Recommended MAXUSERTASKS value

[Former Member]

If I have a system with potentially 800 users on SAP, what should I set the MAXUSERTASKS value to ? The server has 12 GB RAM and 4 CPU. Does this mean that if all 800 users are logged in to SAP, there will be 800 connections to MAXDB, hence it will require the MAXUSERTASKS to be set to at least 800 ? Other than the memory required (800 x 1024kb (TASK_STACK) = 800 MB), is there any other negative impact or is 800 too much ?

[former_member229109 · Accepted solution]

Hello Pranil,

With the database parameter MAXUSERTASKS you configure the maximum number of simultaneously active users (database sessions). If this number has been reached, then no other user can log on to this database instance. If you choose a very high value for MAXUSERTASKS, the database system requires a lot of address space, particularly for local communication via shared memory. Do not configure MAXUSERTASKS higher than necessary because the system needs a log of address space (especially shared memory) for it.

< http://dev.mysql.com/doc/maxdb/maxdb_faq.html >

Each usertask needs MAXTASKSTACK KB of memory. The value for MAXTASKSTACK depends on the operating system and the version used (are you using 7.6 ?).

-> What is the version of your database?

If you are SAP customer please review the SAP notes::

628131 SAP DB / MaxDB operating system parameters on Unix

757914 -9807 Task Limit

767635 MaxDB Version 7.5 parameter settings for OLTP/BW

806690 Feature list of liveCache/MaxDB 7.6

846890 FAQ: MaxDB Administration

***

For the liveCache database instance < LVC type > you will have different recommendations, please review the SAP Note No. 719652 to see recommended values for the parameter MAXUSERTASKS for the liveCache instance.

Thank you and best regards, Natalia Khlopina

[Former Member · Accepted solution]

Thanks Natalia,

We are using 7.6. I have had a look at the SAP notes you mentioned, but couldn't find a clear answer.

On one hand, each UKT takes memory space (I read somewhere is about 1024kb), so for 800 users, it would be about 800 MB, but on the other hand, if the MAXUSERTASKS is too low, some users won't be able to connect.

I guess it all depends on how persistant a UKT is for a user. If a user logs in to SAP, is there a dedicated database connection maintained throughout the session (ie is a UKT created and maintained for the duration of just the particular user) or do the UKTs belong to a pool from where, it is assigned to a user only when data needs to be retreived or written to the database.

If I set the MAXUSERTASKS as 100, does this mean only 100 users can log in to SAP GUI or does it mean 500 people can log in and they will utilize one of the 100 UKTs only when required (provided all 500 of them do not read or write to the database simulatneously). Would be good to know what kind of values other sites of simliar user base (1000) set for this.

Regards..

[TTK · Accepted solution]

Hello Pranil

A few comments:

1. When running a SAP system, the user count of the SAP system and of the database do not coincide.

2. MAX_USER_TASKS can be adjusted after installing the data base. However, the data base has to be restarted. I.e. you can in-/decrease it if necessary.

3. When a SAP-user connects usually a connection to the data base is reused.

4. If you roughly know the amount of concurrent users of your system, use this number as first guess for MAX_USER_TASK.

Regards Thomas

[Former Member]

Thanks, I'll try it with a lower setting and see how it goes.