Hi Gayathri,
If you read the note which i mentioned above the audit log is saved in memory and after some time if the memory is full then last message gets deleted from the cache.
For example 1000 audit log messages are saved in memory then file message is 900th message and mail message is 1010th message then the mail message audit log will be deleted because there is a space for last 1000 messages in the cache.
Regards,
Praveen.