Resource Impact on SMP Performance
The SMP architecture uses abundant resources to obtain time. After the plan parallelism is executed, the resource consumption is added, including the CPU, memory, I/O, and network bandwidth resources. As the parallelism degree is expanded, the resource consumption increases. If these resources become a bottleneck, the SMP cannot improve the performance and the overall cluster performance may be deteriorated. The following information describes the situations that the SMP affects theses resources:
- CPU resources
In a general customer scenario, the system CPU usage rate is not high. Using the SMP parallelism architecture will fully use the CPU resource to improve the system performance. If the number of CPU kernels of the database server is too small and the CPU usage is already high, enabling the SMP parallelism may deteriorate the system performance due to resource compete between multiple threads.
- Memory resources
After queries are performed concurrently, the memory usage increases. However, the upper limit of the memory usage of each operator is limited by the resource management module. If the system memory is insufficient, data may be saved to disks after queries are concurrently performed. As a result, the query performance deteriorates.
- Network bandwidth resources
To execute a query in parallel, data exchange operators are added. Local Stream operators exchange data between threads within a DN. Data is exchanged in memory and network performance is not affected. Non-Local operators exchange data over the network and increase network load. If the capacity of a network resource becomes a bottleneck, parallelism may also increase the network load.
- I/O resources
A parallel scan increases I/O resource consumption. It can improve performance only when I/O resources are sufficient.
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