Delving into Galera Cluster Status with MariaDB

• Permissions
  

  • Due to the sensitive nature of cluster information, SHOW WSREP_STATUS requires the SUPER privilege to execute.
  • This ensures only authorized users can access this critical data.

• Implementation
  

  • SHOW WSREP_STATUS doesn't directly interact with the database tables.
  • Instead, it retrieves data from internal structures maintained by Galera for cluster management.
  • This information is then formatted and presented as a result set similar to a traditional SQL query.
• • SHOW WSREP_STATUS retrieves information about the Galera cluster node and its overall health. This includes details like:
    • Node status (online/offline)
    • Replication status (synced/partitioned)
    • Cluster communication details
  • It essentially acts like a system query for the Galera layer.

Alternatives
* While SHOW WSREP_STATUS provides a quick overview, for some purposes, you might consider: * The information_schema.WSREP_STATUS table: This table stores the same information as the SHOW statement and can be queried with appropriate privileges (less than SUPER).

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This example shows how to use the SHOW WSREP_STATUS statement:

SHOW WSREP_STATUS;

This will output a table containing information about the Galera cluster node and its status. The specific columns and their values will depend on your cluster configuration.

Using information_schema.WSREP_STATUS table

This example shows how to query the information_schema.WSREP_STATUS table:

SELECT * FROM information_schema.WSREP_STATUS;

This will also output a table with the same information as SHOW WSREP_STATUS.

Filtering information_schema.WSREP_STATUS

You can filter the information retrieved from the information_schema.WSREP_STATUS table using a WHERE clause. For example, to get the status of a specific node (assuming Node_Index is used for identification):

SELECT * FROM information_schema.WSREP_STATUS WHERE Node_Index = 1;

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1. Information Schema Table (information_schema.WSREP_STATUS)

This is the most direct alternative. As mentioned earlier, this table stores the same information as retrieved by the SHOW WSREP_STATUS statement. You can query this table with SELECT statements and even filter results using the WHERE clause (potentially with lower privileges than SUPER).

1. Status Variables

Galera exposes various status variables that provide detailed information about different aspects of the cluster. You can access these variables using functions like @@global.variable_name or by querying the performance_schema.replication_status table. This approach offers more granular control over the specific data you want to retrieve.

1. Galera logs

For in-depth troubleshooting or analyzing historical behavior, Galera logs can be valuable. These logs typically reside in a dedicated directory on your server and contain detailed information about cluster communication, errors, and events.

Method	Description	Advantages	Disadvantages
SHOW WSREP_STATUS	Statement for cluster health overview	Simple and quick	Requires SUPER privilege
information_schema.WSREP_STATUS	Table containing cluster information	More control over data access (potentially lower privilege)	Same information as SHOW statement
Status Variables	Access specific cluster aspects	Highly granular control over retrieved data	Requires knowledge of specific variable names
Galera logs	Detailed historical information	Valuable for troubleshooting	Requires parsing logs, might be overwhelming for basic checks