DIALOG INSTANCE

[Former Member]

HI,

What is the use of dialog instance? But there is already central instance (operates sap system) where the user login and access the sap system.

Please let me know in simpler definition

[Former Member · Accepted solution]

Hi Kevin,

In simple terms you can have more than one dialog instance with ur CI(central instance).The basis diff between the two is Central Instance has message server on the other hand Dailog Instance does not have that. We use Dialog instances to distribute the load from the CI(Central Instance). For example you have 450 users and load on CI is very high becoz at a time all the users will get connected to the CI so just to reduce the load you can have 4 dialog instances connected to CI and each DI can have 100 users.In this way load from the Central Instance(which contains the database) will be reduced.

I hope this explanation will help you.

Regards,

Prashant

[Former Member · Accepted solution]

To add to what Prashant has mentioned:

A Central instance has a message serer and an enque work process(ENQ) for exclusive database locks to avoid concurrent changes to the same data by different users.

Regards,

Ashutosh

[Former Member · Accepted solution]

Thanks, As dialog instance is meant for load balancing ,it is also a sap system where the users can loggin.But my question is ,from my understanding the development of the system take place in central instance( within the clients) and users are allowed to access the central instance for configuration ,development etc.If excess users are transferred to dialog instance, how the changes made in central instance take place in this system or dialog instance is replica of central instance?

Note: considering an instance as a sap system,eg: sap ecc.

[Former Member · Accepted solution]

Hello Kevin

Every system is identified by the three digits alphabets which is called SID ( eg DEV, QAS and PRD).

For example once u login to the DEV system to the client 100 ( for eg) no matter you are connected to central istance or dialogue instance you still have the access to the whole data.

Regards

Basis Dude.

[Former Member · Accepted solution]

Thanks.

Inorder to access the central instance,we need to know the IP of the host to login .Where as if there is 1 or more dialog instances for the central (e g: DEV) which are installed on the same machine or different machine,do we need to give different IP of the dialog instances to the end users? or just the IP of the central instance (DEV) in the sap gui and it automatically distributes the users internally to other dialog instances if there is overflow.

[debasissahoo · Accepted solution]

Hi Kelvin,

If you have two instances on one host, lets say 00 is the CI, 01 is the Dialog instance.

- You've the option of configuring logon load balancing, i.e. you create one logon group in SMLG tcode and assign the instaces (CI & DI) to the group. then if user login from the GUI through the logon group connection, then SAP's message server will take care of the logon load balancing i.e it will have the user logged on to the instance with less load. For more help on logon group,

http://help.sap.com/erp2005_ehp_03/helpdata/EN/c4/3a64b4505211d189550000e829fbbd/content.htm

- But if you want the user to login to the DI in specific, then they just need to give the same IP of CI and instance no. of the DI to login to the dialog instance. in this case if they give 01 as system no# that will distinguish from CI and they will connect to directly 3201 port i.e. dispatcher of the dialog instance.

Hope this clarifies your question.

Regards,

Debasis.

[Former Member · Accepted solution]

Thanks much.Hope will learn basis soon with the help of all you guysss.

[Former Member · Accepted solution]

Hi,

I understood if there is multiple instances then load balancing should be done.I assume the use of specific instance access is done only if there is just central instance and no dialog instances..because of less users access...But I read from your above reply that specific DI..whats the need for specifying DI for the user if there is CI. And how can I find the corresponding message server for the system?

[debasissahoo · Accepted solution]

Hi Kelvin,

Message server is one per SAP system, which resides with the CI. If there are multiple instances, load balancing can be done to equally distribute the load between them.

In special cases with large number of users and having multiple application servers, if you divide users according to applications like FI or MM connecting to respective application servers..(the advantage here is hit rates of buffers) either you may create multiple logon groups for specific applications or in some case, one dedicated application server may be for the group. In that case, they connect to one application server.

Follow this note which describes, setting up for logon group for automatic load balancing https://service.sap.com/sap/support/notes/26317

Regards,

Debasis.

[Former Member]

Hi Kevin,

Installation of additional dialog instance is used as a part of scalability of SAP system.

Eventhough you have central instance ( All types of WPs) and can login to the SAP system with but as the no of users increase you need to scale your system so that you can add more application servers ( Dialog instances) and cater to the increasing load in terms of no of users etc.

In short , dialog instance consists of set of WPs like DIA, BG

and will add to the SAP system resources.

Hope this is useful

Best Regards

Umesh

[Former Member]

Hello Kevin

Central instance is core of the SAP system, if the central instance is down, whole system is down.

Where as dialog instance (commonly known as the application server) is use to increase the Horse power of the System.

As Umesh says dialog instances are used for the load balancing the whole load ( all the users logged on and batch jobs) of the system.

I would like to mention a point, dialog instance increased the processing power as well, u can install a CI ( Central Instance) on a box X and you can install the dialog instance on y and one more isntance on box Z.

Box X has 3 CPUs and box Y and box Z has 5 cups each on ( 3 + 5 + 5 =13 CPUs) by this way by adding dialong instance you can increase the processing power of the sytem.

Hope this helps........

Regards

Basis Dude