Adjusting the Operating System Shared Memory Parameters

Adjust shared memory segments if Adaptive Server cannot obtain large memory as a single segment or if Backup Server stripes fail due to insufficient segments.

Depending on the number and types of devices used for backup (dump) and recovery (load), you may need to adjust the shared memory segment parameter in the operating system configuration file to accommodate concurrent Backup Server processes. There are six default shared memory segments available for process attachments.

If any reconfiguration through sp_configure requires additional memory, Adaptive Server allocates shared memory segments after start-up. To account for these additional segments, allocate the maximum memory available to Adaptive Server by using the allocate max shared memory configuration parameter. See the System Administration Guide.

Adjust the operating system shared memory parameter.
For Adaptive Server to run, the operating system must be configured to allow allocation of a shared memory segment at least as large as the Adaptive Server total logical memory configuration parameter.

The default total logical memory parameter for HP is 32,768 2KB pages (64MB) on the 32-bit operating system, and 45,056 2KB pages (88MB) on the 64-bit operating system. To adjust the shared memory value of the operating system, use the System Administration Manager (SAM).
To adjust the shared memory value of the operating system, add the following lines to the operating system configuration file /etc/sysconfigtab:
```
ipc: shm-max=nnn
```
For HP and UNIX 5.0a, add:
```
ssm-threshold=0
```
If this parameter is not set, Adaptive Server does not start, and the following message is displayed:
```
os create region: shmat "xx": invalid argument
```
After installing Adaptive Server, you can change any configuration parameter, procedure cache, and data cache sizes. This may require that you increase the configuration parameter max memory.
To optimize asynchronous I/O and to prevent the paging of shared memory, you must grant MLOCK permissions before you install Adaptive Server. To grant MLOCK permissions to a group, enter:
```
/etc/privgrp add mlock <group name>
```
or:
```
/etc/setprivgrp <group name> MLOCK
```