MPE/iX 5.5 Operating System Limits

The new native mode Writer ID Table (KSO227), contains a maximum of 16,384 entries.
Each concurrent writer of a message file requires one entry. As a result a maximum of
16384 processes can concurrently open an IPC file with write access.
(2) Fs gdpd table - KSO222
Every file that is opened gets a Global Data Pointer Descriptor (GDPD) entry. Most
GDPD entries are allocated within the Process Local File Descriptor (PLFD) table. Each
PLFD entry is paired with a GDPD entry within the PLFD table. However, if a native
mode file is opened with Multi Access (intra-job) or G-Multi Access (inter-job), then the
GDPD entry is allocated from the System GDPD table. Subsequent opens of the same
Multi Access file will share the same GDPD entry. If the file is a CM type file (eg.
Message file, RIO, Circular, or Device file), then the GDPD entry is allocated in the
PLFD, and the FMAVT table (DST 44) manages the Multi Access.
The GDPD table limits the number of unique NM files that can be opened simultaneously
with Multi Access or G-Multi Access to 16,384.
(3) Plfd - kpo017
There used to be a Process Local File Descriptor (PLFD) table allocated for each process.
Every file that is opened gets a PLFD entry. (For those of you familiar with, MPE VE,
this is analogous to an AFT entry). In MPE iX 4.0 in order to save SR6/SR7 space, the
Process Local File Descriptor was modified to allocate files in 64 file chunks. The KPO
#17 in the PIBX will still point to the PLFD, but it will now point to a PLFD index. The
PLFD index is a data structure that poinDIVto the plfdare 64es. The index value for a
filenum will be the file number div 64 (there is 64 files per PLFD).
The maximum number of files that can be opened simultaneously by each process has
been set to 1024.
(4) NM ipc table
The FSIPC Object (KSO225) is used as an internal data structure for message files (IPC)
to pass data between processes. Within this data structure, one or more port entries are
allocated for processes that open message files and to send WAIT or REPLY messages
under EOF conditions. As a result, two processes accessing a single message file may use
anywhere from 5 to 7 FSIPC entries in the FSIPC object.