Re: Database Kernels and O_DIRECT

Andrew Dunstan wrote:

>
> 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