Standby Server
hot_standby
Parameter description: Specifies whether to allow connections and queries on a standby server during its recovery.
This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.
NOTICE:
- If this parameter is set to on, wal_level must be set to hot_standby. Otherwise, the database startup fails.
- In an HA system, hot_standby cannot be set to off, because this setting can affect other features of the HA system.
- If the hot_standby parameter was disabled and the wal_level parameter was set to a value lower than hot_standby, perform the following operations to ensure that the logs to be replayed on the standby node can be queried on the standby node before enabling the hot_standby parameter again:
- Change the wal_level value of the primary and standby nodes to hot_standby or higher, and restart the instances for the change to take effect.
- Perform the checkpoint operation on the primary node and query the pg_stat_get_wal_senders() function to ensure that the receiver_replay_location value of each standby node is the same as the sender_flush_location value of the primary node. Ensure that the value adjustment of wal_level is synchronized to standby nodes and takes effect, and standby nodes do not need to replay low-level logs.
- Set the hot_standby parameter of the primary and standby nodes to on, and restart the instances for the setting to take effect.
Value range: Boolean
- on indicates that connections and queries are allowed on the standby server during the recovery.
- off indicates that connections and queries are not allowed on the standby server during the recovery.
Default value: on
max_standby_archive_delay
Parameter description: Specifies the wait period before queries on a standby server are canceled when the queries conflict with WAL processing and archiving in hot standby mode.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from –1 to *INT*MAX_. The unit is ms.
Default value: 3s (3000 ms)
max_standby_streaming_delay
Parameter description: Specifies the wait period before queries on a standby server are canceled when the queries conflict with WAL data receiving through streaming replication in hot standby mode.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from –1 to *INT*MAX_. The unit is ms.
Default value: 3s (3000 ms)
wal_receiver_status_interval
Parameter description: Specifies the maximum interval for notifying the primary server of the WAL Receiver status.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 0 to INT_MAX. The unit is ms.
Default value: 5s (5000 ms)
hot_standby_feedback
Parameter description: Specifies whether a standby server is allowed to send the result of a query performed on it to the primary server, preventing a query conflict.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: Boolean
- on indicates that the ID of the oldest transaction active on standby servers will be sent to the primary server.
- off indicates that the ID of the oldest transaction active on standby servers will not be sent to the primary server.
Default value: off
wal_receiver_timeout
Parameter description: Specifies the maximum wait period for a standby server to receive data from the primary server.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 0 to *INT*MAX_. The unit is ms.
Default value: 6s (6000 ms)
wal_receiver_connect_timeout
Parameter description: Specifies the timeout period for a standby server to connect to the primary server.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 0 to *INT*MAX_/1000. The unit is s.
Default value: 2s
wal_receiver_connect_retries
Parameter description: Specifies the maximum attempts that a standby server connects to the primary server
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 1 to *INT*MAX_
Default value: 1
wal_receiver_buffer_size
Parameter description: Specifies the size of the memory buffer that stores the Xlogs received by the standby and secondary nodes. Currently, primary/standby/secondary deployment is not supported by default.
This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 4096 to 1047552. The unit is KB.
Default value: 64 MB (65536 KB)
primary_slotname
Parameter description: Specifies the slot name of the primary server corresponding to a standby server. This parameter is used for the mechanisms to verify the primary-standby relationship and delete WALs.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: a string
Default value: empty
max_logical_replication_workers
Parameter description: Specifies the maximum number of apply worker threads on the subscriber side.
This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 0 to 262143
Default value: 4
max_sync_workers_per_subscription
Parameter description: Specifies the maximum number of tablesync worker threads for each subscription on the subscriber side.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 0 to 262143
Default value: 2