Strong Consistency

CockroachDB replicates your data multiple times and guarantees consistency between replicas.

Key properties:

• CockroachDB guarantees serializable SQL transactionsas long as system clocks are synchronized with NTP
• No downtime for server restarts, machine failures, or datacenter outages
• Local or wide-area replication with no stale reads on failover

• Employs Raft, a popular successor to Paxos
  How does this work?

• Stored data is versioned with MVCC, so reads simply limittheir scope to the data visible at the time the read transaction started.

• Writes are serviced using theRaft consensus algorithm, a popularalternative toPaxos.A consensus algorithm guarantees that any majority of replicastogether always agree on whether an update was committedsuccessfully. Updates (writes) must reach a majority of replicas (2out of 3 by default) before they are considered committed.

To ensure that a write transaction does not interfere with read transactions that start after it, CockroachDB also uses a timestamp cache which remembers when data was last read by ongoing transactions.

This ensures that clients always observe serializable consistency with regards to other concurrent transactions.

See also

• Serializable, Lockless, Distributed: Isolation in CockroachDB
• Consensus, Made Thrive
• Trust, But Verify: How CockroachDB Checks Replication
• Living Without Atomic Clocks
• The CockroachDB Architecture Document

Was this page helpful?
YesNo