Question

在mongo db命令中sh.startBalancer（超时，间隔）根据文件： timeout整数等待的毫秒数。 interval integer每个等待休眠周期的毫秒数。有人可以详细解释参数含义。运行sh.startBalancer（）时默认值是什么？

Answer 1

sh.startBalancer（超时，间隔）将做两件事：

更新config.settings {_id：'balancer'}文档，以允许平衡器运行。
检查每个“间隔”毫秒是否已获取分布式锁定，表明平衡器正在运行。它将执行此操作，直到指定'timeout'毫秒为止，此时此方法将断言。

即使您达到超时，config.settings更新仍会在启用平衡器的情况下保持不变。

如果您对查看代码感兴趣，可以在没有括号和参数的情况下运行sh.startBalancer，对它调用的函数执行相同的操作。以下是MongoDB 3.2.6：

> sh.startBalancer
function (timeout, interval) {
    sh.setBalancerState(true);
    sh.waitForBalancer(true, timeout, interval);
}

> sh.setBalancerState
function (onOrNot) {
    sh._getConfigDB().settings.update(
    {_id: "balancer"}, {$set: {stopped: onOrNot ? false : true}}, true);
}

> sh.waitForBalancer
function (onOrNot, timeout, interval) {

    // If we're waiting for the balancer to turn on or switch state or
    // go to a particular state
    if (onOrNot) {
        // Just wait for the balancer lock to change, can't ensure we'll ever see it
        // actually locked
        sh.waitForDLock("balancer", undefined, timeout, interval);
    } else {
        // Otherwise we need to wait until we're sure balancing stops
        sh.waitForBalancerOff(timeout, interval);
    }

}

> sh.waitForDLock
function (lockId, onOrNot, timeout, interval) {
    // Wait for balancer to be on or off
    // Can also wait for particular balancer state
    var state = onOrNot;
    var configDB = sh._getConfigDB();

    var beginTS = undefined;
    if (state == undefined) {
        var currLock = configDB.locks.findOne({_id: lockId});
        if (currLock != null)
            beginTS = currLock.ts;
    }

    var lockStateOk = function() {
        var lock = configDB.locks.findOne({_id: lockId});

        if (state == false)
            return !lock || lock.state == 0;
        if (state == true)
            return lock && lock.state == 2;
        if (state == undefined)
            return (beginTS == undefined && lock) ||
                (beginTS != undefined && (!lock || lock.ts + "" != beginTS + ""));
        else
            return lock && lock.state == state;
    };

    assert.soon(
        lockStateOk,
        "Waited too long for lock " + lockId + " to " +
            (state == true ? "lock" : (state == false ? "unlock" : "change to state " + state)),
        timeout,
        interval);
}

sh.startBalancer（超时，间隔）参数的含义？

1 个答案: