minimize filesystem caching effects:
The nocache tool tries to minimize the effect an application has on the Linux file system cache. This is done by intercepting the open and close system calls and calling posix_fadvise() with the POSIX_FADV_DONTNEED parameter. Because the library remembers which pages (ie., 4K-blocks of the file) were already in file system cache when the file was opened, these will not be marked as “don’t need”, because other applications might need that, although they are not actively used (think: hot standby).
4 cases were more serious the second time around