Starting from this version, SMP auto adaptation is enabled. For newly deployed clusters, the default value of query_dop is 0, and SMP parameters have been adjusted. To ensure forward compatibility, the value of query_dop should remain unchanged after an existing cluster is upgraded.
For an upgraded cluster, if you want to set query_dop to 0 and enable SMP parallel processing, modify the following parameters to obtain better dop options:
- comm_usable_memory
If the system memory is large, the value of max_process_memory is large. In this case, you are advised to set the value of this parameter to 5% of max_process_memory, that is, 4 GB by default.
- comm_max_stream
The recommended value for this parameter is calculated as follows: comm_max_stream = Min(dop_limit x dop_limit x 20 x 2, max_process_memory (bytes) x 0.025/Number of DNs/260). The value must be within the value range of comm_max_stream.
- max_connections
The recommended value for this parameter is calculated as follows: max_connections = dop_limit x 20 x 6 + 24. The value must be within the value range of max_connections.
In the preceding formulas, dop_limit indicates the number of CPUs corresponding to each DN in the cluster. It is calculated as follows: dop_limit = Number of logical CPU cores of a single server/Number of DNs of a single server.