Oracle maintains tables used for internal processing. When Oracle needs to make a change to these tables, it internally generates a SQL statement. These internal SQL statements generate recursive calls. This statistic increments each time redo entries are copied into the redo log buffer. The active log file has filed up and Oracle is waiting for disk space to be allocated for the redo log entries.
Space is created by performing a log switch.
Small Log files in relation to the size of the SGA or the commit rate of the workload can cause problems. When the log switch occurs, Oracle must ensure that all committed dirty buffers are written to disk before switching to a new log file. If you have a large SGA full of dirty buffers and small redo log files, a log switch must wait for DBWR to write dirty buffers to disk before continuing. Normally, redo that is generated and copied into the log buffer need not be flushed out to disk immediately. The log buffer is a circular buffer that LGWR periodically flushes.