Updated April 19, 2023
Introduction to MariaDB Cluster
MariaDB cluster to build multi master replication with the help of MariaDB Server. Galera is dependent on a virtual replication method and it ensures that whatever data we apply to the other node before it is committed. If all nodes have the same data that means node failure is avoided and no data is lost. If any node fails during the execution then we can easily recover that loss and make it up to data with the help of MariaDB cluster that means it is a high availability solution and it is helpful for organization to maintain a high availability solution.
Syntax:
galera_new_cluster mariadb@ name of clusterExplanation:
- In above syntax we use galera_new_cluster option with mariadb as shown in above syntax, in which we use the name of cluster option for new cluster name with localhost name.
How to Perform Clustering in MariaDB?
Basically the Galera cluster is supported by MariaDB Server, so let’s see how it can perform in MariaDB as follows.
Basically MySQL –wsrep patch is used for MariaDB Server and it is one type of library that we need to add before use of the cluster. For implementation purposes we need to install the standard version of MariaDB Server and Galera wsrep library packages. MariaDB 10.1 and above version and MySQL wsrep patch are merged into the MarisDB Server. That means we can use Galera clustering after installation of MariaDB Server packages and Galera wsrep library packages.
- Swap size requirement: Normal operation of MariaDB Galera node does not consume more memory as compared to the regular MariaDB Server. But at the same time when we execute a certification index and uncommitted write set then it consumes more memory.
- Writeset caching during state transfer: When any node receives a request for a state transfer but at that time it cannot process an incoming writeset request because there is no state available for that request. In this case nodes send state transfer but it is not possible to apply writeset due to the dependent nature of state transfer mechanism. In the current version writeset are cached into the memory and if the system runs out of memory then state transfer fails or the cluster will block and wait for state transfer to end.
Installation of MariaDB Galera Cluster
For use of MariaDB Galera Cluster we required different packages as follows:
- First required supported version of MariaDB Server and second package is that Galera wsrep provider library.
- Installation of MariaDB Galera cluster is the same as MariaDB Server packages, however we also need to install some additional packages that are Galera wsrep provider library. Basically MariaDB Galera Clustering is supported by the Linux operating system.
- So we can install MariaDB Galera Cluster by using different commands on the LINUX terminal, some packages installation we use yum/dnf command and some packages we need apt-get command.
How we can Configure MariaDB Galera Cluster?
We need to set different option for MariaDB Galera Cluster.
1. Bootstrapping a New Cluster
When we create new node at that time cluster needs to be bootstrapped by using mysqld with –wsrep-new-cluster option. This option is helpful to recognize that no existing cluster is available to connect, at that time a newly created node creates a new UUID number to identify the newly created cluster. When a newly created cluster is connected to an existing cluster then there is no need to use –wsrep-new-cluster option. in this case we just restart the newly created node then it creates a new UUID to identify the cluster again and node not connected to the old cluster.
2. Systemd and Bootstrapping
In this option we use the system option for the operating system. In this option we can create a new cluster by using MariaDB Galera Cluster.
3. SysVinit and Bootstrapping
This is another option to set the MariaDB Galera Cluster.
4. Adding Another Node to the Cluster
Suppose our cluster is in running state and if we want to add or reconnect another node at that time we must need an address of another cluster and this address passes to the MariaDB Server with –wsrep -new-cluster option.
5. Restarting the Cluster
Sometimes what happens at the same time we shut down all nodes that means we terminated all clusters. In this case cluster data still exists but running of cluster no longer exists. When this situation occurs we must need to bootstrap the cluster again. If the terminated cluster is not bootstrap and mysqld is started first node normally then nodes will try to connect the cluster.
Example
Given below is the example of MariaDB Cluster:
Code:
SHOW GLOBAL STATUS LIKE 'wsrep_%';Explanation:
- With the help of a database client we can check the status of write-set replication by using above standard query.
- Currently we don’t have any cluster or node but when we execute the above query then it shows the result as an empty set.
- The final output of the above query we illustrate by using the following snapshot.
Output:
Suppose we need to check the integrity of the cluster. At that time we can use the following statement as follows.
Code:
SHOW GLOBAL STATUS LIKE 'wsrep_cluster_state_uuid';Explanation:
- In the above example we use show global status command with a clause with ‘wsrep_cluster_state_uuid’ this parameter is used to show the UUID number of the cluster.
- Every node in the cluster must have the same value. When a node has different values that means the node is no longer connected to the cluster.
- The final output of the above query we illustrate by using the following snapshot.
Output:
Code:
SHOW GLOBAL STATUS LIKE 'wsrep_cluster_status';Explanation:
- With the help of the above statement we primary status of the created cluster.
- Basically we can create clusters on Centos or Linux, with the help of above syntax. Similarly we use different commands with show global status keyword to see the cluster status during the execution.
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