In the intended use case, the lack of kernel-level caching can be a performance win. A database can do a better job of caching than the kernel can because it ha

In the intended use case, the lack of kernel-level caching can be a performance win. A database can do a better job of caching than the kernel can because it has a clearer picture of the expected access patterns. O_DIRECT in this kind of application makes a lot of sense.