MPE/iX 5.5 Operating System Limits

two types of objects that have variable access rights, (NM program files and NM library
files), it is very unlikely that this limit can be reached.
This table also limits the maximum number of extents for open non-resident objects with
variable access rights to 64520. It is unlikely that this maximum number could be
obtained since it would imply that each object has a multiple of eight extents and the tree
is completely balanced and full. This number was obtained by multiplying the maximum
number of entries (8065) by the maximum number of extents per entry (8).
NOTE: Objects with fixed access rights are defined as those for which ALL pages have
identical read and/or write access as well as the same privilege level. Extent information
about objects with fixed access rights is kept in the Extent B-tree (KSO 55). All but two
types of objects have fixed access rights. However, NM program files and NM library
files have variable access rights. Page 0 has write access in addition to the read/execute
access that is given to the other pages of the file. Extent information about objects with
variable access rights is kept in the Extent AR B-Tree (KSO 57).
(3) VSOD GUFD table - KSO201
Every object in the system requires an entry in either the VSOD or VSOD GUFD table
(with the exception of certain resident objects that reside in the Disabled Expandable
VSOD table, kso #255). All file objects obtain an entry in the VSOD GUFD table when
they are mapped in (or opened). When the file is mapped out, the entry is linked onto a
list known as the 'LRU' (or Least Recently Used) list. If the same file is opened again, the
LRU list is searched to see if an entry already exists for that file. If so, we re-use the entry
and save the overhead of mapping the file in again. If the entry is not on the LRU list, a
new entry must be obtained. If there are no free entries in the table, an entry is obtained
from the LRU list. The object previously associated with that LRU list is now considered
to be mapped out.
This table limits the number of open file objects to 91180. Each entry in the VSOD
GUFD table will have a pointer to one node in the Extent B-tree or Extent AR B-tree
table. As discussed in the Extent B-tree documentation, one or more nodes of the B-tree
may be used for any given object, depending on the number of extents that have been
allocated for it.
(4) VSOD + VSOD GUFD tables