After Discord reached roughly a trillion stored messages, it migrated its main message database from Apache Cassandra to ScyllaDB. Discord completed the message-store switch in May 2022.
The move followed an earlier transition from MongoDB to Cassandra. Cassandra initially offered the distributed, fault-tolerant storage Discord needed, but the message cluster eventually grew to 177 nodes and accumulated trillions of messages. Operators faced unpredictable latency, difficult repairs, and increasing maintenance work.
ScyllaDB was attractive because it is Cassandra-compatible while using a C++ architecture without Java’s garbage collector. Discord reported that its migration reduced the large message cluster from 177 Cassandra nodes to 72 ScyllaDB nodes. Historical-message read latency improved from a Cassandra p99 range of 40–125 milliseconds to about 15 milliseconds, while message inserts settled near a 5-millisecond p99.
The wording can cause confusion because Discord did not jump directly from MongoDB to ScyllaDB. Its broad database path was MongoDB, then Cassandra, then ScyllaDB; the trillion-message milestone refers to the final transition.