Today we start discussing ZooKeeper which is a wait free coordination for Internet scale systems. It allows distributed processes to co-ordinate with each other through a shared hierarchical namespace of data registers. We can think of it as a distributed lock server but it involves much more. It is available as open-source and introduces simple interface involving naming, configuration management,  lock and synchronization and group services. This can be customized. It is used in configuration management in an unattended manner or for simpler deployment or provisioning. It is also used for distributed cluster management. It can be used for distributed synchronization in the form of locks, barriers and queues. We recall that the gossip protocol was used to propagate the updates via message exchanges.  The Zookeper service is replicated over a set of machines. All machines store a copy of the data (in memory). A leader is elected on service startup. Clients only connect to a single zookeeper server and maintains a TCP connection. Clients can only read from any Zookeeper server, writes go through the leader and need majority consensus. The data model consists of a hierarchical namespace where each node in the namespace is called a ZNode. ZNode paths are canonical, absolute and slash-separted and they have no relative references.
#coding exercises
Find the product of first K magic numbers
int GetMagicN(int n)
{
int power = 1;
int result = 0;
while (n)
{
power = power * 5;
if  ( n & 1)
    result += power;
n >> = 1;
}
return result;
}
long GetMagicProduct (int k)
{
 long result = 0;
 for (int I = 1; I <= k; I++)
      result *= GetMagicN(k);
return result;
}
It might be interesting to note that since the magic numbers map to bit representations of consecutive integers, we can easily tell how far apart are perfect powers of 5 in the magic number sequence.