It was discovered that a nightly backup process which issues 17 DCMT QUIESCE SEGMENT segname ID xxxx HOLD commands, only executes the first 11 commands.
The last 6 are ignored. The IDMS LOG shows the DC260100 Log echo for all 17 but only 11 are executed.
Client has a startup proc that sets the runtime MAX TASK value to a very low number (15 more than the number of system tasks - thus only 15 additional tasks can be active at any time).
When the Database Resource Controller module gets the commands it attempts to #ATTACH HELOT tasks for each command.
If the #ATTACH fails due to being at the runtime MAX TASKS, it will retry once and if it still fails the command is cancelled because allowing it to wait could cause unwanted results as the Quiesce could finally engage at a point when the process is considered complete.
Client increased the runtime MAX TASKS value so that all of the DCMT QUIESCE commands could execute.
* NOTE: As of March 30 2021 SE is developing a PTF that will produce a message under such circumstances to indicate that the command was cancelled, as a delay due to MAX TASKS could cause unwanted results.