All You Need to Know About GCache (Galera-Cache)mariadb, mysql, percona
This blog discusses some important aspects of GCache.
Why do we need GCache?
Percona XtraDB Cluster is a multi-master topology, where a transaction executed on one node is replicated on another node(s) of the cluster. This transaction is then copied over from the group channel to Galera-Cache followed by apply action.
The cache can be discarded immediately once the transaction is applied, but retaining it can help promote a node as a DONOR node serving write-sets for a newly booted node.
So in short, GCache acts as a temporary storage for replicated transactions.