Galera Cluster is a popular solution for high availability and scalability in MySQL or MariaDB database environments. It utilizes a certification-based replication mechanism to ensure data consistency across multiple database nodes. However, in some cases, the default configuration might not deliver optimal performance. In this blog post, we will explore some techniques to optimize Galera certification-based replication for improved performance in a SQL Galera Cluster.

1. Increase the gcache.size

The Galera Cluster uses a global cache (gcache) to store the write-sets that are being replicated between nodes. By default, the size of the gcache is set to a conservative value. Increasing the gcache.size can help improve performance, especially in scenarios with high write-activity.

To increase the size of the gcache, modify the wsrep_provider_options configuration in your my.cnf file:

wsrep_provider_options="gcache.size=<desired_size>"

Replace <desired_size> with the desired size in bytes, for example:

wsrep_provider_options="gcache.size=2G"

2. Fine-tune the Flow Control Mechanism

Flow control is a critical component in Galera Cluster to prevent overloaded nodes from impacting the entire cluster’s performance. By default, Galera uses a flow control mechanism that pauses the replication when a node’s gcache is filled to a certain extent.

To optimize the flow control mechanism, you can adjust the flow_control_min_threshold and flow_control_max_threshold parameters. These parameters define the thresholds at which replication pauses and resumes:

wsrep_provider_options="flow_control_min_threshold=<min_threshold>;flow_control_max_threshold=<max_threshold>"

It is recommended to increase the flow_control_min_threshold and decrease the flow_control_max_threshold to reduce the pause durations and prevent unnecessary replication halts.

Conclusion

Optimizing Galera certification-based replication is essential for achieving better performance in a SQL Galera Cluster. By increasing the gcache.size and fine-tuning the flow control mechanism, you can improve the overall performance and avoid replication bottlenecks.

Remember to always benchmark and test any changes in a non-production environment before applying them to your production cluster.