Memory Management in 7.4_ Kernel

5/21/2018 Memory Management in 7.4_ Kernel

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Memory Management simplifications in ABAPKernel 7.4*


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Memory Management simplifications in ABAP Kernel 7.4*

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TABLE OF CONTENTS

OVERVIEW ....................................................................................................................................................... 3

NEW PARAMETER FORMULAS ..................................................................................................................... 3

TROUBLESHOOTING ...................................................................................................................................... 4

512 GB LIMIT .................................................................................................................................................... 5

CONCLUSION ................................................................................................................................................... 5


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OVERVIEW

This paper describes Memory Management parameterization changes in 7.4* kernel. The main goal of these

changes was simplification: the administrator will be enabled by setting only one profile parameterPHYS_MEMSIZE to automatically initiate changes of dependent parameters. This is a fast way to scale theABAP instance memory consumption. Within the context of this development the old fashioned Zero AdminMM for Linux and Windows

- was extended to all other operating systemsand

- reimplementedvia formula based parameters

More information about the Zero Administration in previous releases can be found in:http://help.sap.com/saphelp_erp60_sp/helpdata/en/3c/05863c6800924fe10000000a114084/content.htmhttp://help.sap.com/saphelp_erp60_sp/helpdata/en/84/7ed384d81f11d188be0000e83539c3/content.htm

NEW PARAMETER FORMULAS

The formulas may depend on kernel release and operating system. You can get a list of parameters withformula based defaultvalues e.g. with help of sappfparexecutable. Below is an example for kernel 7.41PL22 on Linux:

Formulas support in the profiles is implemented as of kernel 7.40, described in:http://help.sap.com/saphelp_nw74/helpdata/en/a7/d631e255594dc19899706a3a7c3fe8/content.htm?frameset=/en/51/319798cc7a428a896af0bc2a00adc7/frameset.htm

> sappfpar all | grep "SAP: ("abap/buffersize = (ceil($(em/initial_size_MB)*1024*0.15/4096) * 4096)abap/heap_area_total = (max($(PHYS_MEMSIZE)*1024*1024 * 0.1, $(abap/heap_area_dia) * 2 ))

abap/programs = ($(abap/buffersize)/4)abap/shared_objects_size_MB = (min(20000, $(em/initial_size_MB)*0.02))em/blocksize_KB = (ceil($(em/initial_size_MB) * 1024 / 100000 / 4096) * 4096)em/global_area_MB = (min($(em/initial_size_MB) * 0.05, 32000))em/initial_size_MB = (min(512000, $(PHYS_MEMSIZE) * 0.7))em/max_size_MB = ($(em/initial_size_MB))rdisp/PG_SHM = (max(min(1000+40*max(5,floor(($(PHYS_MEMSIZE)-128)*25/128)),16384),1024))rdisp/max_websocket_connections = ( $(rdisp/tm_max_no) / 2 )rdisp/wp_ca_blk_no = ($(rdisp/elem_per_queue)*3)rsdb/ntab/entrycount = ($(zcsa/db_max_buftab))rsdb/ntab/ftabsize = (min(500000, ($(rsdb/ntab/entrycount))))rsdb/ntab/irbdsize = ($(rsdb/ntab/ftabsize) * 0.2)rsdb/ntab/sntabsize = ($(rsdb/ntab/ftabsize) * 0.1)rsdb/obj/buffersize = (max(4096,$(PHYS_MEMSIZE)*1024 * 0.01))rsdb/obj/max_objects = (max(2000,$(rsdb/obj/buffersize) / 4))rsts/ccc/cache07 = ($(rsts/ccc/cachesize) * 0.1)

rtbb/buffer_length = ($(zcsa/table_buffer_area) * 0.1 / 1024)rtbb/max_tables = ($(zcsa/db_max_buftab) * 0.1)zcsa/db_max_buftab = (max(20000,$(zcsa/table_buffer_area) / (5 * 1024) ))zcsa/table_buffer_area = (min(3333333333, (max(30000000,($(em/initial_size_MB) * 1024 * 1024 * 0.1)))))ES/SHM_MAX_SHARED_SEGS = ( ($(em/global_area_MB) + $(abap/shared_objects_size_MB) + $(rtbb/buffer_length)/1024 +

$(zcsa/table_buffer_area)/1024/1024 ) / $(ES/SHM_SEG_SIZE) + 1 )


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sappfparcan also be used for checking your profile:

In the example above the parameter abap/buffersizethat has been set to a fix value although its defaultvalue is a formula, was found.

TROUBLESHOOTING

In this section we would like to analyze a real lifeexample from an administratorspoint of view.A system consisting of 2 ABAP instances is installed on a host with 64GB main memory. Every instance isrunning with PHYS_MEMSIZE=30% setting in profile. Customers experience sporadic memory lack issues

- Rabaxes- EmAlloc failed errors in dev trace- Extended Memory Dump in dev trace

Examples for memory lack Rabaxes are: TSV_TNEW_PAGE_ALLOC, LOAD_NO_ROLL,STRING_LENGTH_TOO_LARGE, TSV_TNEW_BLOCKS_NO_ROLL_MEMORY

The administrator is analyzing Extended Memory Dumps in dev traces, they appear as shown below:

The administrator cant identify any particular user which is using too much memory. This means that theserver has been overloaded sporadically, i.e. at peak times when many users are working simultaneously.

>sappfpar pf= check_formula

***WARNING: formula parameter: abap/buffersize = 350000 found in profileErrors detected..................: 0Warnings detected................: 1

...

...Extended Memory Dump

Act. USER SUM IM0 IM1_________________________________________________________________

SAP_SMDMON(T52_U5144_M0) [ 0.9] > 0.8< ------0990FUSRABCD(T461_U4228_M0) [ 23.8] > 23.6< ------USER_TEST_12(T461_U4228_M0) [ 23.8] > 23.6< ------

...

...# CHAIN OWNER STATE

0 0 ***free*** free1 1 EG_GLOBAL_AREA shared...2537 1 EG_GLOBAL_AREA shared2538 2538 SAP_SMDMON(T6_U377_M0) detached2539 2539 K8NZDJEQHUR(T558_U15419_M0) detached

...


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Proposed solution: set PHYS_MEMSIZE=45% in the profile to allow every instance to use64GB * 0.45 = 28,8GB

main memory. This will automatically increase the value of dependent parameters, e.g:

PHYS_MEMSIZE=30% PHYS_MEMSIZE=45%

em/initial_size_MB 13653 (MB) 20480 (MB)abap/heap_area_total 20452265165 (Byte) 30678397747 (Byte)

Keep in mind that the instance has to be restarted for activating its new values!

PHYS_MEMSIZE can be also set to absolute values instead of percentage:PHYS_MEMSIZE=40000

which would mean Megabytes in the Example above.

512 GB LIMIT FOR ALL OPERATING SYSTEMS

PHYS_MEMSIZE is not a hard limit for an ABAP instance. This is a guide value to make the instanceaware about the amount of main memory it should use. This limit can be overrunned in heavy loadscenarios.

Kernel 7.4* has been tested up to PHYS_MEMSIZE=512000 settings. It is not recommended to run asingular ABAP instance with more than 512000 MB.

Warnings in dev traces would give you a hint if you are trying to run an instance with more than thatmemory size, e.g.:

* WARNING=>DpCheckParams: invalid value for PHYS_MEMSIZE=600000 [dpInit.c]

* WARNING=>DpCheckParams: check message: Parameter value out of range (16...512000) [dpInit.c]

It is recommended to use default memory management models on every OS:es/implementation = std (Unix)es/implementation = view (Windows)ES/TABLE = UNIX_STD (Unix)ES/TABLE = SHM_SEGS (AIX only)

The memory management parameter formulas have been optimized for the memory model cases above.

The only platform has been optimized not for default case only is OS/400 which has been tuned for bothUNIX_STD and SHM_SEGS memory models.

CONCLUSION

Formula based parameters introduced in 7.4* and supported for all operating systems offer a new simplifiedway of administration for ABAP instances in an SAP system. They will be used in ABAP server memorymanagement already.

About the author: Gennady Maly is working at SAP development since 2001.


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Memory Management in 7.4_ Kernel