Two latches control access to the redo buffer. The redo allocation latch must be acquired in order to allocate space within the buffer. If the redo log entry to be made is greater than the configuration parameter LOG_SMALL_ENTRY_MAX_SIZE, the session that acquires the redo allocation latch can copy the entry into the redo buffer immediately while holding the allocation latch.
If the log entry is greater than LOG_SMALL_ENTRY_MAX_SIZE, the session releases the redo allocation latch and acquires the redo copy latch in order to copy the entry.
There is only one redo allocation latch, but there may be up to LOG_SIMULTANEOUS_COPIES allocation latches.
Note: The LOG_SMALL_ENTRY_MAX_SIZE and LOG_SIMULTANEOUS_COPIES parameters were made obsolete in Oracle 8.1.