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 GUC parameters.

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:
  1. 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.
  2. 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.
  3. 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 GUC parameters.

NOTICE:

-1 indicates that the standby server waits until the conflicting queries are complete.

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 GUC parameters.

NOTICE:

-1 indicates that the standby server waits until the conflicting queries are complete.

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 GUC parameters.

Value range: an integer ranging from 0 to INT_MAX. The unit is ms.

Default value: 5s (5000 ms)

NOTICE: If this parameter is set to 0, the standby server does not send information, such as the log receiving location, to the primary server. As a result, the transaction commit on the primary server may be blocked, and the switchover may fail. In normal service scenarios, you are not advised to set this parameter to 0.

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 GUC parameters.

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

NOTICE:

If this parameter is set to on, VACUUM on the primary server will not clean up tuples modified in transactions later than the oldest transaction active on standby servers. Therefore, the performance of the primary server will be affected.

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 GUC parameters.

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 GUC parameters.

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 GUC parameters.

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 GUC parameters.

Value range: an integer ranging from 4096 to 1047552. The unit is kB.

Default value: 64MB (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 GUC parameters.

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 GUC parameters.

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 GUC parameters.

Value range: an integer ranging from 0 to 262143

Default value: 2

pgxc_node_name

Parameter description: Specifies the name of a node.

This parameter is a POSTMASTER parameter. Set it based on Table 1 GUC parameters.

When a standby node requests to replicate logs on the primary node, if the application_name parameter is not set, the pgxc_node_name parameter is used as the name of the streaming replication slot of the standby node on the primary node. The streaming replication slot is named in the following format: Value of this parameter_IP address of the standby node_Port number of the standby node. The IP address and port number of the standby node are obtained from the IP address and port number of the standby node specified by the replconninfo parameter. The maximum length of a streaming replication slot name is 61 characters. If the length of the concatenated string exceeds 61 characters, the truncated pgxc_node_name will be used for concatenation to ensure that the length of the streaming replication slot name is less than or equal to 61 characters.

Note: After this parameter is modified, the database instance will fail to be connected. You are advised not to modify this parameter.

Value range: a string

Default value: current node name

protect_standby

Parameter description: This parameter is used to control whether the standby node role is protected.

This parameter is a SIGHUP parameter. Set it based on Table 1 GUC parameters.

Value range: Boolean

• on means that the standby node cannot be upgraded or downgraded to a cascaded standby by using the failover or switchover command.
• off means that the standby node role is unprotected and can be upgraded or downgraded to a cascaded standby.

Default value: off

Note：

• If you need to configure the standby node to refuse to raise the master, you can set the protect_standby parameter to on; if you need to raise the master of this database, you should modify the protect_standby parameter to off first, and then raise the master of this database after executing reload.
• This parameter does not take effect for the primary node or cascade backup. This parameter does not take effect on the primary node or cascade backup. It does not change with the value of the primary node parameter.
• By default, dcf is not supported. If dcf is encountered, the check of protect_standby will be skipped.