Checkpoint not complete

The "checkpoint not complete" messages are generated because the logs are switching so fast that the checkpoint associated with the log switch isn't complete. During that time, Oracle's LGWR process has filled up the other redo log groups and is now waiting for the first checkpoint to successfully execute. It can't overwrite the contents of the redo log until the information covered by that log is flushed to the data files. Oracle will stop processing until the checkpoint completes successfully.

Performance can be improved by increasing the log sizes so that logs switches occur at the recommended interval of 15 to 30 minutes. Identify the current size of the redo log members from V$LOG, record the number of log switches per hour and increase the size of the log to allow Oracle to switch at the recommended rate of one switch per 15 to 30 minutes.
For example, if the database log size is 1 megabyte and you are switching logs every 1 minute, you will need to increase the log size to 30 megabytes in size to allow it to switch every 30 minutes.

The problem is that many applications have workloads that vary throughout each 24-hour time-period. In addition, application-processing workloads may vary according to the days of the calendar month. Month-end and mid-month processing may increase the number of changes occurring in the database. This higher level of activity may cause the redo logs to be filled much more quickly than during off-peak times. The DBA must make sure that the on-line redo logs don't switch too often during periods of high activity and switch often enough during times of low processing workloads. In addition, administrators must also be concerned about how the size of the online redo logs affect instance recovery. The less checkpoints taken, the longer instance recovery will take.