Have you checked to see if the system that ends up winning the ENQ is
the same as the one which was running the job that just ended and did
the DEQ? It seems to me that the DEQing system has the best chance of
winning any race condition since it is the first to know of the DEQ
and thus the first to be able to grab the ENQ lock.
At 14:46 -0600 on 01/17/2013, Peter Hunkeler wrote about Tasks
ENQ'ing exclusive on resource not getting control in :
<x-charset UTF-8>It was my understanding that tasks enqueueing on a
resource are getting control in FIFO order, if contention existed.
Today, we had a situation where this was not true.
Environment is as follows:
- 4 system parallel sysplex, z/OS V1.13, GRS STAR mode.
- a dozen or so jobs running the same program are active across all
4 systems at a time. More job being submitted as jobs end (more or
less).
- the programs are serializing using EXCLUSIVE ENQ on a resource,
scope systems
As expected, one job is running, all others are waiting to get the
resource assigned.
But suddenly, we the recognized that jobs on two systems never got
running. They have been waiting for the resource for hours, while
newer jobs got control one after the other. So resource assignment
is clearly not FIFO. We then saw (in EJES) that once a job ended,
all waiting jobs are active for a very short time, then one job
continues to run while all other are waiting again.
I have RTFM, and still think ENQ is FIFO. I have not found anything
related to GRS STAR mode that contradicts.
I have not followed GRS new lately. What am I missing?
--
Peter Hunkeler
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