A new Check in EarlyWatch Alert: DDLOG Sequence Exhaustion may cause unplanned Downtime
There may be a new check in the EarlyWatch Alert report that asks for your attention, and you may have questions:
- What is it about?
- I do not see the check in my report! Why?
- Should I be worried?
- What happens if the sequence reaches its limit and what shall I do then?
- How do I stop the alert? I have already planned the necessary action!
If you have further questions, then please send a ticket on the component SV-SCS-EWA and mention the check’s name in the subject, send me an e-mail, or drop a comment under this post.
But now up to the questions:
1. What is it about?
The check uses the current level of the DDLOG Sequence. That sequence is a crucial figure deep down in the technical basis of the SAP system. It is used to synchronize certain buffers between different application servers. It used to be implemented as a signed 32-Bit integer which limits the range of possible values. It ranges from −231 to +231−1 which is approximately a bit more than ±2 billion.
While the figure does not grow extremely fast, it may reach the limit unnoticed.
By the way, there are means to slow down the growth of DDLOG Sequence numbers.
2. I do not see the check in my report! Why?
There are several reasons possible:
- It is essential that we get the figures from your system in the first place. You must allow and activate Online Collectors. Please read SAP Note 2827332 how to do this.
- Your system uses a database system different than SAP HANA, Oracle, or MaxDB.
The DDLOG mechanism is implemented differently depending on the primary database system. The subject discussed here is only relevant for systems on those three database systems mentioned above.
- Your system runs on a kernel of release 781 or above.
There, the number range has been expanded to a 64-Bit integer. Thus, the limit is only theoretical. The time until an unlimited system license expires on December, 31st, 9999 would be a much shorter than that.
- The estimated time until the DDLOG sequence runs out on numbers is longer than two years and we will not alert you too early.
3. Should I be worried?
The short answer is No.
The long answer is: It depends.
If you have a system that you run without interruption 24 hours a day, 7 days a week and all year long, then any downtime may be an unwelcome event. In that case you should look out for a possible maintenance window. As written in the following answer, a downtime is needed to get over the limit.
If you have already planned your maintenance windows, then the estimated date when the limit will be reached will help you to determine a convenient time for the necessary action.
In general, the issue that the DDLOG sequence is running out of numbers is quite a rare event, alas not impossible. So, it might take a while until you see this check in your report.
4. What happens if the sequence reaches its limit and what shall I do then?
When the limit is reached then programs end unexpectedly, and you experience ABAP dumps with SQL Errors that point to a database object with DDLOG in its name.
If you happen to fall into this pit, then the only way out is a stop of all application servers and manual action on database level. Otherwise, just do it at your convenience during the next planned maintenance window. SAP Note 1312102 tells you what to do.
(Remark: The note is planned to be revised and to include the actions for MaxDB.)
5. How do I stop the alert? I have already planned the necessary action!
Yes, we feel you. Getting the same red alert every week, even if you have already planned the necessary actions is nagging.
Like mentioned above, it may happen that you never see this check in the EarlyWatch report of your system. But after you have read this far into this blog post, you are prepared.