log file switch (archiving needed)
Waiting for a log switch because the log that the LGWR will be switching into has not been archived yet. Check the alert file to make sure that archiving has not stopped due to a failed archive write. To speed archiving, consider adding more archive processes or putting the archive files on striped disks.
log file switch (checkpoint incomplete)
Waiting for a log switch because the session cannot wrap into the next log. Wrapping cannot be performed because the checkpoint for that log has not completed.
log file switch (clearing log file)
Waiting for a log switch because the log is being cleared due to a CLEAR LOGFILE command or implicit clear logfile executed by recovery.
log file switch (private strand flush incomplete)
User sessions trying to generate redo, wait on this event when LGWR waits for DBWR to complete flushing redo from IMU buffers into the log buffer; when DBWR is complete LGWR can then finish writing the current log, and then switch log files.