For the redo log buffer, if your database is experiencing a high degree of waits for space in the log buffer, consider increasing the size, but remember that it is almost never necessary for the size of a redo log buffer to exceed several hundred kilobytes.
For the buffer cache, make use of the buffer cache sizing advice embodied in
the V$DB_CACHE_ADVICE data dictionary table, either via your own queries or
the Enterprise Manager interface to this information. Each row in this view
shows the estimated I/O activity for a given cache size; you can thus see
how much more (or less) disk reads would be required for various cache
This was first published in May 2004