I have wondered (somewhat fruitlessly) for several years about the possibilities of special purpose lightweight file systems that could relax some of the assumptions and checks used in general purpose file systems. Such a thing might provide most of the benefits of a "database kernel" without imposing anything extra on the database application layer.
CPU is usually cheap compared to disk io.
There are two things that might be worth looking into:
Oracle released their cluster filesystem (ocfs) as a GPL driver for Linux. It might be interesting to check how it performs if used for postgres, but I fear that it implicitely assumes that the bulk of the caching is performed by the database in user space.
And using O_DIRECT for the WAL logs - the logs are never read.
-- Manfred
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