MUF abends because of a SC22 in DBIOSPR

Document ID : KB000049480
Last Modified Date : 14/02/2018
Show Technical Document Details

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.