This section describes parameter settings and value ranges for communication libraries.
comm_max_datanode
Parameter description: Specifies the maximum number of DNs supported by the communication library.
Type: USERSET
Value range: an integer ranging from 1 to 8192
Default value: actual number of DNs
If the number of DNs is increased, the change takes effect immediately. If the number of DNs is reduced, the cluster needs to be restarted for the change to take effect.
comm_max_stream
Parameter description: maximum number of logical connection data structures cached in the communication library.
Type: SIGHUP
Value range: an integer ranging from 1 to 65535
Default value: 1024
If the value of comm_max_datanode is small, the process memory is sufficient. In this case, you can increase the value of comm_max_stream.
max_stream_pool
Parameter description: Specifies the maximum number of stream threads that can be contained in a stream thread pool. This feature is supported in 8.1.2 or later.
Type: SUSET
Value range: an integer ranging from -1 to INT_MAX. The values -1 and 0 indicate that the stream thread pool is disabled.
Default value: 65535
- The number of stream threads in a thread pool can be reduced in real time. If the value of this parameter is increased, the number of stream threads is increased to meet the service requirements.
- Generally, you are advised not to change the value of this parameter because the stream thread pool supports the automatic cleanup function.
- If too many idle stream threads occupy the memory, you can decrease the value of this parameter to save the memory.
enable_stream_sync_quit
Parameter description: whether the stream threads exit synchronously when the stream plan ends. This parameter is supported only by clusters of version 8.2.1.300 or later.
Type: USERSET
Value range: Boolean
- on indicates that threads in the stream thread group exit after the steam plan ends.
- off indicates that stream threads exit directly after the stream plan ends without waiting for the threads in the stream thread group to exit.
Default value: off
comm_max_receiver
Parameter description: Specifies the number of internal receiving threads of the communication library.
Type: POSTMASTER
Value range: an integer ranging from 1 to 50
Default value: 4
comm_quota_size
Parameter description: Specifies the maximum size of packets that can be continuously sent by the communication library. When you use a 1GE NIC, a small value ranging from 20 KB to 40 KB is recommended.
Type: USERSET
Value range: an integer ranging from 0 to 102400. The default unit is KB. The value 0 indicates that the quota mechanism is not used.
Default value: 1 MB
comm_usable_memory
Parameter description: Specifies the maximum memory that can be used by the communication library cache on a single DN.
Type: SIGHUP
Value range: an integer ranging from 1 to 256. The default unit is KB. The minimum size cannot be less than 1 GB for installation.
Default value: max_process_memory/8
This parameter must be specifically set based on environment memory and the deployment method. If it is too large, out-of-memory (OOM) may occur. If it is too small, the performance of the communication library may deteriorate.
comm_memory_pool_percent
Parameter description: Specifies the percentage of the memory pool resources that can be used by the communication library on a DN. This parameter is used to adaptively reserve memory used by the communication libraries.
Type: POSTMASTER
Value range: an integer ranging from 0 to 100
Default value: 0
If the memory used by the communication library is small, set this parameter to a small value. Otherwise, set it to a large value.
comm_client_bind
Parameter description: Specifies whether to bind the client of the communication library to a specified IP address when the client initiates a connection.
Type: USERSET
Value range: Boolean
- on indicates that the client is bound to a specified IP address.
- off indicates that the client is not bound to any IP addresses.
If multiple IP addresses of a node in a cluster are on the same communication network segment, set this parameter to on. In this case, the client is bound to the IP address specified by listen_addresses. The concurrency performance of a cluster depends on the number of random ports because a port can be used only by one client at a time.
Default value: off
comm_no_delay
Parameter description: Specifies whether to use the NO_DELAY attribute of the communication library connection. Restart the cluster for the setting to take effect.
Type: USERSET
Value range: Boolean
Default value: off
If packet loss occurs because a large number of packets are received per second, set this parameter to off to reduce the total number of packets.
comm_debug_mode
Parameter description: Specifies the debug mode of the communication library, that is, whether to print logs about the communication layer. The setting is effective at the session layer.
When the switch is set to on, the number of printed logs is huge, adding extra overhead and reducing database performance. Therefore, set the switch to on only in the debug mode.
Type: USERSET
Value range: Boolean
- on indicates the detailed debug log of the communication library is printed.
- off indicates the detailed debug log of the communication library is not printed.
Default value: off
comm_ackchk_time
Parameter description: Specifies the duration after which the communication library server automatically triggers ACK when no data package is received.
Type: USERSET
Value range: an integer ranging from 0 to 20000. The unit is millisecond (ms). 0 indicates that automatic ACK triggering is disabled.
Default value: 2000
comm_timer_mode
Parameter description: Specifies the timer mode of the communication library, that is, whether to print timer logs in each phase of the communication layer. The setting is effective at the session layer.
When the switch is set to on, the number of printed logs is huge, adding extra overhead and reducing database performance. Therefore, set the switch to on only in the debug mode.
Type: USERSET
Value range: Boolean
- on indicates the detailed timer log of the communication library is printed.
- off indicates the detailed timer log of the communication library is not printed.
Default value: off
comm_stat_mode
Parameter description: Specifies the stat mode of the communication library, that is, whether to print statistics about the communication layer. The setting is effective at the session layer.
When the switch is set to on, the number of printed logs is huge, adding extra overhead and reducing database performance. Therefore, set the switch to on only in the debug mode.
Type: USERSET
Value range: Boolean
- on indicates the statistics log of the communication library is printed.
- off indicates the statistics log of the communication library is not printed.
Default value: off
enable_stateless_pooler_reuse
Parameter description: Specifies whether to enable the pooler reuse mode. The setting takes effect after the cluster is restarted.
Type: POSTMASTER
Value range: Boolean
- on or true indicates that the pooler reuse mode is enabled.
- off or false indicates that the pooler reuse mode is disabled.
Set this parameter to the same value for CNs and DNs. If enable_stateless_pooler_reuse is set to off for CNs and set to on for DNs, the cluster communication fails. Restart the cluster to make the setting take effect.
Default value: off
comm_cn_dn_logic_conn
Parameter description: Specifies a switch for logical connections between CNs and DNs. The parameter setting takes effect only after the cluster is restarted.
Type: POSTMASTER
Value range: Boolean
- on or true indicates that the connections between CNs and DNs are logical, with the libcomm component in use.
- off or false indicates that the connections between CNs and DNs are physical, with the libpq component in use.
If comm_cn_dn_logic_conn is set to off for CNs and set to on for DNs, cluster communication will fail. You are advised to set this parameter to the same value for all CNs and DNs. Restart the cluster to make the setting take effect.
Default value: off
client_connection_check_interval
Parameter description: Specifies the interval for checking the client connection status. This parameter is supported by version 8.2.0 or later clusters.
Type: USERSET
Value range: an integer ranging from 0 to INT_MAX. The unit is ms. The value 0 indicates that the client connection status is not checked.
Default value: 10000
During a long query executed in a session where a client (such as gsql, JDBC, or ODBC) directly connects to the CN,
- The CN checks the client connection status at the interval specified by client_connection_check_interval. If it detects that the client has been disconnected from the CN, the server terminates the long query and releases related resources to avoid waste of cluster resources.
- The DN checks its connection to the CN at the interval specified by client_connection_check_interval. If the DN detects that it has been disconnected from the CN, it terminates the long query and releases related resources to avoid waste of cluster resources.
conn_recycle_timeout
Parameter description: the interval for reclaiming idle connections between a CN and other nodes to the connection pool. This parameter is supported only by clusters of version 8.2.1 or later.
Type: USERSET
Value range: an integer ranging from 0 to 3600, in second (s). 0 indicates that the function of reclaiming idle connections is disabled.
Default value: 30