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How are state transfers done in Galera Cluster?
The process of replicating data from the cluster to the individual node, bringing the node into sync with the cluster, is known as provisioning. There are two methods available in Galera Cluster to provision nodes: State Snapshot Transfers (SST) Where a snapshot of the entire node state transfers.
How does a state snapshot transfer ( SST ) work?
In a State Snapshot Transfer (SST), the cluster provisions nodes by transferring a full data copy from one node to another. When a new node joins the cluster, the new node initiates a State Snapshot Transfer to synchronize its data with a node that is already part of the cluster.
Which is faster SST or IST in Galera?
IST is a method to prepare a joiner by sending only the missing writesets available in the donor’s gcache. gcache is a file where a Galera node keeps a copy of writesets. IST is faster than SST, it is non-blocking and has no significant performance impact on the donor. It should be the preferred option whenever possible.
What is port for multicast replication in Galera?
Galera Replication Port (default: 4567) – For Galera Cluster replication traffic, multicast replication uses both UDP transport and TCP on this port. Can be changed by setting wsrep_node_address . IST Port (default: 4568) – For Incremental State Transfers.
How does Galera Cluster add a new node?
Galera Cluster has the ability to add new nodes to the cluster by handling internally the transfer of the entire dataset to the new node. The same procedure, called State Snapshot Transfer (SST), applies to nodes that are rejoining the cluster after being down for a longer period of time.
How does a new node join a cluster?
When a new node joins a cluster, it will try to synchronize with the cluster by getting a full copy of the databases from one of the other nodes. This is known as a State Transfer. It will use a tool like rsync or mysqldump, depending on how the wsrep_sst_method option was set.
Which is the slowest state transfer in Galera?
The Donor Node becomes READ-ONLY for the duration of the transfer. The State Snapshot Transfer applies the FLUSH TABLES WITH READ LOCK command on the donor node. mysqldump is the slowest method for State Snapshot Transfers. This can be an issue in a loaded cluster.