Anatomy of a Write Operation

Let’s learn how GFS handles a write operation.

What is a chunk lease?

To safeguard against concurrent writes at two different replicas of a chunk, GFS makes use of chunk lease. When a mutation (i.e., a write, append or delete operation) is requested for a chunk, the master finds the ChunkServers which hold that chunk and grants a chunk lease (for 60 seconds) to one of them. The server with the lease is called the primary and is responsible for providing a serial order for all the currently pending concurrent mutations to that chunk