Description:
Datacom MUF address space fails due to a SC22 abend in DBIOSPR module. This means that the address space has exceeded the threshold of outstanding I/O requests allowed by the operating system.
IBM does not allow more than 500 concurrent I/Os per address space at any given point in time.
Datacom/DB code ensures that any point in time we will not allow the I/Os to exceed 480, meaning we would keep a cushion or pad of 20 I/O requests. Once we reach 480, we stop new I/Os to be issued until the 480 number subsides below it.
The number of times this limit has been reached during a MUF execution is reported at MUF EOJ:
X_IO_OS_THRESHOLD
The count of times Datacom/DB constrained and started no I/O because the outstanding I/O was 480 or more.
However a high number of IOTASKS may cause all the IO subtasks to be issuing simultaneously and this limit is possible to be violated.
Solution:
Decrease the number of IOTASKS or use SMPTASKS to evenly farm out or distribute the work on multiple CPUs.
Release:
Component: DB