客戶端控制檯一直報一下異常：
redis.clients.jedis.exceptions.JedisDataException: READONLY You can't write against a read only slave.
從字面意思理解的話，意思是寫到了只讀的從節點。正常情況下是不會出現這個問題的。只會發生在master已經切換，但是client使用的master沒有刷新的情況。
可以看下jedis的源碼(2.9版本)：
protected class MasterListener extends Thread {
省略一些代碼...
@Override
public void run() {
running.set(true);
while (running.get()) {
j = new Jedis(host, port);
try {
// double check that it is not being shutdown
if (!running.get()) {
break;
}
j.subscribe(new JedisPubSub() {
@Override
public void onMessage(String channel, String message) {
log.fine("Sentinel " + host + ":" + port + " published: " + message + ".");
String[] switchMasterMsg = message.split(" ");
if (switchMasterMsg.length > 3) {
if (masterName.equals(switchMasterMsg[0])) {
//正常來說發生master切換，client會收到switchmaster消息，從而重新初始化連接池。 initPool(toHostAndPort(Arrays.asList(switchMasterMsg[3], switchMasterMsg[4])));
} else {
log.fine("Ignoring message on +switch-master for master name "
+ switchMasterMsg[0] + ", our master name is " + masterName);
}
} else {
log.severe("Invalid message received on Sentinel " + host + ":" + port
+ " on channel +switch-master: " + message);
}
}
}, "+switch-master");
} catch (JedisConnectionException e) {
if (running.get()) {
log.log(Level.SEVERE, "Lost connection to Sentinel at " + host + ":" + port
+ ". Sleeping 5000ms and retrying.", e);
try {
Thread.sleep(subscribeRetryWaitTimeMillis);
} catch (InterruptedException e1) {
log.log(Level.SEVERE, "Sleep interrupted: ", e1);
}
} else {
log.fine("Unsubscribing from Sentinel at " + host + ":" + port);
}
} finally {
j.close();
}
}
}
伴隨着往slave節點寫的錯誤還可以看到：
log.log(Level.SEVERE, "Lost connection to Sentinel at " + host + ":" + port
+ ". Sleeping 5000ms and retrying.", e);
這個錯誤日誌，說明曾經客戶端丟失了連接。
查看jedis github相關isuse，果真有相關內容。可以參考：
https://github.com/xetorthio/jedis/pull/1566
https://github.com/xetorthio/jedis/issues/1953
這個問題在2.9.3版本已經得到正確修復：
@Override
public void run() {
running.set(true);
while (running.get()) {
j = new Jedis(host, port);
try {
// double check that it is not being shutdown
if (!running.get()) {
break;
}
/* 這裏就是關鍵，只要while循環一次則重新初始化一次。正常情況是會阻塞在 j.subscribe 所以不會一直執行。
* Added code for active refresh
*/
List<String> masterAddr = j.sentinelGetMasterAddrByName(masterName);
if (masterAddr == null || masterAddr.size() != 2) {
log.warning("Can not get master addr, master name: "+ masterName+". Sentinel: "+host+"："+port+".");
}else{
initPool(toHostAndPort(masterAddr));
}
//正常情況下會阻塞在這裏
j.subscribe(new JedisPubSub() {
@Override
public void onMessage(String channel, String message) {
log.fine("Sentinel " + host + ":" + port + " published: " + message + ".");
String[] switchMasterMsg = message.split(" ");
if (switchMasterMsg.length > 3) {
if (masterName.equals(switchMasterMsg[0])) {
initPool(toHostAndPort(Arrays.asList(switchMasterMsg[3], switchMasterMsg[4])));
} else {
log.fine("Ignoring message on +switch-master for master name "
+ switchMasterMsg[0] + ", our master name is " + masterName);
}
} else {
log.severe("Invalid message received on Sentinel " + host + ":" + port
+ " on channel +switch-master: " + message);
}
}
}, "+switch-master");
} catch (JedisException e) {
if (running.get()) {
log.log(Level.SEVERE, "Lost connection to Sentinel at " + host + ":" + port
+ ". Sleeping 5000ms and retrying.", e);
try {
Thread.sleep(subscribeRetryWaitTimeMillis);
} catch (InterruptedException e1) {
log.log(Level.SEVERE, "Sleep interrupted: ", e1);
}
} else {
log.fine("Unsubscribing from Sentinel at " + host + ":" + port);
}
} finally {
j.close();
}
}
}