SAP Basis Tech Supports

Symptom
This note provides information regarding uncertainties when you use the SAP Web Dispatcher.
Other terms
sapwebdisp, HTTP load balancing, webdispatcher, wbdisp, wdisp, dispatcher,
HTTP, HTTPS.
Reason and Prerequisites
You want to use the SAP Web Dispatcher for HTTP(S) load balancing.
Solution
Version-independent comments
As of Release 6.40, the SAP Web Dispatcher is delivered on the kernel CD for the SAP Web Application Server.
The Web Dispatcher Release 6. 40 is available on SAP Service Marketplace:
http://service.sap.com/patches under:
“Additional Components” -> “SAP Kernel” -> “SAP KERNEL 32/64 BIT” -> “SAP KERNEL 6.40 32/64 BIT” -> <Operating System> -> “Database Independent”, package dw_<patch no>_xxxx.SAR
http://service.sap.com/patches under “Entry by Application Group” -> “SAP NetWeaver” -> “SAP NETWEAVER” -> “SAP NETWEAVER 04″ -> “Entry by Component” -> “AS ABAP” -> “SAP KERNEL (32/64Bit, Unicode/non Unicode)” -> <OS platform> -> “Database Independent”, Package dw_<patch no>_xxxx.SAR
For Web Dispatcher 7.00, a specific SAR sapwebdisp_< PL >-<…>.SAR is available on SAP Service Marketplace. For more information, see Note 908097.
The current version of the SAP Web Dispatcher is Version 7.10. This is available on SAP Service Marketplace at http://service.sap.com/patches:
Support Packages and Patches
-> Entry by Application Group
-> Additional Components
-> SAP Kernel
-> SAP Kernel 32 Bit or SAP Kernel 64 Bit
-> SAP Kernel 7.10 nn Bit
-> Operating system platform
-> “Database independent
The package is called sapwebdisp_< PL >-<…>.SAR. < PL > indicates the patch level.
The SAP Web Dispatcher is downward-compatible, which means that the SAP Web Dispatcher release may be higher or the same as the release of the back end system. The patch level may be different to the patch level of the back end system. This is valid for ABAP and J2EE backend systems as of Basis/Kernel 6.20. If you use Basis 6.10, you must refer to Note 499327. We recommend that you use SAP Web Dispatcher 7.10 for SAP NetWeaver2004 and for SAP NetWeaver2004S back-end systems (Version 6.xx) if this dispatcher is compatible with your operating system. If this dispatcher is incompatible with your operating system, you must use SAP Web Dispatcher 6.40.The SAP Web Dispatcher is independent of the patch level of the application servers being used and can be upgraded independently (the SAP Web Dispatcher is downward-compatible and can therefore also be used for older systems).As of Release 7.10, the SAP Web Dispatcher must run in a separate directory.
We recommend that you install the Web Dispatcher as a separate system via the SAP installation.
Alternatively to a normal installation, you can also unpack the contents of the archive SAPWEBDISP.SAR into a separate directory, for example
Windows: C:\Program Files\< SID >\SAPWebDisp
UNIX: /usr/sap/<SID>/sapwebdisp
Create the directory and unpack SAPWEBDISP. SAR into this directory. Make sure that there are no other files in the directory.
You must set the parameter DIR_EXECUTABLE in the instance profile of the Web Dispatcher to the selected directory.You can use “sapwebdisp -v” to determine the version installed:
For example, SAP Web Dispatcher Version 7.00. 3, multithreaded, ASCIIThe SAP Web Dispatcher writes any errors that occur into the
“dev_webdisp” file in the current work directory.
Information about SAP Web Dispatcher Version 6.40 and higher
The system files msvcp71.dll and msvcr71. dll must exist in your system to execute the Web Dispatcher on Windows. These files may be missing on older systems, in which case the program cannot be started. In this case, see SAP Note 684106 “Microsoft Runtime DLLs”.
Configuring the SAP Web Dispatcher
The following parameters (with their default values in Version 6.40) restrict the maximum load on the Web Dispatcher:
icm/max_conn = 500
wdisp/HTTP/max_pooled_con = 100 and wdisp/HTTPS/max_pooled_con = 100
icm/req_queue_len = 500
icm/min_threads = 10
icm/max_threads = 50
mpi/total_size_MB = 80
mpi/max_pipes = 4000
Bear in mind that each active HTTP connection requires two memory pipes (therefore four event indicators) as well as two sockets. This is without yet mentioning the possible number of simultaneously active users, as a user can open several HTTP connections simultaneously depending on the particular application. You may have to change operating system parameters to allow for these types of high-load scenarios. For more information, see SAP Note 715400.
Relationship between users and active HTTP connections
To evaluate how many users can use the SAP Web Dispatcher, you must consider the following situations:Depending upon the application, a dialog step can open several HTTP requests. These are generally distributed among as many as four parallel connections. The user does not see exactly how many connections are opened. The average number of HTTP connections per request is indicated in the following formula with req_per_dialog_step.The “think time” is also a decisive factor affecting the utilization of the Web Dispatcher. This is the period of time (in seconds) between two dialog steps (”clicks”) executed by the user. There is no active HTTP connection during this time (this still depends on the timeout, see below). The think time is indicated in the formula with thinktime_per_diastep_sec.Another important factor here is the keepalive timeout (parameters icm/server_port_< xx > or icm/keep_alive_timeout), which defines how long the Web Dispatcher keeps the connection open for further requests. This timeout in seconds is indicated in the formula with conn_keepalive_sec.
Therefore, there is no global formula since the actual number of parallel HTTP connections concurrent_conn depends on the parameters. The following offers a rule of thumb:
concurrent_conn = (users * req_per_dialog_step * conn_keepalive_sec)/ (thinktime_per_diastep_sec)
You can use the mpi/total_size_MB formula to determine the total MPI size
mpi/total_size_mb = (concurrent_conn * mpi_buffer_size) / (1024 * 1024)
With 50 users, 3 requests per click, a keep_alive_timeout of 30 seconds (if the Web Dispatcher notices that resources are running out, it automatically sets the timeout for new connections) and an average think time of 20 seconds, the following maximum values result: concurrent_conn = 225 and mpi/total_size_MB = 14.
Therefore, the standard settings in the SAP Web Dispatcher are sufficient for this scenario.
With 500 users, 3 requests per click, a keep_alive_timeout of 60 seconds and a think time of 20 seconds, the following maximum values result:
concurrent_conn = 4500 and mpi/total_size_MB = 281.
With 1,000 users, 3 requests per click, a keep_alive_timeout of 30 seconds and a think time of 20 seconds, the following maximum values result:
concurrent_conn = 4500 and mpi/total_size_MB = 281.
With 12,000 users, 3 requests per click, a keep_alive_timeout of 5 seconds and a think time of 30 seconds, the following maximum values result:
concurrent_conn = 6000 and mpi/total_size_MB = 375.
Maximum parameter values for Version 6.40:
icm/max_conn = 8192 or > concurrent_conn
icm/max_sockets = 16384 or > 2 * concurrent_conn
wdisp/HTTP/max_pooled_con = 8000 or wdisp/HTTPS/max_pooled_con = 8000
icm/req_queue_len = 6000
icm/min_threads = 100
icm/max_threads = 200
mpi/total_size_MB = 500
mpi/max_pipes = 20500
Minimum parameter values:
mpi/buffer_size = 32768
In the parameter icm/server_port_< XX >, you have the option of entering the parameter HOST=<Host name or IP address> to ensure that the port is only connected to a specific host name, and not to all host names (as is the default setting). If you want to run an IIS on the same host in addition to the Web Dispatcher, and want both programs to listen to the same port, you must make sure that you make the appropriate settings in the IIS. If you do not, the IIS listens to all available ports.Note the following:
Depending on the log used between the SAP Web Dispatcher and the application server, either connections from the HTTP pool or HTTPS pool are used. Therefore, the maximum number of parallel connections must be increased either with the wdisp/HTTP/max_pooled_con parameter (for HTTP) or with the wdisp/HTTPS/max_pooled_con parameter (for HTTPS).Connections using the ROUTER log at the Web Dispatcher always use connections from the HTTPS pool.HTTP and ssl_encrypt = 0 or 1 (no encryption for the Application Server) use the HTTP pool or HTTPS pool.HTTPS and ssl_encrypt = 0 (no encryption for the AppServer) use the HTTP pool or HTTPS pool.

Operating system dependencies:

Note that the operating systems often have restrictions for the maximum number of open file handles (sockets) for each process. Check that each process can have at least as many sockets (file handles) as is specified in the icm/max_sockets parameter (default is 2048).
At startup, the Web Dispatcher (and ICM) checks whether it can receive sufficient sockets from the operating system. If not, the trace file displays the following record:
[Thr 1] *** WARNING => maximum number of sockets supported on this host (1019) less than parameter icm/max_sockets (8192) [icxxrout_mt. 227]
You should then check the settings in the operating system:
AIX
You can use the “ulimit -n” command to obtain the current value for the maximum number of open sockets (default: 2000). Using the command ‘chuser nofiles=<new value> <User>’, the value can be changed for the user.
SUN Solaris
Use the ‘limit’ command to check the value of “descriptors” in the csh shell. You can also use the ‘limit’ command to change the value (further information is available under ‘man limit’).
HP UX
The “maxfiles”, “maxfiles_lim” and “nfile” kernel parameters exist which are used to define the maximum open file handles. For PA-Risc, the parameter with SAM -> kernel configuration with kcweb should be changed.
Further information is available at: http://docs.hp. com/hpux/onlinedocs/939/KCParms/KCparamTut.OpenLockedFiles.html
Tru64 UNIX
In Tru64 UNIX, processes are limited by the open_max_hard (default 4096) and open_max_soft (default 4096) kernel parameters (both of these are defined in the proc kernel subsystem). In the entire system, the number is limited by the max_vnodes kernel parameter (kernel subsystem vfs).
The process of changing parameters in the system is described in Note 356370.
Windows platforms
Check the Windows Registry settings with regedt32:
My_Computer\HKEY_LOCAL_MACHINE\SYSTEMN\CurrentControlSet\Services\Tcpip\Parameters:
MaxUserPort should be at least 0xfde8 = 65000
TcpTimedWaitDelay should be 0×1e = 30 (or less)
See also: http://www.microsoft.com/resources/documentation/Windows/2000/server/reskit/en-us/Default.asp?url=/resources/documentation/Windows/2000/server/reskit/en-us/regentry/58791.asp
Linux
You can use the “ulimit -n” command to obtain the current value for the maximum number of open sockets (default: 1024). You must adapt the nofile parameter in the /etc/security/limits.conf configuration file.
AS/400
The standard value for the maximum number of open sockets is approximately 2000. However, if required, you can use an operating system API to increase this number. Due to a sequence problem, the system requests the maximum number of sockets BEFORE you know how many sockets the Web Dispatcher requires. This number must be determined before the system can call the above-mentioned API to increase the required number of sockets from the operating system.
The Web Dispatcher does not contain enough sockets only if this call fails. If NO error message of the following type occurs in the following four lines of the dev_webdisp, you can therefore ignore the warning that refers to the maximum number of sockets in AS/400.
“SiInit: o4_setmaxfh failed” occurs in the following four lines of the dev_icm, you can therefore ignore the warning that refers to the maximum number of sockets in AS/400.

6.40 Change history:

Details about the change history are now available in Note 908160.

SAP Web Dispatcher Documentation

The SAP Web Dispatcher is downward-compatible and we recommend that you always use the latest version.
Release 7.1
The documentation for SAP Web Dispatcher 7.10 is available on the help.sap.com Help Portal under
Documentation -> SAP NetWeaver PI/Mobile 7.1. Select the relevant language.
In the SAP Library, select
SAP NetWeaver Library -> Function-Oriented View -> Application Server Infrastructure -> SAP Web Dispatcher.
Release 7.0
The documentation for SAP Web Dispatcher 7.0 is available on the help.sap.com Help Portal under
Documentation -> SAP NetWeaver -> SAP NetWeaver 7.0 (2004s). Select the relevant language.
In the SAP Library, select
SAP NetWeaver Library -> Key Functional Areas of SAP NetWeaver -> Key Functional Areas of the Solution Life Cycle Management -> System Management -> SAP Web Dispatcher.
Release 6.40
The documentation for SAP Web Dispatcher 6.40 is available on the help.sap.com Help Portal under
Documentation -> SAP NetWeaver -> SAP NetWeaver 2004. Select the language.
In the SAP Library, select
SAP NetWeaver -> Solution Lifecycle Management -> System Management -> SAP Web Dispatcher.

More information
Information about the technical infrastructure is available on SAP Service Marketplace at http://service.sap.com/installNW70. After you select the relevant SAP NetWeaver release on the left hand side of the page, a link to the “Technical Infrastructure Guide” is provided on the right hand side of the page in the “Planning” section.A How-to Guide about “How To Configure SAP Web Dispatcher for SSL” is provided on SDN at the following address: https://www.sdn.sap.com/irj/sdn/howtoguides under “SAP Web Application Server”.A VC session on the subject is available at: http://service.sap.com/~sapidb/011000358700008521582002.vcm