Log Replay

recovery_time_target

Parameter description: Specifies the time for a standby server to write and replay logs.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to 3600. The unit is s.

0 indicates that log flow control is disabled. A value from 1 to 3600 indicates that a standby server can write and replay logs within the period specified by the value, so that the standby server can quickly assume the primary role. If this parameter is set to a small value, the performance of the primary server is affected. If it is set to a large value, the log flow is not effectively controlled.

Default value: 60

recovery_max_workers

Parameter description: Specifies the maximum number of concurrent replay threads.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to 20

Default value: 4

recovery_parallelism

Parameter description: Specifies the actual number of replay threads. This parameter is read-only.

This parameter is a POSTMASTER parameter and is affected by recovery_max_workers and recovery_parse_workers. If any value is greater than 0, recover_parallelism will be recalculated.

Value range: an integer ranging from 1 to 2147483647

Default value: 1

recovery_parse_workers

Parameter description: Specifies the number of ParseRedoRecord threads for the extreme RTO feature.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to 16

This parameter can be set to a value greater than 1 only when the extreme RTO feature is enabled. In addition, it must be used together with recovery_redo_workers. If both recovery_parse_workers and recovery_max_workers are enabled, the setting of recovery_parse_workers prevails and the concurrent replay function is disabled. The ultimate RTO does not support primary/standby/secondary mode. The value of recovery_parse_workers can be greater than 1 only when replication_type is set to 1. In addition, when ultimate RTO is enabled, ensure that the value of wal_receiver_buffer_size is greater than or equal to 32 MB (64 MB is recommended). This feature does not support column-store tables, either. Therefore, disable this feature in a system where column-store tables are used or are to be used.

Default value: 1

• After V500R001C00 is upgraded to V500R001C10 or a later version, you are advised to set this parameter to 2 and restart the DN.
• After ultimate RTO is enabled, the standby node will start more worker threads whose value is equal to the value of recovery_parse_workers x (the value of recovery_redo_workers + 2) + 5, occupying more CPU, memory, and I/O resources. In hybrid deployment scenarios, host performance may be affected.
• In this version and later, the ultimate RTO does not have flow control. Flow control is controlled by the recovery_time_target parameter.

recovery_redo_workers

Parameter description: Specifies the number of PageRedoWorker threads corresponding to each ParseRedoRecord thread when the ultimate RTO feature is enabled.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to 8

This parameter must be used together with recovery_parse_workers, and it takes effect only when recovery_parse_workers is set to a value greater than 1.

Default value: 1

After V500R001C00 is upgraded to V500R001C10 or a later version, you are advised to set parameters based on the number of CPUs in the environment and restart the DN. If the number of CPUs is less than 16, you are advised to set this parameter to 2. If the number is greater than 16 and less than 32, you are advised to set this parameter to 4. If the number is greater than 32, you are advised to set this parameter to 8.

enable_page_lsn_check

Parameter description: Specifies whether to enable the data page LSN check. During replay, the current LSN of the data page is checked to see if it is the expected one.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

Default value: on

redo_bind_cpu_attr

Parameter description: Specifies the core binding operation of the replay thread. Only the sysadmin user can access this parameter. This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: a string, consisting of one or more characters

The available configuration modes are as follows: 1. 'nobind': The thread is not bound to a core. 2. 'nodebind: 1, 2': Use the CPU cores in NUMA groups 1 and 2 to bind threads. 3. 'cpubind: 0-30': Use the CPU cores 0 to 30 to bind threads. The value of this parameter is case-insensitive.

Default value: 'nobind'

This parameter is used for core binding in the ARM environment. You are advised to bind all replay threads to the same NUMA group for better performance. In hybrid deployment scenarios, you are advised to bind the replay threads of different nodes on the same host to different NUMA groups.