27.4. Reference for the biha Extension #
biha is a Postgres Pro extension that allows managing a BiHA cluster.
This section contains information about the biha extension configuration parameters, functions, and views.
27.4.1. Configuration Parameters #
The biha extension provides a set of configuration parameters described below that are specific to the BiHA cluster.
27.4.1.1. Cluster Configuration #
Important
When setting the cluster configuration parameters, you must ensure network reliability for the changes to affect all cluster nodes without any errors.
biha.autorewind(boolean) #An optional parameter that controls the automatic rewind policy for that node, against which the
pg_rewindmust be executed. For example, for the old leader when synchronizing it with the new leader. The default value isfalsemeaning that the automatic rewind is not performed. When the value is set totrue, the automatic rewind is performed after the error that usually causes theNODE_ERRORstate of the node. The automatic rewind is performed if it may complete successfully meaning that preliminary launching of pg_rewind with the--dry-runoption was a success. If the automatic rewind fails, the node is transferred to theNODE_ERRORstate. In this case, you can find the actual rewind state of the node in thebiha.statefile as described in Section 27.3.7. Note that the rewind may cause the loss of some node WAL records.biha.callbacks_timeout(integer) #Sets time for execution of all callbacks for a single event, in milliseconds. The default value is
10000(10 seconds). The minimum value is1000(1 second).The value of the
biha.callbacks_timeoutparameter can be different for different nodes. Changing the value for the leader does not change it for the followers.biha.can_be_leader(boolean) #Determines the ability of a node to become the leader. The default value is
true. If set tofalse, the node cannot stand as a candidate in elections of the new leader.A node that cannot become the leader may have the largest WAL. In this case, if elections are required, those nodes that can stand as candidates attempt to receive missing data from that node. If they succeed, one of these nodes becomes the leader. If they fail to receive missing data, the automatic rewind process is launched on the node that cannot become the leader. If biha.autorewind is not enabled, the node state changes to
NODE_ERROR.biha.can_vote(boolean) #Determines whether a node is allowed to vote. The default value is
true. If set tofalse, the node cannot vote, as well as cannot stand as a candidate in elections of the new leader.biha.flw_ro(boolean) #Determines whether a follower is available for read operations. If set to
off, reading from this follower is prohibited. The default value ison.biha.heartbeat_max_lost(integer) #Specifies the maximum number of heartbeats that can be missed before the node is considered offline. This parameter can be set with the biha.set_heartbeat_max_lost function. The default value is
10.biha.heartbeat_send_period(integer) #Specifies the heartbeat sending frequency, in milliseconds. This parameter can be set with the biha.set_heartbeat_send_period function. The default value is
1000.biha.host(text) #Specifies the host of the cluster node. It is not recommended to modify this parameter.
biha.id(integer) #Specifies the ID of the high-availability cluster node. This parameter is unique for each node of the cluster. It is not recommended to modify this parameter.
biha.minnodes(integer) #Specifies the minimum number of operational nodes for the leader node to be open for write transactions. This parameter can be set with the biha.set_minnodes function. If you do not specify the --minnodes option in
bihactlinit command, thebiha.minnodesvalue equals thebiha.nquorumvalue.When setting up this value, consider the split-brain risk. It is recommended to use the following formula: (
total number of nodes+ 1)/2. For example, if your cluster has 3 nodes, theminnodesvalue must be 2.Nodes with the biha.can_vote parameter set to
falseare ignored.biha.no_wal_on_follower(integer) #Specifies the timeout of the replication slot position advancement, in milliseconds. This parameter can be set with the biha.set_no_wal_on_follower function. The default value is
20000.The leader in
LEADER_RWorLEADER_ROstates stores the time of the replication slot position change on all cluster nodes. If the replication slot position of a node has not changed for the time specified in thebiha.no_wal_on_followerparameter and the heartbeat timeout value (which is calculated as biha.heartbeat_max_lost * biha.heartbeat_send_period) is exceeded, the leader in theLEADER_RWstate changes the state toUNKNOWNin the biha.status_v view. The leader in theLEADER_ROstate only considers the heartbeat timeout value and similarly changes the node state toUNKNOWN.If you switch the leader manually using the biha.set_leader function, the node in the
FOLLOWER_OFFEREDstate checks itsbiha.no_wal_on_followervalue. If the node in theFOLLOWER_OFFEREDstate determines that it has not received any new replication data from the old leader during time specified inbiha.no_wal_on_follower, the node state changes toLEADER_RO. In this case, the log contains the following message: “Timed out waiting for new WAL records from current leader”.biha.node_priority(integer) #Sets the node priority in a cluster with synchronous replication, in seconds. The value determines the timeout that must be reached before the node stands as a candidate in elections. The zero value indicates the highest priority. The default value is
-1, meaning that the parameter is ignored.Important
To ensure correct operation of this parameter, set the --sync-standbys value one unit less than the total number of cluster nodes.
biha.nquorum(integer) #Specifies the number of nodes, which must vote for the new leader node if the current leader is down. This parameter can be set with the biha.set_nquorum function.
When setting up this value, consider the split-brain risk. It is recommended to use the following formula: (
total number of nodes+ 1)/2. For example, if your cluster has 3 nodes, theminnodesvalue must be 2.Nodes with the biha.can_vote parameter set to
falseare ignored.biha.port(integer) #Specifies the port used to exchange service information between nodes. This parameter is required to establish a connection with the cluster. It is not recommended to modify this parameter.
biha.sync_standbys_min(integer) #Specifies the minimum number of synchronous follower nodes that must be available for the leader node to continue operation. This parameter can be set with the biha.set_sync_standbys_min function. The value must be lower than --sync-standbys and cannot be negative. The default value is
-1, meaning that the parameter is ignored. If the parameter is not specified, the BiHA cluster operates according to the default synchronous replication restrictions, i.e., the leader node is not available for write transactions until all followers catch up with its current state.Note
Both the
biha.sync_standbys_minparameter and the biha.set_sync_standbys_min function can operate only if you set the --sync-standbys-min option when initializing the BiHA cluster by means of thebihactlinit command.biha.use_ssl(boolean) #Specifies whether to use the protected mode of the service information exchange between cluster nodes with SSL/TLS over the biha control channel. It is not recommended to modify this parameter.
27.4.1.2. biha Logging Levels #
biha.BihaLog_log_level(enum) #Specifies the logging level to provide general information about the operation of biha components. The default value is
LOG.biha.BcpTransportDebug_log_level(enum) #Specifies the logging level to provide debugging information about the control channel operation. The default value is
DEBUG4.biha.BcpTransportDetails_log_level(enum) #Specifies the logging level to provide detailed information about the control channel operation. The default value is
DEBUG4.biha.BcpTransportLog_log_level(enum) #Specifies the logging level to provide general information about the control channel operation. The default value is
DEBUG4.biha.BcpTransportWarn_log_level(enum) #Specifies the logging level to provide warnings of likely problems in the control channel. The default value is
DEBUG4.biha.NodeControllerDebug_log_level(enum) #Specifies the logging level to provide debugging information about the node controller operation. The default value is
DEBUG4.biha.NodeControllerDetails_log_level(enum) #Specifies the logging level to provide detailed information about the node controller operation. The default value is
DEBUG4.biha.NodeControllerLog_log_level(enum) #Specifies the logging level to provide general information about the node controller operation. The default value is
DEBUG4.biha.NodeControllerWarn_log_level(enum) #Specifies the logging level to provide warnings of likely problems in the node controller. The default value is
DEBUG4.
27.4.2. Functions #
All functions listed below should be called from the biha_db database, for example:
psql biha_db -c "select biha.set_leader(2)"
27.4.2.1. Cluster Configuration #
biha.config () returns setof record#Returns the cluster configuration values:
id,term,nquorum,minnodes,heartbeat_send_period,heartbeat_max_lost,no_wal_on_follower,sync_standbys_min,priority,can_be_leader,can_vote.biha.get_magic_string () returns string#Generates a magic string for the cluster node.
biha.reset_node_error () returns boolean#Resets the
NODE_ERRORstate on a node. Use this function after you fix the issue that caused theNODE_ERRORstate.biha.set_heartbeat_max_lost (integer) returns boolean#Sets the biha.heartbeat_max_lost value. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_heartbeat_send_period (integer) returns boolean#Sets the biha.heartbeat_send_period value, in milliseconds. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_leader (id integer) returns boolean#Sets the leader node manually. It is recommended to call this function on the node that you want to set as the new leader.
Note
Calling the
biha.set_leaderfunction on the current leader is not recommended. If you call the function on the current leader in theLEADER_RWstate, in case of a successful switchover request, there may not be enough time for the request result to be sent to the client before the current leader reboots for demotion.biha.set_no_wal_on_follower (integer) returns boolean#Sets the biha.no_wal_on_follower value, in milliseconds. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_minnodes (integer) returns boolean#Sets the biha.minnodes value. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_nquorum (integer) returns boolean#Sets the biha.nquorum value. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_nquorum_and_minnodes (integer, integer) returns boolean#Sets the biha.nquorum and biha.minnodes values. This function can be called only from the leader node and changes the parameters on all nodes. You do not need to restart the cluster for the changes to take effect.
biha.set_sync_standbys_min (integer) returns boolean#Sets the biha.sync_standbys_min value and changes the
MINfield value of the synchronous_standby_names parameter accordingly if required. This function can be called only from the leader node and changes the parameter on all nodes. You do not need to restart the cluster for the changes to take effect.Note
Both the biha.sync_standbys_min parameter and the
biha.set_sync_standbys_minfunction can operate only if you set the biha.set_sync_standbys_min option when initializing the BiHA cluster by means of thebihactlinit command.biha.remove_node (id integer) returns boolean#Removes the node from the cluster. Before removing, the node must be stopped. This function can only be called on the leader node.
27.4.2.2. Cluster Monitoring #
biha.error_details () returns setof record#Returns the description of why the node transferred to the
NODE_ERRORstate. The returned record contains the type of the error, its details, the place it occurred specifyingbegin_lsn,end_lsn, and identifier of the current and the next timeline, as well asreplay_lsn.biha.nodes () returns setof record#Defines the
biha.nodes_vview, which is described in detail in the biha.nodes_v section.biha.status () returns setof record#Defines the
biha.status_vview, which is described in detail in the biha.status_v section. If the node does not respond when trying to display the view, try the same request on any other node to learn the actual state of cluster nodes.
27.4.2.3. Callback Management #
biha.register_callback (event text, func text, database text, executor text, priority integer) returns integer#Adds a new callback and returns its unique ID. This function can only be called from the leader node in the
LEADER_RWstate. The new callback will be replicated to the followers.Note
On the biha side, there is no check that
funcexists indatabase. If the specified function does not exist, the callback fails.See Registering Callbacks for the example of using the
biha.register_callbackfunction.Table 27.3. Variable Definitions
Name Type Description eventtext Event of the BiHA cluster that triggers a callback. For more information about events and corresponding callback types, see Callback Types. functext Name of the SQL function that biha executes when eventhappens. This function must be located indatabase, otherwise it cannot be executed.databasetext Database where funcis executed.executortext User that executes
func. This parameter is optional. The default value isbiha_callbacks_user.priorityinteger The lower the value, the sooner the callback is executed. This parameter is optional. The default value is 0.biha.unregister_callback(callback_id)#Deletes a callback. This function can only be called on the leader node in the
LEADER_RWstate. See Unregistering Callbacks for the example of using thebiha.unregister_callbackfunction.
27.4.3. Views #
To query the views listed below, you must first connect to the biha_db database.
27.4.3.1. biha.nodes_v #
This view displays the connection status of nodes in the cluster. For the node that the view is queried on, the following columns contain NULL: state, since_conn_start, conn_count.
Table 27.4. The biha.nodes_v view
| Column Name | Description |
|---|---|
id | The node ID. |
host | The host of the node. |
port | The port of the node. |
state | The connection state of the node. This column may contain one of the following values: ACTIVE, CONNECTING, IDLE, or INIT. |
since_conn_start | The time since the node connection. |
conn_count | The number of times the node was connected since the start of the cluster. |
27.4.3.2. biha.status_v #
This view displays the state of nodes in the cluster.
Table 27.5. The biha.status_v View
| Column Name | Description |
|---|---|
id | The node ID. |
leader_id | The leader node ID. |
term | The term of the node. This is used for the purposes of the leader election. |
online | Shows whether the node is online. |
state | The state of the node. This column may contain one of the following values:
|
last_known_state | The last known state of the node. |
since_last_hb | The time since the last received heartbeat message. |