max online engines places an upper limit of the number of engine threads that can be brought online. It does not take into account the number of CPUs available at start-up, and allows users to add CPUs at a later date.
|
Summary Information |
|
|---|---|
|
Default value |
1 |
|
Range of values |
1 – 1024 (threaded mode) 1 – 128 (process mode) |
|
Status |
Static |
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Display level |
Intermediate |
|
Required role |
System administrator |
|
Configuration groups |
Memory Use, Processors |
See System Administration Guide: Volume 2 > Managing Mulitprocessor Servers for a detailed discussion of how to set this parameter for your SMP environment.
The following is the sequence of events at SAP ASE start-up:
System databases are recovered on engine 0.
SAP ASE accepts user connections.
All engines that are configured to be online during start-up are brought online.
User databases are recovered in parallel by a “self-tuned” number of recovery tasks using the default data cache tuned for optimal recovery performance.
Never have more engine threads online than there are CPUs.
max engines online must be large enough to allow SAP ASE to bring all the engine thread pools online simultaneously.
Depending on overall system load (including applications other than SAP ASE), you may achieve optimal throughput by leaving some CPUs free to run non-SAP ASE processes.
You can achieve better throughput by running fewer engine threads with high CPU use, rather than by running more engine threads with low CPU use.
Scalability is application-dependent. Conduct extensive benchmarks on your application to determine the best configuration of online engine threads.
In process mode, use sp_engine to take engine threads offline or to bring them online. You can take all engine threads offline except engine zero.
See Performance and Tuning Series: Basics > Using Engines and CPUs.