private int seed;
	public HashFunctionMurmur3(int seed){
		this.seed = seed;
	}
	public int hashCode(String s) {
		return MurmurHash3.murmurhash3_x86_32(s, 0, s.length(), seed);
	}
}

• HashFunctionMurmur3实现了HashFunction接口，其hashCode方法返回MurmurHash3.murmurhash3_x86_32(s, 0, s.length(), seed)

MaxwellKafkaProducerWorker

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/producer/MaxwellKafkaProducer.java

class MaxwellKafkaProducerWorker extends AbstractAsyncProducer implements Runnable, StoppableTask {
	static final Logger LOGGER = LoggerFactory.getLogger(MaxwellKafkaProducer.class);

	private final Producer<String, String> kafka;
	private final String topic;
	private final String ddlTopic;
	private final MaxwellKafkaPartitioner partitioner;
	private final MaxwellKafkaPartitioner ddlPartitioner;

	//......

	ProducerRecord<String, String> makeProducerRecord(final RowMap r) throws Exception {
		RowIdentity pk = r.getRowIdentity();
		String key = r.pkToJson(keyFormat);
		String value = r.toJSON(outputConfig);
		ProducerRecord<String, String> record;
		if (r instanceof DDLMap) {
			record = new ProducerRecord<>(this.ddlTopic, this.ddlPartitioner.kafkaPartition(r, getNumPartitions(this.ddlTopic)), key, value);
		} else {
			String topic;

			// javascript topic override
			topic = r.getKafkaTopic();
			if ( topic == null ) {
				topic = generateTopic(this.topic, pk);
			}
			LOGGER.debug("context.getConfig().producerPartitionKey = " + context.getConfig().producerPartitionKey);

			record = new ProducerRecord<>(topic, this.partitioner.kafkaPartition(r, getNumPartitions(topic)), key, value);
		}
		return record;
	}

	//......

}

• MaxwellKafkaProducerWorker的makeProducerRecord方法针对DDLMap使用ddlPartitioner.kafkaPartition(r, getNumPartitions(this.ddlTopic))确定partition；非DDLMap的使用partitioner.kafkaPartition(r, getNumPartitions(topic))来确定partition

小结

MaxwellKafkaPartitioner继承了AbstractMaxwellPartitioner，其构造器根据hashFunction类型创建HashFunctionMurmur3或者HashFunctionDefault；其kafkaPartition方法则通过Math.abs(hashFunc.hashCode(this.getHashString(r)) % numPartitions)计算partition

doc

• MaxwellKafkaPartitioner

来源：oschina

链接：https://my.oschina.net/go4it/blog/4270849