The syntax for starting Backup Server with the -m parameter is, where nnn is the maximum amount of shared memory in megabytes that the Backup Server can use for all of its dump or load sessions:
backupserver [-m nnn]
The -m parameter sets the upper limit for shared memory usage. However, Backup Server may use less memory than specified if it detects that adding more memory will not improve performance.
Backup Server determines the amount of shared memory available for each stripe by dividing the -m value by the configured number of service threads (-P parameter).
The default value for -m is the number of service threads multiplied by 1MB. The default value for -P is 48, so the default maximum shared memory utilization is 48MB. However, Backup Server reaches this usage only if all the 48 service threads are active concurrently. The maximum value for -P is the maximum number of service threads, 12,288. (For more information about -P, see “Configuring user-defined roles”.)
The amount of shared memory per stripe available for Backup Server is inversely proportional to the number of service threads you allocate. If you increase the maximum number of service threads, you must increase the -m value, also, to maintain the same amount of shared memory per stripe. If you increase the -P value but do not increase the -m value, the shared memory allocated per stripe can decrease to the point that the dump or load cannot be processed.
To determine how much to increase the -m value, use this formula:
(-m value in MB) * 1024/(-P value)
If the value obtained by this formula is less than 128KB, Backup Server will not start.
The minimum value for -m is 6MB. The maximum value for -m depends on operating system limits on shared memory.
If you create a dump using a Backup Server with a high shared memory value, and attempt to load the dump using a Backup Server with a lower shared memory value, Backup Server uses only the available memory. This results in degradation of the load performance.
If the amount of shared memory available per stripe at load time is less than twice the block size used at dump time, Backup Server aborts the load with an error message.
