Datacom dynamic extend risks or failures

Products

• Datacom
• Datacom/AD
• Datacom/DB

Issue/Introduction

We had previously opened a case asking for some information about Datacom area space, and in that case you gave us article 9503, titled "How to extend a Datacom area while the database is open". We did a test in our LAB environment, and it worked ok. Now we are going to try it in our development environment, which is more critical in case of failure.

The question is, if for some reason, the dynamic extend fails, what can be the consequences for Datacom? Would the Datacom MUF still continue to work if the dynamic extend fails? Or is there any risk of other malfunctions or abends if this process fails?

Environment

z/OS

Resolution

The article you mentioned will help you to do a "directed dynamic extend" where you can specify the amount you want for the new extent, and it runs as soon as you issue the command. This is different than the normal dynamic extend, which runs when the current extent reaches 100% full, and uses the pre-defined secondary allocation or the CXX-based Dynamic Extend amount.

The potential for failure is the same in either case. If you have an area (a physical dataset) that is at the limit for its extents (for example, you have reached 16 extents on a single volume), a dynamic extend will fail–whether it is a normal extend, or a directed extend. Along with that, if your regular processing fills the last extent available for the file, you will not be able to extend, and your file will cause a B37 abend.

In any case, the MUF will continue processing, but your application will not be able to add any more records until you fix the out-of-space problem.

The best way to handle this (assuming you are running Version 15.1 or later) is to use a function called Online Area Move (OAM), where you would allocate a new file at the desired larger size, initialize it for Datacom processing, and then start a process in the MUF to move all the data into the new file. This all happens while the database is open for processing, and like the dynamic extend, is unseen by the end-user.

Therefore, as I look at a database to determine what to do, I think of a couple different things:

1. If the file is less than 10 or 12 extents, and the volume where the file is placed has sufficient free space, I would issue a Directed Dynamic Extend for a large extent to be added so I do not have to consider this again for a while.
2. If I have used most of the possible extents, or if I am not sure there is freespace on the volume to get what I need, I will create a new file and use the OAM processing to ensure my application will continue to run.

Both of these manual options and processes can be done before there is a problem, and if successful, will help you to avoid a problem and an outage because of an out-of-space condition.

Additional Information

For more information on the Online Area Move process, please refer to the Datacom Core documentation, in the Online Area Move section.

As always, please contact Broadcom support for Datacom if you have further questions.