APT_IO_MAP/APT_IO_NOMAP and APT_BUFFERIO_MAP/APT_BUFFERIO_NOMAP

In many cases memory mapped I/O contributes to improved performance. In certain situations, however, such as a remote disk mounted via NFS, memory mapped I/O might cause significant performance problems. Setting the environment variables APT_IO_NOMAP and APT_BUFFERIO_NOMAP true turns off this feature and sometimes affects performance.

AIX® and HP-UX default to NOMAP. Setting APT_IO_MAP and APT_BUFFERIO_MAP true can be used to turn memory mapped I/O on for these platforms.