Sending Server

max_wal_senders

Parameter description: Specifies the maximum number of simultaneously running WAL sender processes. The value cannot be greater than or equal to that of max_connections.

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

NOTICE: wal_level must be set to archive or hot_standby to allow the connection from standby servers.

Value range: an integer ranging from 0 to 262143

Default value: 16

wal_keep_segments

Parameter description: Specifies the number of Xlog file segments. Specifies the minimum number of transaction log files stored in the pg_xlog directory. The standby server obtains log files from the primary server for streaming replication.

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

Value range: an integer ranging from 2 to INT_MAX

Default value: 16

Setting suggestions:

• During WAL archiving or recovery from a checkpoint on the server, the system may retain more log files than the number specified by wal_keep_segments.
• If this parameter is set to an excessively small value, a transaction log may have been overwritten by a new transaction before requested by the standby server. As a result, the request fails and the connection between the primary and standby servers is terminated.
• If the HA system uses asynchronous transmission, increase the value of wal_keep_segments when data greater than 4 GB is continuously imported in COPY mode. Take T6000 board as an example. If the data to be imported reaches 50 GB, you are advised to set this parameter to 1000. You can dynamically restore the setting of this parameter after data import is complete and the WAL synchronization is proper.

wal_sender_timeout

Parameter description: Specifies the maximum duration that the sending server waits for the WAL reception in the receiver.

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

NOTICE:

• If the data volume on the primary server is huge, the value of this parameter must be increased for the database rebuilding on a standby server. For example, if the data volume on the primary server reaches 500 GB, you are advised to set this parameter to 600 seconds.
• This parameter cannot be set to a value larger than the value of wal_receiver_timeout or the timeout parameter for database rebuilding.

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

Default value: 6s

max_replication_slots

Parameter description: Specifies the number of log replication slots in the primary server.

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: 8

Setting suggestions:

When using logical replication, you are advised to set this parameter to: Number of current physical replication slots + Number of required logical replication slots.

• Physical replication slots provide an automatic method to ensure that Xlogs are not removed from a primary node before they are received by all the standby nodes and secondary nodes. That is, physical replication slots are used to support primary/standby HA. The number of physical replication slots required by a database is equal to the ratio of standby and secondary nodes to the primary node. For example, if an HA database has 1 primary node, 1 standby node, and 1 secondary node, the number of required physical replication slots will be 2. If an HA database has 1 primary node and 3 standby nodes, the number of required physical replication slots will be 3.
• Plan the number of logical replication slots as follows:
  • A logical replication slot can carry changes of only one database for decoding. If multiple databases are involved, create multiple logical replication slots.
  • If logical replication is needed by multiple target databases, create multiple logical replication slots in the source database. Each logical replication slot corresponds to one logical replication link.

enable_slot_log

Parameter description: Specifies whether to enable primary/standby synchronization for logical replication slots.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on indicates that primary/standby synchronization is enabled for logical replication slots.
• off indicates that primary/standby synchronization is disabled for logical replication slots.

Default value: off

max_changes_in_memory

Parameter description: Specifies the maximum size (bytes) of a single transaction buffered in the memory during logical decoding.

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

Value range: an integer ranging from 1 to 2147483647

Default value: 4096

max_cached_tuplebufs

Parameter description: Specifies the maximum size (bytes) of the total tuple information buffered in the memory during logic decoding. You are advised to set this parameter to a value greater than or equal to twice of max_changes_in_memory.

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

Value range: an integer ranging from 1 to 2147483647

Default value: 8192

replconninfo1

Parameter description: Specifies the information about the first node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the first node is configured.

Default value: empty

replconninfo2

Parameter description: Specifies the information about the second node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the second node is configured.

Default value: empty

replconninfo3

Parameter description: Specifies the information about the third node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the third node is configured.

Default value: empty

replconninfo4

Parameter description: Specifies the information about the fourth node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the fourth node is configured.

Default value: empty

replconninfo5

Parameter description: Specifies the information about the fifth node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the fifth node is configured.

Default value: empty

replconninfo6

Parameter description: Specifies the information about the sixth node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the sixth node is configured.

Default value: empty

replconninfo7

Parameter description: Specifies the information about the seventh node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the seventh node is configured.

Default value: empty

replconninfo8

Parameter description: Specifies the information about the eighth node to be listened to and authenticated by the current server.

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

Value range: a string. An empty string indicates that no information about the eighth node is configured.

Default value: an empty string

available_zone

Parameter description: Specifies the region where the local node is located.

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

Value range: a string. An empty string indicates that no information about the node is configured.

Default value: an empty string