The redo log buffer is an area of memory within the SGA that holds information about changes to the database, called redo log entries . These entries are used if database recovery is necessary, and they contain information required to reconstruct changes made by INSERT, UPDATE, DELETE, CREATE, DROP, or ALTER statements.

The redo log buffer is circular—that is, when it is full, entries are written to it from the beginning. As discussed earlier, the LGWR process writes the contents of the redo log buffer to the active redo log file on disk. The size of the redo log buffer is determined by the INIT.ORA parameter LOG_BUFFER, which is expressed in bytes. The default value of this size is four times the DB_BLOCK_SIZE, but it is often desirable to set this value higher, particularly if there are many or long transactions generating high rates of redo generation.