MUF abends because of a SC22 in DBIOSPR

Products

• Datacom
• Datacom/DB

Issue/Introduction

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 to not allow the I/Os to exceed 480, keeping a cushion or pad of 20 I/O requests. Once 480 is reached, no new I/Os are issued until the number drops below 480.

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.

Environment

Release: Datacom/DB

Resolution

Decrease the number of IOTASKS or use SMPTASKS to evenly farm out or distribute the work on multiple CPUs.