DISTRIBUTED SYSTEM

DISTRIBUTED SYSTEM NOTE,IOE,TU,BCA

GLOBAL STATE AND STATE RECORDING

In a distributed system, the global state comprises the local states of each process, which include messages sent and received, as well as the state of each communication channel. The challenge lies in capturing this global state accurately. The primary difficulty arises from the absence of a global clock, resulting in the local states being recorded at different times for each process.

“Global State is the set of all local state of all process plus local state of all communication channels.”

Global Snapshot = Global State Individual state of each process in the distributed system + Individual state of each communication channel in the distributed system 

• Capture the instantaneous state of each process 

• Capture the instantaneous state of each communication channel, i.e., messages in transit on the channels

TYPES OF GLOBAL STATE

1. CONSISTENT GLOBAL STATE- if local state of any process says that it has received a message then there should be any such process whose local state says that it has send a message or the message should be present in the communication channel.

 

2. INCONSISTENT GLOBAL STATE -message has been sent but it is neither in local state of any process nor in communication channel
3. TRANSITLESS GLOBAL STATE-A “transitless” global state is one where each message that has been  sent ,has been received.none of the message is in communication channel or in other words the local state of all communication channel is empty.
4. STRONGLY CONSISTENT GLOBAL STATE-all global state that is both consistent and transitless