Oracle RAC SCN propagation mode (BROADCAST-ON-COMMIT)

The SCN propagation mode of BOC is only propagated when the SCN of a node changes, and the LGWR process works in conjunction with the LMS process to synchronize the SCN,LGWR between nodes to write redo information to the Redo log file and send the latest SCN. The LMS process is responsible for the propagation of SCN information between nodes.

There are two kinds of SCN transmission modes in BOC: Indirect and direct way

The indirect approach takes 8 steps:

Step 1: The user process commits the transaction and notifies the LGWR process, then enters the wait state, and the corresponding wait event is log file sync.

The step 2:LGWR process sends the commit SCN for the transaction to a local LMS process.

The step 3:LGWR process writes the re-information for the transaction to the Redo log file.

Step 4: The local node of the LMS process will contain the SCN information sent to all remote nodes of the LMS process.

Step 5: The LMS process for all remote nodes receives the SCN information and feeds the LMS process back to the local node.

Step 6: Re-message the I/O request is complete and feedback to the LGWR process.

Step 7: The local node's LMS process notifies LGWR that all remote nodes have received the SCN for the transaction.

Step 8: The LGWR process of the local node notifies the user that the process transaction submission is complete.

Steps 2 and 3 are simultaneous, with the aim of improving the efficiency of the SCN's propagation

The sequence of steps 5 and 6 may be reversed, depending on the I/O performance of the disk on which the cluster private network and redo log files reside

Direct mode takes 7 steps

Step 1: The user process commits the transaction and notifies the LGWR process, then enters the wait state, and the corresponding wait event is log file sync.

Step 2:LGWR process directly sends the information that contains the transaction submission SCN to all remote nodes of the LMS process

The step 3:LGWR process writes the re-information for the transaction to the Redo log file.

Step 4: The LMS process for all remote nodes receives the SCN information and feeds the LMS process back to the local node

Step 5: Re-message the I/O request is complete and feedback to the LGWR process.

Step 6: The local node's LMS process notifies LGWR that all remote nodes have received the SCN for the transaction.

Step 7: The LGWR process of the local node notifies the user that the process transaction submission is complete.

The direct way is one step less than the indirect method, which is determined by the LGWR according to the system load, which SCN is used to propagate.

Oracle RAC SCN propagation mode (BROADCAST-ON-COMMIT)