The redo log buffer is a RAM area that works to save changes to data, in case something fails and Oracle has to put it back into its original state.The redo log buffer changes made to the records are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files, they will first brought to redo log buffers in SGA and LGWR will write into files frequently. LOG_BUFFER parameter will decide the size.