public void dropPartialFileFromCache(FileDescriptor fd, long offset, long len, boolean sync) {
        if (sync) {
            try {
                fd.sync();
            } catch (SyncFailedException e) {
                logger.warning("Sync failed while dropping cache: " + e.getMessage());
            }
        }
        if (valid()) {
            PosixFAdvise.posix_fadvise(fdField.getNativeFD(fd), offset, len, PosixFAdvise.POSIX_FADV_DONTNEED);
        }
    }
Will hint the OS that data read so far will not be accessed again and should hence be dropped from the buffer cache.
@param fd The file descriptor to drop from buffer cache.
vespajlib/src/main/java/com/yahoo/io/NativeIO.java