The following fragment of a message appeared on the Firebird development list. As the question and answer are interesting, I thought I would put it on the blog.
"If I want to make cache flushes to disk very rare, do I set MaxUnflushedWrites & MaxUnflushedWriteTime to -1 or to some large value?
What other settings adjustments can make table flushes to disk more rare?
Is there any combination of settings that will keep the entire db in cache and never flush it to disk?"
Dimitry Yemanov answered as follows:
Forced writes = OFF (at the database level)
MaxUnflushedWrites = -1,
MaxUnflushedWriteTime = -1 (in firebird.conf)
With these settings, Firebird will never explicitly flush the cache to disk. However, flushes may still be performed by the operating system in the background. I believe you understand that these settings are somewhat risky from the database consistency point of view. There is no way to completely avoid flushes at all.