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Tuesday, May 28, 2019

SAP ABAP Kernel SNAPSHOTS

If you haven’t already seen it, quite some time ago I wrote a brief blog post on the Flight Recorder for the NW AS Java stack.
Many years later, I’ve still very rarely seen a company use the flight recorder information.
Snapshots (also known as SAP Kernel Snapshot) in the NW AS ABAP stack are much the same thing.

When a serious condition occurs within the ABAP stack, a system message is registered in the system log (SM21) and a snapshot of the current system status is generated.
An example condition could be that a work process has died without warning, or that there was a lack of resources (background or dialog), hard shutdown of the SAP system/server or that the dispatcher queue was full.

Each of these scenarios is logged under system log message code “Q41”, in category “DP” and “Process No” “000”.
The only difference between the failures is the text following “reason: “ which is passed in by the calling Kernel function.


Q41 in system log

According to the SAP notes, the initial feature was provided in 2013 as per SAP note: 1786182 “CreateSnapshot: Collecting developer traces using sapcontrol”.
It was provided as an additional set of web service functions on the SAP instance agent (sapstartsrv) and is therefore accessible from outside of the SAP system if need be.

Originally, it appears to have been designed to be operated independently outside the SAP system, however SAP note 2640476 – “How to analyze Server Snapshot with kernel snapshot analyser” from 2019, indicates that it was integrated into the SAP Kernel in 7.40 (i.e. that the Kernel itself can instigate the snapshot).

How can we use SNAPSHOTS?

You can either access the snapshot zip files directly on the O/S level using O/S commands to extract and inspect the files, or you can use the ABAP transaction code SNAPSHOTS to see an ALV list of snapshot files.

In the O/S the files are stored in /sapmnt/<SID>/global/sapcontrol/snapshots.

Usually, the sequence of access is dictated by an extraordinary event within the ABAP stack, then you may see the System log entry which will inform you of the existence of a snapshot, but you may choose to regularly check in SNAPSHOTS anyway as part of your daily checks.

SNAPSHOTS (program: RS_DOWNLOAD_SNAPSHOTS)




As you can see the ABAP transaction incorporates the reason for the snapshot, whereas the O/S file listing is not so easy to identify.
If you want to use the O/S level, then unzipping the file will reveal a file called “description.txt” which states the reason for the snapshot:



From the SNAPSHOTS transaction (program RS_DOWNLOAD_SNAPSHOTS) you have the option to download the snapshot file to your front-end.
Here you can unzip the file and expose the contents.

Once you have extracted the snapshot zip file, you will see a tree structure under which will sit a number of XML files:



The names of the XML files are fairly self explanatory.
ABAPGetWPTable for example, is the name of the sapcontrol web service function that is used to get the ABAP Work Process Table (same as transaction SM50).

Opening any of the XML files is going to be a lot easier with Microsoft Excel.
Except the XML is not suitable for Excel without a little bit of manipulation (this is a real pain, but once in Excel you will love it).

Edit the XML file in a text editor and delete the header lines that are the result of the web service function call, leaving just the raw XML:



Save the file and then it will happily open in Excel!








As mentioned, this is a snapshot of the work process table at the point when an issue occurred.
Very useful indeed.
You have lots of other XML files to examine.

Plus, as an added bonus, further down the directory structure of the snapshot zip file, is a complete XML snapshot of all the developer trace files for this app server:




How can we manually create SNAPSHOTS?

You can manually create and administer the snapshots (they will need clearing down) using the SAP instance agent (sapcontrol) web service commands as follows:
sapcontrol -nr <##> -function [snapshot_function]
  CreateSnapshot [<description> [<datcol_param> [<analyse_severity -1..2>
  [<analyse_maxentries> [<analyse_starttime YYYY MM DD HH:MM:SS>
  <analyse_endtime YYYY MM DD HH:MM:SS> [<maxentries>
  [<filename1> ... <filenameN>]]]]]]]
  ReadSnapshot <filename> [<local filename>]
  ListSnapshots
  DeleteSnapshots <filename1> [<filename2>... <filenameN>]
The ABAP transaction SNAPSHOTS only allows you to view/download and delete the snapshots. You can not trigger them using any standard transaction that I can find.