Long-term trending and avaialbility reports for large implem

Hi All,
We have a 2.9 Nagios implementation with about 3000 host and 9000 service checks. The built-in trend and availability reports work well for time periods of about a week. However longer time period trend reports can be pretty slow due to the number and size of the log files Nagios needs to parse.

In this situation, what kind of alternatives have you used to generate monthly or annual availability and trend reports?