[jira] [Commented] (ROCKETMQ-136) Provide a handy message queue producer for order message sharding

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ROCKETMQ-136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16174136#comment-16174136 ] 

ASF GitHub Bot commented on ROCKETMQ-136:
-----------------------------------------

Github user dongeforever commented on a diff in the pull request:

    https://github.com/apache/incubator-rocketmq/pull/149#discussion_r140136764
  
    --- Diff: client/src/main/java/org/apache/rocketmq/client/producer/selector/SelectMessageQueueByConsistentHash.java ---
    @@ -0,0 +1,94 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
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    + *
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    + */
    +package org.apache.rocketmq.client.producer.selector;
    +
    +import org.apache.rocketmq.client.producer.MessageQueueSelector;
    +import org.apache.rocketmq.common.consistenthash.ConsistentHashRouter;
    +import org.apache.rocketmq.common.consistenthash.Node;
    +import org.apache.rocketmq.common.message.Message;
    +import org.apache.rocketmq.common.message.MessageQueue;
    +
    +import java.util.ArrayList;
    +import java.util.List;
    +
    +public class SelectMessageQueueByConsistentHash implements MessageQueueSelector {
    +
    +    private final ConsistentHashRouter<MQNode> consistentHashRouter = new ConsistentHashRouter<MQNode>(null, 0);
    +    private volatile List<MessageQueue> lastMqs = new ArrayList<MessageQueue>();
    +    private final int virtualNodeNum;
    +
    +    public SelectMessageQueueByConsistentHash() {
    +        this.virtualNodeNum = 10;
    +    }
    +
    +    public SelectMessageQueueByConsistentHash(int virtualNodeNum) {
    +        this.virtualNodeNum = virtualNodeNum;
    +    }
    +
    +    @Override
    +    public MessageQueue select(List<MessageQueue> mqs, Message msg, Object arg) {
    +        if (arg == null) {
    +            throw new NullPointerException();
    +        }
    +        synchronized (consistentHashRouter) {
    +            rehash(mqs);
    +            return consistentHashRouter.routeNode(arg.toString()).mq;
    +        }
    +    }
    +
    +    private void rehash(List<MessageQueue> mqs) {
    --- End diff --
    
    How about do a check before allocating two array lists?
    Check if mqs is the same as lastMqs.
    For in production environment, the mqs is rarely changed.


> Provide a handy message queue producer for order message sharding
> -----------------------------------------------------------------
>
>                 Key: ROCKETMQ-136
>                 URL: https://issues.apache.org/jira/browse/ROCKETMQ-136
>             Project: Apache RocketMQ
>          Issue Type: Improvement
>          Components: rocketmq-client
>    Affects Versions: 4.1.0-incubating
>            Reporter: Jaskey Lam
>            Assignee: Jaskey Lam
>            Priority: Minor
>             Fix For: 4.2.0-incubating
>
>
> When order message is needed, users need to provide a message queue selector to make sure that the messages which has the same shading key should be sent to the same message queue.
> Actually this is a very common scenario with a common solutions, say consistent hashing.
> We should provide a handy selector for them to easily do that, what they only need to provide is a sharding key.
> A consistent hash selector will meet most of the user's need.



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