2. Explanation on SAP ST02 screens
2.1. SAP Buffer and Memory overview/summary screen
ST02 overview screen show information at instance level and has several sections:
- Top shows instance name, instance startup date and snap-shot of date time.
- Buffer section shows different SAP buffer configuration and current status.
- SAP Memory section shows SAP memory configuration and current status.
- Call Statistics shows database access information.
I have not encountered a performance case which I need “Call Statistics” data to do analysis, It looks like straightforward. From performance point view, buffer sections and SAP memory section is more critical – that is what I am going to cover in following sections.
2.1.1. SAP Buffer section explanation
Column field explanation
|Buffer||Type of buffer like nametab, Program etc.|
|Hitratio %||Namely buffer quality =( total access – physical access)/ total access x 100%.|
|Alloc. KB||Configured or allocated memory space for the buffer type in question.|
|Freesp. KB||Free space = allocated memory space – occupied memory space.|
|Dir. Size||Maximum number of buffer object that can be kept in the related buffer.|
|FreeDirEnt||Free Directory Entry = Directory Size – used Dir Entry.|
|% Free Dir||= free Directory / Dir. Size X 100%.|
|Swap||Number of buffered objects which has been swapped to page area.|
|DB Access||Number of data transfers from the data base to the related buffer.|
2.1.2. SAP Memory section explanation
This section shows configured memory/virtual memory for a list of sap memory type and their memory usage.
|Sap Memory||Show type of SAP memory|
|Curr. Use %||= allocated memory/total-memory X 100% for the type of memory in question|
|CurrUS[KB]||Currently used memory at the instance|
|MaxUse[KB]||High-water mark since the SAP instance is started|
|In Mem[KB]||Configured total memory|
|OnDisk[KB]||Configured disc space(Virtual memory),only eligible for Page memory and roll memory.|
|SAPCurCache||SAP Cursor Cache|
|HitRatio||Applicable for ID and statement Caches.|
2.2. SAP Memory Quotas screen
|texts||Sap tasks type like dialog, background etc.|
|Step||Sequence allocation – next memory area only if memory allocated in previous steps is not enough.|
|Memory type||3 possible memory types under current SAP design: Roll, Extended and Heap|
|Amount||Configured the memory size for the tasks.|
The SAP screen quotas screen (see figure 2) answers the question of what is maximum memory a SAP process can use:
- Dialog tasks can use memory up to an amount <=Roll + Extended + Roll + Heap. Transaction executed online by SAP user is a dialog tasks.
- Non-dialog tasks can use memory up to an amount <=Roll + Heap + Extended. SM37 background job is a non-dialog task.
Dialog tasks are executed in SAP Dialog work process. RFC calls and online transactions are executed in dialog work processes. Job, update and spool are non-dialog tasks. Jobs are executed “BGD” SAP work processes. Update tasks are executed in SAP “UPD” work processes. SAP transaction SM50/SM66 is a work process monitor.
2.3 SAP mode list screen
Figure 3 screen shows SAP Memory usage for every external session by every logon user who is in the instance.
|user||Sap user –same user might have more than one entries|
|EM used||Extended Memory used by a user session in KB|
|Heap||Heap memory used by a user session in KB|
|Other columns like “I-mode G1″ etc||I have not found the need to use those columns for SAP memory analysis.|
Mode list has two sections – the upper section show current status, the lower section shows history information.