how to run sap transaction st02 and do performance analysis in sap memory

How to run SAP transaction ST02 and do performance analysis in SAPmemory/buffer area

SAP transaction ST02 can be used to view SAP Buffer and memory configuration for a SAP instance and review SAPmemory quotas for individual user job or process as well as current SAP buffer status, SAP memory utilization at SAPinstance or user/transaction level. This post would cover following areas:

1. How to run SAP memory usage monitor and navigate through important ST02 screens.

2. How to understand SAP ST02 screens: main/summary screen or SAP memory Quota screens etc.

3. How to use SAP ST02 to do SAP memory and buffer performance analysis.

1. How to run SAP Memory/Buffer monitor and navigate through important screens of the monitor

1.1 How to start SAP Buffer/Memory monitor

To start SAP Buffer/Memory monitor, you can either use menu path or run sap transaction ST02 directly. This would showbuffer/memory configuration and usage for the instance where the SAP ST02 is started. After you execute SAP transactionST02, SAP buffer and memory overview/status screen would show up:

Figure 1 ST02 memory overview/summary

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You can refresh the screen to show new status, Except Curr. Use and MaxUse, all other non-configuration data areaccumulated data since last startup of the SAP instance in question.

1.2 How to navigate through important screens of the SAP ST02 transaction.

Following screen shows menu path and hot key which you can use to access other SAP st02 screens:

In following sections, I would mention some important screens which I use most often.

1.2.1 How to review SAP Buffer and Memory for another instance of the SAP system

If your system has more than one instance, you can display to another instance via following path from figure-1 screen:Environment -> RFC server or press shift+F4 key until a popup window shows up with a list of instance, you can click the oneyou would like to review.

1.2.2 How to navigate to SAP quotas screen SAP memory allocation for a single work process

SAP ST02 Quota screen shows type of memory and amount allowed for a single SAP work process as well as memoryallocation sequence. There are two sequences one is for dialog type tasks like online transaction executed by a SAP user,the other is for non-dialog tasks like SAP SM37 jobs.

You can get the memory quota screen for single sap work process via menu Goto->SAP memory-> Quotas:

Figure 2 ST02 memory quotas for a work process



1.2.3 How to navigate to mode list screen showing memory usage at user/transaction level

You can bring up mode list screen from main screen (Figure 1) via following path: Details analysis menu -> SAP Memory ->Mode list

Figure 3 Memory usage by SAP users

1.2.4 How to navigate to SAP memory history screen

SAP ST02 provide you history memory usage information. You can access this information via following menu path or hotkeys from the memory initial screen.

Following is a part of history screen :

Figure 4 ST02 History data

If you are just interested in buffer history for one buffer type, you can double click the corresponding row in Figure-1 screen the screen would change, on the new screen click on History Icon, SAP ST02 would bring up history screen just for theselected buffer type.

History information can reveal abnormal memory usage as well as high-water mark namely Maximum Usage since the datewhen instance is started or restarted. SWAP difference between two dates can show the growth pattern base on that, youcan see whether action is needed to correct the situation.



1.2.5 How to navigate to parameter screen

You can check SAP memory/buffer parameters via Icon or following the menu path: Goto-> Profile Parameters -> Current.

Following is a part of SAP memory/buffer parameter screen:

You can select a profile parameter and change it. But the change would only come into effect after the instance is bounced.SAP has a tool to allow you to change SAP memory parameters(Extended Memory and Heap memory) dynamically thismeans that your change would become effect immediately.

2. Explanation on SAP ST02 screens

Here I would choose several frequent referred ST02 screens and give more information to help you understand the datapresented by SAP ST02 transaction.

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 infollowing sections.

2.1.1 Buffer section explanation

Column field explanation

Screen Field ExplanationBuffer 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.

Column ExplanationSap Memory Show type of SAP memoryCurr. Use % = allocated memory/total-memory X 100% for the type of memory in questionCurrUS[KB] Currently used memory at the instanceMaxUse[KB] High-water mark since the SAP instance is startedIn Mem[KB] Configured total memoryOnDisk[KB] Configured disc space(Virtual memory),only eligible for Page memory and roll memory.SAPCurCache SAP Cursor CacheHitRatio Applicable for ID and statement Caches.

2.2 SAP Memory Quotas screen

Column Explanationtexts Sap tasks type like dialog, background etc

Step Sequence allocation next step only if memory from previous step can not meet memory requirement for thetask/workprocessMemorytype 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

3.1 SAP Buffer analysis

SAP Buffer analysis is to focus on following items

Hit rate: should not be lower than 98% except program buffer, single record buffer and export/import bufferwhere low hit rate is normally considered acceptable.

Swaps: The goal is to avoid swap in all Buffer except program buffer. Low swaps in single record buffer andexport/import buffer is not significant.

Enough Free memory and free directory entry: this would help avoid swap. If there is free space but there isno free directory, this would cause swap. Vice Versa.

If you saw big swaps, less free directory and/or less free memory space, it would reduce swap to increase configured memoryspace and/or max directory entry when free main memory is available.

SWAP and buffer invalidation is different concept. Buffer invalidation is due to changes on buffered object which would involvetransfer from database table. SWAP is due to shortage of free buffer space/directory. Buffer invalidation is not reflected inswap column but it would increase database access. SWAP itself would not increase database access. But next read on aswap buffered object would trigger systems action to reload the swapped object from database, this would increasedatabase access.

If database access is high for table space buffer area, you might need to review table buffering for the instance, this could bedue to a frequent changed buffered table whose buffering should be turned off. You can use SAP transaction ST10 to reviewtable buffering or you can navigate to table buffering from the main screen.

3.2 SAP Memory analysis

3.2.1 SAP memory analysis at instance level

SAP Extended memory, Heap memory, Roll memory and Page memory are SAP memory space shared by all SAP workprocesses. SAP memory analysis is to focus on following items

Free memory: We should have enough free memory in Extended and Heap memory. Current used memoryshould not exceed 80% to ensure that free memory is still available for new memory demand.

Maximum memory: Maximum used memory since start of instance should be lower than 80% of whatconfigured memory for Extended memory and Heap memory. Otherwise, there might be memory contentioncausing job/program cancellation. For SAP page memory and Roll memory, the maximum used memoryshould not exceed the amount configured in Memory column.

It is important to online transaction performance to have enough extended memory. If this is no free extended memory, SAPwork process would get memory from heap area based on SAP allocation sequence for dialog tasks. Once a Dialog is usingheap memory, the SAP dialog process would be in a Private mode cannot be shared with other tasks. If many dialogprocesses are put into private mode, this would impact dialog response time and RFC task due to shortage of shared dialogwork processes.

If current usage is high for extended memory/heap memory space, you can go to mode list screen (Figure 3 screen) to findwhich program and users are consuming those memory. Base on those information, you can decide whether we need to tunememory usage for the programs and jobs, reschedule the jobs/programs or we need to have more extended memory.

3.2.2 SAP memory analysis at individual job/user level

Figure 2 screen also shows type and amount of memory which can be used by a single SAP work process and which oneshould be used first (Allocation sequence). The actual memory allocation for a SAP work process would depend on memorydemand of the program and availability of memory of each type. A SAP work process would be terminated by SAP system ifthere is no memory at last step of allocation. Based on figure 2, Dialog task can have up to 7M memory in the extendedmemory space, if an online SAP process needs less than 7M bytes memory and there is at least 7M bytes free memory fromExtended Memory, it would not use Roll and heap memory. If the online process needs more memory than what isavailable in heap memory after it consumes available memory from extended and roll memory space, the program/processwould be terminated by system due to memory resource contention issue. In similar way, a SAP background job/processwould be terminated by SAP system if the job needs more memory than what is available at extended memory space due tothe fact that the job needs more than what allowed by the quota or running out of extended memory.



4. Further clarification

SAP ST02 memory monitor is one of SAP resource monitoring tools together with SAP operating system monitor (ST06) ,SAP database monitor (DB02 or ST04) and SAP work process monitor (SM50/SM66). In my view, if there are free CPUpower, free memory and enough free sap work processes, then a well-tuned SAP system should be healthy from SAP systemperformance point view. Based on SAP buffer and memory monitoring, the outcome of review can be one or several actions:increase SAP memory allocation at instance level, adjust memory quotas for individual process, tune application job/programand/or rescheduling job/program. How many memory can be configured is limited by physical memory and configured swapspace for the server.



how to run sap transaction st02 and do performance analysis in sap memory

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