As I was monitoring the database, saw the 'sql area' usage rising up to 123MB and 'free memory' was 10MB. Then all of a sudden during the fag end of the day, 'free memory' is 116MB and 'sql area' is 14MB.

What causes this to happen? AFAIK, no one gave a 'flush shared_pool'. So, provided no one did that, what other issues cause this to happen?