sentinel.md

Every time Redis is doing failover, it calls sentinelStartFailover(). Sentinels exchange hello messages using Pub/Sub and updates last_pub_time variable. So, let's dig more into this. Here is the snippet (Systemtap) I used to probe user-space:

probe process("/usr/local/bin/redis-server").function("sentinelStartFailover")
{
        elapsed = gettimeofday_ms() - $master->last_pub_time
        printf("%d.%03ds\n",
                (elapsed / 1000), (elapsed % 1000));
}

Manual failover using redis-cli

127.0.0.1:16380> sentinel failover sentinel_de
OK

Another console:

[root@redis-node1 ~]# stap sentinel.stp
0.835s

/etc/init.d/redis-de stop

[root@redis-node1 ~]# /etc/init.d/redis-de stop
Stopping ...
Redis stopped

Another console:

[root@redis-node1 ~]# stap sentinel.stp
5.843s