[otrs] more than 6000 closed tickets

Hi there, Here's a question for the ones with large implementations of OTRS. One of the environments I take care of have reached the 6000 closed tickets. Unfortunately OTRS won't show them all -only the 6000 newest. I was doing my homework and the research only led me to the following user's manual entry http://doc.otrs.org/2.4/en/html/c2632.html in which they talk about performance but they won't mention anything about not showing old tickets after the 6000 limit is reached. Has anyone faced this same situation? Any help is much appreciated! Greetings, Leonardo Certuche