In true 24*7 production environments there is an increasing expectation that simple(on the face of it) DDL changes should be able to break-in concurrent with application workload. In the case of high-arrival rate transactions even at the quietest times contention can occur with the execution, for example, of a DDL ALTER TABLE to set DATA CAPTURE CHANGES where a deadlock is detected with active dependent packages. This is particularly problematic the larger the number of active dependent packages involved. This typically results in the DDL ALTER being selected as the victim of the deadlock with SQLCODE-904 RC00E7000F TYPE801 returned the batch job executing the DDL.
We have DDLTOX ZPARM set to the default value of 1.
Increasing this is not relevant in the case of a deadlock.
However it would be useful if DB2 had a user controlled option to favor the DDL in the case of a deadlock such that it is not selected as the victim of the deadlock.
This would have the benefit of permitting the DDL to continue and successfully break-in without having to agree /take a planned service outage for the relevant applications.
Note. This idea does NOT make the existing idea DB24ZOS-I-1082 redundant, they address separate ends of the spectrum regarding DDL behaviour.
|Who would benefit from this IDEA?||Customers in high volume 24*7 environments experiencing difficulties in implementing some DDL changes concurrent with application workload|
|Priority Justification||The reputation of DB2 is being tarnished due to the inability to implement a simple DDL ALTERs without scheduling an outage|
How should it work?
Possibly using DDLTOX ZPARM to provide an installation an option to indicate to DB2 they want DDL to be favored in the case of a deadlock.
As a suggestion using the current highest permitted value(i.e. 254) to indicate to DB2 to favor DDL in case of a deadlock . In this case we would suggest 254 should result in DDLTOX of 1 (the default for timeout multiplier) plus a change in behaviour in case of deadlock as detailed above.
An alternative would be a new ZPARM, however if IBM would prefer to use an existing ZPARM then the above is offered as proposal.
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