There is a tool you can use:
https://jforum.dev.java.net/source/browse/jforum/tools/searchIndexer/
It's a command line tool, that reads your database and indexes it.
As of JForum 2.1.8, we are supporting Lucene, which will be much better than the current search implementation.
Rafael
[originally posted on jforum.net by Rafael Steil]