Explain Transaction Transparency ?

Which allows a transaction to update data at more than one network: the basic concepts are :

Remote requests Remote Transactions Distributed Transaction Distributed requests

A remote request is a single SQL statement access the data that are to be processed by a single remote data base processor.

A remote transaction composed of several request, access data at a single remote site.

A distributed request : Let a single SQL statement reference data located at several different local ( or) remote DP sites.

A distributed transaction composed of several distribution requests access data at different sites.

Two phase commit protocol : Two –phase commit protocol requires DO–UNDO–REDO protocol.

DO performs the operations & records the “before “ & after values in the transaction log.

UNDO reverses on operation.

REDO redoes on operation. Two phase commit protocol is implemented in two phases.

Phase 1 : preparation :

coordinators sends a prepare to commit message to all subordinates.

subordinates receive the message & send acknowledgement.

It all nodes are prepared to commit the transaction goes to phased or it aborts the transaction.

Phase 2 : Final commit :

1.The coordinates board costs a commit message to all subordinates & waits for the replies.

2. Each subordinate receive the commit message & then update the database using the DO protocol.

3. The subordinate reply with a committed (or) not committed message to the coordinates.

4. If one (or) more subordinates didn’t commit, the coordinator sends an short message three by for them to UNDO as changes.