Chad, thank you for complete explanation of available options. As to you questions:

1. We have a TASKMGR task which calculates the size of each global in all databases. It's usually scheduled by our customers for daily run.
2. The main purpose of collecting such info is the ability to quickly answer the questions like this: "why my database is growing so fast?". Integrity Check is not used for the similar purpose because it can't be scheduled for daily run due to its relative slowness in our versions of Cache and IRIS.

Hiroshi, take it easy - everybody can make a mistake.
Meanwhile, I'm sure that $ZIO was initially intendent for terminal devices only. Here is the oldest link I was able to find: https://cedocs.intersystems.com/documentation/cache/cache41/olr/olrvzio....
Why not use ##CLASS(%SYS.ProcessQuery) for similar purposes? It's more powerful and better documented than some "mystic" system variables and functions.
Happy writing!

Hiroshi,
May I ask you where did it ever work?

Here are the results of quick test in Studio Output window: 

w "*"_$zio_"*"
**
w "*"_$zutil(67,12,$j)_"*"
*MYPC*
w ##CLASS(%SYS.ProcessQuery).Open("P"_$j).ClientNodeName ; prefered (documented) way
MYPC
w ##CLASS(%SYS.ProcessQuery).Open("P"_$j).ClientIPAddress
10.8.3.37

Alternative program which supports CacheActiveX connection showed the same results, by the way, regardless of server's platformwhether it was UNIX/Linux or Windows.

IRIS for Windows (x86-64) 2021.1 (Build 215U) Wed Jun 9 2021 09:39:22 EDT

while results were similar in all previous Cache/IRIS versions I managed to run.

Standard queues provide at-least-once delivery, which means that each message is delivered at least once. FIFO queues provide exactly-once processing, which means that each message is delivered once and remains available until a consumer processes it and deletes it. Duplicates are not introduced into the queue.

..so I guess that you mean standard queue with several worker processes dequeuing items from the queue. In this case the CPU utilization would likely depend on the number of workers, wouldn't it?