As I explained in another reply, PostgreSQL does no write directly to the files/file cache. It has its own buffer cache and only calculates the checksum when fl

As I explained in another reply, PostgreSQL does no write directly to the files/file cache. It has its own buffer cache and only calculates the checksum when flushing dirty pages to disk (where PostgreSQL does a normal, cached write syscall and then fsyncs). The lack of O_DIRECT causes other performance issues, but not this one.