1. I found a cookie problem recently, basically the cookie can not be set from a web app on a linux server. It turned out the server had a very off time. And the cookie expiration time is calculated by current server time + cookie life time. If the server is behind the time too much, it will no set the cookie to the browser any more.
2. Always use varchar instead of char in DB column design to save space if the column's String length is unknown. In DB2 use varchar type directly, in Oracle we should use varchar2 type since varchar is reserved for other purpose according to one article.