Insert statement deletes older table records

Hi,

 

When I execute an insert statement, older table records are deleted even though my insert statement works. It always keeps the maximum number of records in the table to 4200 records. So If I added 3 more records, it deletes the first three records in the table even though it adds the 3 new records.

 

Based on my research it appears postgreql has no limit to number of records in a table - what should I do to avoid this behavior.

 

Thanks.