In a SQL Galera Cluster, the WebSockets Replication (WSREP) API is a powerful tool for advanced cluster management. It provides a way to programmatically interact with the cluster and perform actions such as node control, cluster monitoring, and application integration.
The WSREP API allows you to automate certain tasks and gather important information about the state of the cluster. In this blog post, we will explore some of the key use cases and features of the WSREP API.
Cluster monitoring
Monitoring the health and status of a Galera Cluster is crucial for ensuring its stability and performance. The WSREP API provides several methods for collecting information about the cluster’s current state, such as node status, cluster size, and replication lag.
import mysql.connector
# Connect to a node in the Galera Cluster
cnx = mysql.connector.connect(user='user', password='password', host='node1')
# Retrieve the cluster size
cursor = cnx.cursor()
cursor.execute("SELECT wsrep_cluster_size()")
cluster_size = cursor.fetchone()[0]
cursor.close()
print(f"Cluster size: {cluster_size}")
# Retrieve the replication lag
cursor = cnx.cursor()
cursor.execute("SELECT wsrep_evs_state()")
replication_state = cursor.fetchone()[0]
cursor.close()
print(f"Replication lag: {replication_state}")
Node control
The WSREP API allows you to control the behavior and status of individual nodes within the cluster. You can start, stop, or evict nodes programmatically, providing flexibility in managing the cluster topology.
import mysql.connector
# Connect to a node in the Galera Cluster
cnx = mysql.connector.connect(user='user', password='password', host='node1')
# Stop a node
cursor = cnx.cursor()
cursor.execute("SET GLOBAL wsrep_desync=ON")
cursor.close()
# Start a node
cursor = cnx.cursor()
cursor.execute("SET GLOBAL wsrep_desync=OFF")
cursor.close()
# Evict a node
cursor = cnx.cursor()
cursor.execute("SET GLOBAL wsrep_sst_donor_rejects_queries = ON")
cursor.close()
Application integration
Integrating your application with the WSREP API allows you to react to cluster events and take appropriate actions. You can listen for cluster membership changes, node failure or recovery events, and other important events.
import mysql.connector
from mysql.connector import MySQLConnection, pooling
# Define a callback function to handle cluster events
def handle_event(event):
print(f"Cluster event: {event}")
# Create a connection pool
pool = mysql.connector.pooling.MySQLConnectionPool(
pool_name="wsrep_pool",
pool_size=5,
user='user',
password='password',
host='node1',
database='database',
autocommit=True
)
# Create a connection and register the callback function
cnx = pool.get_connection()
wsrep_cnx = MySQLConnection(
user='user',
password='password',
host='node1',
database='database',
autocommit=True,
wsrep_notify_cb=handle_event
)
cnx._reset_cnx(wsrep_cnx)
cnx._consume_events()
Conclusion
The WSREP API in SQL Galera Cluster offers advanced cluster management capabilities, enabling you to monitor the cluster, control individual nodes, and integrate your application with cluster events. By leveraging the WSREP API, you can automate and streamline cluster management tasks to ensure the stability and performance of your Galera Cluster.
#galera #clustermanagement