聊聊rocketmq的AllocateMessageQueueAveragely

序

本文主要研究一下rocketmq的AllocateMessageQueueAveragely

AllocateMessageQueueStrategy

rocketmq-client-4.5.2-sources.jar!/org/apache/rocketmq/client/consumer/AllocateMessageQueueStrategy.java

public interface AllocateMessageQueueStrategy {

    /**
     * Allocating by consumer id
     *
     * @param consumerGroup current consumer group
     * @param currentCID current consumer id
     * @param mqAll message queue set in current topic
     * @param cidAll consumer set in current consumer group
     * @return The allocate result of given strategy
     */
    List<MessageQueue> allocate(
        final String consumerGroup,
        final String currentCID,
        final List<MessageQueue> mqAll,
        final List<String> cidAll
    );

    /**
     * Algorithm name
     *
     * @return The strategy name
     */
    String getName();
}

• AllocateMessageQueueStrategy定义了allocate、getName方法

AllocateMessageQueueAveragely

rocketmq-client-4.5.2-sources.jar!/org/apache/rocketmq/client/consumer/rebalance/AllocateMessageQueueAveragely.java

public class AllocateMessageQueueAveragely implements AllocateMessageQueueStrategy {
    private final InternalLogger log = ClientLogger.getLog();

    @Override
    public List<MessageQueue> allocate(String consumerGroup, String currentCID, List<MessageQueue> mqAll,
        List<String> cidAll) {
        if (currentCID == null || currentCID.length() < 1) {
            throw new IllegalArgumentException("currentCID is empty");
        }
        if (mqAll == null || mqAll.isEmpty()) {
            throw new IllegalArgumentException("mqAll is null or mqAll empty");
        }
        if (cidAll == null || cidAll.isEmpty()) {
            throw new IllegalArgumentException("cidAll is null or cidAll empty");
        }

        List<MessageQueue> result = new ArrayList<MessageQueue>();
        if (!cidAll.contains(currentCID)) {
            log.info("[BUG] ConsumerGroup: {} The consumerId: {} not in cidAll: {}",
                consumerGroup,
                currentCID,
                cidAll);
            return result;
        }

        int index = cidAll.indexOf(currentCID);
        int mod = mqAll.size() % cidAll.size();
        int averageSize =
            mqAll.size() <= cidAll.size() ? 1 : (mod > 0 && index < mod ? mqAll.size() / cidAll.size()
                + 1 : mqAll.size() / cidAll.size());
        int startIndex = (mod > 0 && index < mod) ? index * averageSize : index * averageSize + mod;
        int range = Math.min(averageSize, mqAll.size() - startIndex);
        for (int i = 0; i < range; i++) {
            result.add(mqAll.get((startIndex + i) % mqAll.size()));
        }
        return result;
    }

    @Override
    public String getName() {
        return "AVG";
    }
}

• AllocateMessageQueueAveragely实现了AllocateMessageQueueStrategy接口，其getName返还AVG，其allocate方法首先计算index(cidAll.indexOf(currentCID))，然后计算mod(mqAll.size() % cidAll.size())
• 之后计算averageSize，若mqAll.size()小于等于cidAll.size()则取1，否则取mod > 0 && index < mod ? mqAll.size() / cidAll.size() + 1 : mqAll.size() / cidAll.size()
• 最后计算startIndex((mod > 0 && index < mod) ? index * averageSize : index * averageSize + mod)及range(Math.min(averageSize, mqAll.size() - startIndex))；之后按range进行循环，将下标为(startIndex + i) % mqAll.size()的消息添加到result

小结

AllocateMessageQueueAveragely实现了AllocateMessageQueueStrategy接口，其getName返还AVG，其allocate方法按range进行循环，将下标为(startIndex + i) % mqAll.size()的消息添加到result

doc

• AllocateMessageQueueAveragely