Use the SET PLAN option in the ISQL tool to test queries and see their performance and what the optimizer chooses as the query plan. Avoid this syntax, or if you must use it, specify your own query plan. Tune InterBase's Cache InterBase maintains its own cache in the server's RAM of database pages currently in use. The default cache size in V4.0 is 75 database pages. For a database with 1Kb database pages, this is still only 256Kb.
Most servers have a lot of memory.
Try tuning the cache up from its default of 256 database pages to as many as 10,000 database pages. At some point, you will find diminishing returns, but some experimentation will reveal that point. This technique also avoid unnecessary network traffic. The OS will decide to write the contents of the cache to the physical hard disk periodically. For example, use disk mirroring to maintain a duplicate copy of the data.