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.
The biha extension provides a set of configuration parameters described below that are specific to the BiHA cluster.
When setting the cluster configuration parameters, you must ensure network reliability for the changes to affect all cluster nodes without any errors.
It is not recommended to modify any cluster configuration parameters
while one of the nodes is in the NODE_ERROR state,
as the changes may fail to be applied on that node.
biha.autorewind (boolean)
#
An optional parameter that controls the automatic rewind policy
for that node, against which the pg_rewind must be
executed.
For example, for the old leader when synchronizing it with the new leader.
The default value is false meaning that
the automatic rewind is not performed. When the value is set to
true, the automatic rewind is performed after the
error that usually causes the NODE_ERROR state of the
node.
For more information, see Automatic Cluster Synchronization after Failover.
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 is 1000 (1 second).
The value of the biha.callbacks_timeout parameter 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 to false, 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 to false, 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 is on.
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.
Nodes in all states use the heartbeat timeout value calculated as
biha.heartbeat_max_lost *
biha.heartbeat_send_period to determine
if other nodes are online. For example, if Node A receives no heartbeats from Node B
within the heartbeat timeout, the Node B state changes
to UNKNOWN in the biha.status_v
view of Node A indicating that Node A considers Node B offline.
The leader in the LEADER_RW state additionally uses the timeout specified in
the biha.no_wal_on_follower parameter.
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.
Nodes in all states use the heartbeat timeout value calculated as
biha.heartbeat_max_lost *
biha.heartbeat_send_period to determine if other nodes are online.
For example, if Node A receives no heartbeats from Node B
within the heartbeat timeout, the Node B state changes
to UNKNOWN in the biha.status_v
view of Node A indicating that Node A considers Node B offline.
The leader in the LEADER_RW state additionally uses the timeout specified in
the biha.no_wal_on_follower parameter.
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 bihactl init command,
the biha.minnodes value equals the biha.nquorum value.
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,
the minnodes value must be 2.
Nodes with the biha.can_vote parameter set
to false are 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.
BiHA uses this configuration parameter for the following purposes:
When you nominate a follower as the new leader using the biha.set_leader function,
the follower state changes to FOLLOWER_OFFERED. The follower in
this state uses biha.no_wal_on_follower to determine
if it must stop waiting for missing WAL records from the current leader and
can become the new leader.
A follower in the FOLLOWER_OFFERED state checks whether
its WAL location has been updated. Update of WAL location confirms that the
follower keeps receiving replication data from the leader. If the follower
does not receive WAL records longer than
biha.no_wal_on_follower, the follower
state changes to LEADER_RO. In this case,
the log contains the following message: “Timed out waiting for new WAL records from current leader”.
The leader in the LEADER_RW state
uses biha.no_wal_on_follower in conjunction
with the heartbeat timeout value (which is calculated as
biha.heartbeat_max_lost
* biha.heartbeat_send_period)
to determine if other nodes are online.
The leader checks the replication slot positions of
other nodes. If the replication slot position updates, it means that
the node receives replication data from the leader and the node is online.
If the leader does not receive heartbeats from the node within the above mentioned
heartbeat timeout and its replication slot position does not change
within the biha.no_wal_on_follower timeout value,
the leader considers the node offline and its state changes to UNKNOWN
in the biha.status_v view of
the 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.
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 minimum 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,
the nquorum value must be 2.
Nodes with the biha.can_vote parameter set
to false are 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.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.
biha.autowaltrim (boolean)
#
Manages the automatic WAL trimming policy within a single node. When set to
true (default), BiHA automatically
schedules and executes the WAL trimming procedure if possible.
If set to false, the WAL trimming procedure
is not executed and cluster synchronization is performed by means
of pg_rewind.
For more information, see Automatic Cluster Synchronization after Failover.
Configuration parameters listed below relate to the SSL authentication
of the biha_replication_user role. For more information
about SSL authentication configuration,
see Configuring SSL for User Authentication.
biha.user_biha_cert (text)
#
Specifies the path to the SSL public certificate used for the biha_replication_user
role authentication.
biha.user_biha_key (text)
#
Specifies the path to the SSL private key used for the biha_replication_user
role authentication.
biha.ssl_mode (text)
#
Specifies the authentication policy for the biha_replication_user
role. The following modes are supported:
verify-full (default)
require
verify-ca
For more information about modes, see sslmode.
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.BcpTransportSSLDebug_log_level (enum)
#
Specifies the logging level to provide debugging information about the
control channel operation in the SSL mode.
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.
All functions listed below must be called from the biha_db
database, for example:
psql biha_db -c "SELECT biha.set_leader(2)"
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.
Calling the biha.set_leader function on the current
leader is not recommended.
If you call the function on the current
leader in the LEADER_RW state, 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.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.
The following functions are used to change configuration parameters that must have the same values on all cluster nodes. These functions must only be called on the leader node. The changes are applied to all cluster nodes.
You do not need to restart the cluster nodes after calling a function for the changes to take effect unless the function description explicitly specifies otherwise.
biha.set_heartbeat_max_lost (integer) returns boolean
#Sets the biha.heartbeat_max_lost value.
biha.set_heartbeat_send_period (integer) returns boolean
#Sets the biha.heartbeat_send_period value, in milliseconds.
biha.set_no_wal_on_follower (integer) returns boolean
#Sets the biha.no_wal_on_follower value, in milliseconds.
biha.set_minnodes (integer) returns boolean
#Sets the biha.minnodes value.
biha.set_nquorum (integer) returns boolean
#Sets the biha.nquorum value.
biha.set_nquorum_and_minnodes (integer, integer) returns boolean
#Sets the biha.nquorum and biha.minnodes values.
The following functions are used to configure and manage replication.
biha.add_to_ssn (id integer) returns boolean
#You can call this function only when quorum-based synchronous replication is enabled.
Adds a node with the specified ID to the list of synchronous standbys of the synchronous_standby_names parameter. You must specify the node which name is not yet in the list.
biha.get_ssn() returns varchar
#Displays the current value of the synchronous_standby_names parameter.
biha.remove_from_ssn (id integer) returns boolean
#You can call this function only when quorum-based synchronous replication is enabled.
Removes the node with the specified ID from the list of synchronous standbys of the synchronous_standby_names parameter. You must specify the node which name is already in the list.
biha.set_ssn (VARIADIC ids integer) returns boolean
#You can call this function only when quorum-based synchronous replication is enabled.
Sets nodes with the IDs specified in the ids array as the
list of synchronous standbys of the
synchronous_standby_names parameter.
biha.set_sync_standbys (integer) returns boolean
#
Enables quorum-based synchronous replication by setting the
synchronous_standby_names parameter
and specifying the number of synchronous standbys (quorum) with the ANY method.
The value must be positive, higher than the MIN field value of
the synchronous_standby_names parameter if set,
and must not exceed the number of followers excluding referee.
For more information, see
Replication Configuration.
biha.set_sync_standbys_min (integer) returns boolean
#You can call this function only when quorum-based synchronous replication is enabled.
Sets the MIN field value of
the synchronous_standby_names parameter, i.e. the
minimum number of synchronous standbys that must be available for
the leader node to continue operation.
Using this function, you can also manage
relaxed quorum-based synchronous replication.
To disable relaxed quorum-based synchronous replication, set the -1 value.
biha.config () returns setof record
#
Returns the cluster configuration parameter values: id,
term, nquorum,
minnodes, heartbeat_send_period,
heartbeat_max_lost, no_wal_on_follower,
sync_standbys_min, priority,
can_be_leader, can_vote, mode.
biha.error_details () returns setof record
#
Returns the description of why the node transferred to the
NODE_ERROR state. The returned record contains the
type of the error, its details, the place it occurred specifying
begin_lsn, end_lsn, and identifier
of the current and the next timeline, as well as
replay_lsn.
biha.nodes () returns setof record
#
Defines the biha.nodes_v view, which
is described in detail in the biha.nodes_v
section.
biha.status () returns setof record
#
Defines the biha.status_v view, which
is described in detail in the biha.status_v
section. It is not recommended to use this function as it provides
raw data for the view.
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_RW state.
The new callback is replicated to the followers.
On the biha side, there is no check that
func exists in database. If the
specified function does not exist, the callback fails.
See Registering Callbacks for the example of
using the biha.register_callback function.
Table 27.3. Variable Definitions
| Name | Type | Description |
|---|---|---|
event | text | Event of the BiHA cluster that triggers a callback. For more information about events and corresponding callback types, see Callback Types. |
func | text |
Name of the SQL function that biha executes
when event happens. This function
must be located in database, otherwise it
cannot be executed.
|
database | text | Database where func is executed.
|
executor | text |
User that executes |
priority | integer |
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_RW state.
See Unregistering Callbacks for the example of
using the biha.unregister_callback function.
biha.get_magic_string () returns string
#Generates a magic string for the cluster node.
biha.reset_node_error () returns boolean
#
Resets the NODE_ERROR state on a node. Use this
function after you fix the issue that caused the NODE_ERROR state.
For more information, see Restoring the Node from the NODE_ERROR State.
To query the views listed below, you must first connect to
the biha_db database.
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. |
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. The data type is integer.
|
online |
Shows whether the node is online. The data type is
boolean
(t or f).
|
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. The data type is
interval.
|