MongoDB维护

Question

我正在为MongoDB编写一个维护脚本,它将按计划从副本集中压缩集合.到目前为止,我所拥有的脚本看起来很好,正在完成预期对主节点和辅助节点执行的工作.但是有一个问题:

使用MongoDB副本集的系统是一个高可用性Web队列,它不断被写入和读取.因此,即使调用rs.StepDown()几秒钟的停机时间也是绝对不可接受的.有没有办法安全地降级数百个客户端没有MongoExceptions的主节点？

谢谢!

ps这里是脚本的实际版本,应该在每月一次的低负载时间通过cron-job运行

// assuming we are a replica set ;-)
if(rs.isMaster().setName){
    try {
        //check if the script is run against a master
        if(rs.isMaster().ismaster){ //if so, step down as master        
            print("Connected to a PRIMARY node")
            print("Will try to step down as primary");
            rs.stepDown();

            // after stepdown connections are dropped. do an operation to cause reconnect:
            rs.isMaster();            

            // now ready to go.      
            // wait for another node to become primary -- it may need data from us for the last 
            // small sliver of time, and if we are already compacting it cannot get it while the 
            // compaction is running.            
            var counter = 1;
            while( 1 ) { 
                var m = rs.isMaster();
                if( m.ismaster ) {
                    print("ERROR: no one took over during our stepDown duration. we are primary again!");
                    assert(false);
                }

                if( m.primary ){ // someone else is, great
                    print("new master host is: "+m.primary);
                    break; 
                }
                print("waiting "+counter+" seconds");
                sleep(1000);
                counter++;
            }
        }else{
            print("Connected to a SECONDARY node");
            print("Going into Recovery Mode and Compacting");            
        }

        // someone else is primary, so we are ready to proceed with a compaction
        print(" ");
        print("Compacting...");
        print("- queue");
        printjson( db.runCommand({compact:"queue"}) );
        print(" ");

    } catch(e) { 
        print(" ");
        print("ACHTUNG! Exception:" + e);
        print(" ");
    }
}else{
    print('This script works with replica sets only');
}

Answer 1

有没有办法安全地降级数百个客户端没有MongoExceptions的主节点？

不.MongoDB没有任何形式的"预期转换"或"维护转换".

做这个压缩循环是正确的做法.但您必须等待维护窗口来压缩主要维护.

...是一个高可用性的Web队列.

你是否使用Capped Collections？加盖的集合不需要压缩.无法调整封顶集合中的对象的大小,但这通常不是Queue对象的问题.

虽然不是理想的解决方案,但可以解决您的问题.