MPE/iX 5.5 Operating System Limits

Recovery
4 ~48000 Copy forward user transactions per log XM Checkpoint Mechanism
5 255 System Logs XM Logfile/Volset
Restrictions
(1) XM locks
When a XM transaction is started a control block lock is done on the XM protected
object. Currently the number of XM cb_locks per transaction is limited to 10.
(2) Open files during recovery
At the recovery time, the maximum number of files that can be opened is set to 4096.
(3) Open transactions during recovery
The maximum number of transactions that can be open at any one point during recovery
is 4096.
(4) XM checkpoint mechanism
A transaction is considered to be long if it spans two checkpoints (how long it takes
depends on how fast the log fills up). If we do not do something about long transactions,
we will run out of log file space. Because of recycling of log space may overwrite log
records for a long running transaction. It will cause system abort 2200 for system log. For
user log, the solution is to "copy forward" log records of the long running transactions at
wrap log time.