Two latches control access to the redo buffer. The Redo Allocation latch must be acquired in order to allocate space within the buffer. Once space is allocated, the session releases the Redo Allocation latch and acquires the Redo Copy latch in order to copy the entry.
Contention for these latches is rare in modern versions of Oracle. Contention for the Redo Allocation latch may indicate that the log buffer should be increased in size, or that redo buffer pressure be reduced, perhaps by considering NOLOGGING operations.
Oracle automatically allocates the number of copy latches based on the number of CPUs available on your system. If you experience waits for the redo copy latch, you may consider increasing the value of the undocumented parameter _log_simultaneous_copies.
Note: Oracle Corporation recommends changing undocumented parameters ONLY at the direction of Oracle Support.