The full replication algorithm is an extension of the read replication algorithm. It allows multiple nodes to have both read and write access to shared data blocks ( the multiple readers-multiple writers protocol ). Because many nodes can write shared data concurrently, the access to shared data must be controlled to maintain its consistency.

One possible way to keep the replicated data consistent is to globally sequence the write operations. A simple strategy based on sequencing uses a single global gap-free sequencer which is a process executing on a host participating in DSM. When a process attempts a write to shared memory, the intended modification is sent to the sequencer. This sequencer assigns the next sequence number to the modification with this sequence number to all sites. Each site processes broadcast write operations in sequence number order. When a modification arrives at a site, the sequence number is verified as the next expected one. If a gap in the sequence numbers is detected, either a modification was missed or a modification was received out of order, in which case a retransmission of the modification message is requested. In effect, this strategy implements a negative acknowledgment protocol.

                  
DSM Home   Subway   Algorithms  Read Repl    
  Page       Map                Algorithm