HBase客户端访问超时的多个因素及参数

在一个需要低延时响应的hbase集群中，使用hbase默认的客户端超时配置简直就是灾难。

但是我们可以考虑在客户端上加上如下几个参数，去改变这种状况:

1. hbase.rpc.timeout: RPC timeout, The default 60s, 可以修改为5000(5s)

2. ipc.socket.timeout: Socket link timeout, should be less than or equal to RPC timeout, the default is 20s

3. hbase.client.retries.number: The number of retries, default is 14, 可以配置为1

4. hbase.client.pause: Sleep time again, the default is 1s, can be reduced, such as 100ms(在1.1版本的hbase已经变为100ms,请对照你使用的hbase版本)

5. zookeeper.recovery.retry: The number of retries ZK, Can be adjusted to 3 times, ZK is not easy to hang, And if HBase cluster problem, Each retry retry the operation of ZK will be, The total number of retry ZK is: hbase.client.retries.number * zookeeper.recovery.retry, And sleep time each retry will have exponential growth of 2, Every time you access the HBase will try again, In a HBase operation if it involves multiple ZK access, If ZK is not available, There will be many times the ZK retry, Is a waste of time.

6. zookeeper.recovery.retry.intervalmill: Sleep time ZK retries, the default is 1s, can be reduced, for example: 200ms

7. hbase.regionserver.lease.period: A scan query when interacting with server timeout, the default is 60s.(在1.1版本，该参数名为hbase.client.scanner.timeout.period)

Retry interval strategy RPC:

public static long getPauseTime(final long pause, final int tries) {

int ntries = tries;

// RETRY_BACKOFF[] = { 1, 1, 1, 2, 2, 4, 4, 8, 16, 32, 64 }

    if (ntries >= HConstants.RETRY_BACKOFF.length) {

      ntries = HConstants.RETRY_BACKOFF.length - 1;

    }

    long normalPause = pause * HConstants.RETRY_BACKOFF[ntries];

    long jitter =  (long)(normalPause * RANDOM.nextFloat() * 0.01f); // 1% possible jitter

    return normalPause + jitter;

  }

Retry interval strategy ZK:

// RetryCounter类

//Sleep time 指数级增长

public void sleepUntilNextRetry() throws InterruptedException {

    int attempts = getAttemptTimes();

    long sleepTime = (long) (retryIntervalMillis * Math.pow(2, attempts));

    timeUnit.sleep(sleepTime);

       }

// retriesRemaining, The default value ismaxReties, Each retry after reduction1

       public int getAttemptTimes() {

          return maxRetries-retriesRemaining+1;

       }