Maximum number of APPC active conversations

Each APPC conversation on the system uses a small amount of APPC system resources in order to execute. If a single address space has a serious programmatic or logical error or if the workload volume is enormous, a tremendous number of active conversations within a single address space could result. Consequently, vast quantities of APPC system resources could be consumed, exhausting the ability of APPC to start up conversations in other address spaces. APPC on z/OS® provides a mechanism which will notify an installation of such an event, and allow them to take the appropriate actions to fix this potentially crippling situation.

This function defines the maximum number of APPC active conversations that can be active in any particular address space at one time. The system either writes a critical action message to the console whenever an address space exceeds this maximum, or optionally, halts all new conversations within the address space when the limit has been reached.

To define the maximum number of active conversations, use the CONVMAX parameter in the APPC started procedure in specify the value for the maximum number of active conversations. Use one of the following methods:

Specify a value for the CONVMAX parameter on the PROC statement.
For example, if you want to set maximum of APPC active conversation as 3000, specify the following:
```
     //  APPC PROC APPC=00,CONVMAX=3000
```
In the exec statement set, CONVMAX=&CONVMAX as follows:
```
     //  EXEC PGM=ATBINITM,PARM="APPC=&APPC,CONVMAX=&CONVMAX....."
```
If you use this method, you can specify CONVMAX=xx on the START APPC command to change the CONVMAX value.
Define a fixed value for the CONVMAX parameter on the EXEC statement. For example, if you want to set 3000 as the maximum number of APPC active conversations, specify the following:
```
     //  EXEC PGM=ATBINITM,PARM="APPC=&APPC,CONVMAX=3000..."
```
Let APPC/MVS use the default value for CONVMAX, which is 2000. Code the exec statement as follows:
```
     //  EXEC PGM=ATBINITM,PARM="APPC=&APPC..."
```
When specifying the maximum number of APPC active conversations on the CONVMAX parameter, keep the following in mind:
- The value must be a decimal value between 100 and 20000. If you specify a value greater than 20000, the system sets the maximum number of active conversations threshold to 20000. If you specify a value between 1 and 99, the system sets the maximum APPC conversations threshold to 100.
- If you specify a value of 0 (zero) the system will not monitor the total number of active conversations for an address space, regardless of the quantity.

To define the action appc should take when the CONVMAX limit has been reached, use the CMACTION parameter in the APPC started procedure in SYS1.PROCLIB. There are two possible values for the CONVMAX action parameter:

MSGONLY - cuts a critical action message whenever the number of active conversations in a single address space exceeds the CONVMAX value in effect on the system. APPC will not take any action on preventing new conversations from being started inside the affected address space. This is the default value.
HALTNEW - prevents new conversations from being started inside an address space once the CONVMAX value has been reached. A critical action message is also sent to the console to inform the installation that no new conversations will be allowed to be started until the until the number of active conversations within the address space decreases.

Specify one of two possible values for the CMACTION parameter using one of the following methods:

Specify a value of the CMACTION parameter on the PROC statement to either MSGONLY or HALTNEW. For example, specify the following if you want APPC to halt all new conversations in an address space when the CONVMAX has been reached for that address space:
```
  //    APPC PROC APPC=00,CMACTION=HALTNEW
```
Then, in the exec statement, set CMACTION=&CMACTION as follows:
```
//    EXEC PGM=ATBINITM,PARM='APPC=&APPC,
        CMACTION=&CMACTION...'
```
This method allow you to specify CMACTION=cmaction_value on the START APPC command to change the CMACTION value.
Define a fixed value for the CMACTION parameter on the EXEC statement. For example, if you want only to be informed when the number of APPC active conversations has been exceeded, specify the following:
```
//    EXEC  PGM=ATBINITM,PARM='APPC=&APPC,
        CMACTION=MSGONLY...'
```
Let APPC/MVS use the default value for CMACTION, which is HALTNEW. To do this, code the EXEC statement as follows:
```
//     EXEC  PGM=ATBINITM,PARM='APPC=&APPC...'
```