Your database has a minimum number of nodes that must be up and part of the database cluster for the database to continue operating. When this minimum requirement is met, your database has a quorum of nodes.

The number of nodes that make up a quorum depends on the database mode:

  • In Enterprise Mode, over half the nodes (50% of total nodes + 1) must be up.
  • In Eon Mode, over half of the primary nodes in the cluster must be up.

The database can lose quorum if too many nodes go down. The database's reaction to losing quorum also depends on the database's mode:

  • An Enterprise Mode database that loses quorum shuts down to prevent potential data corruption.
  • An Eon Mode database that loses quorum goes into read-only mode to prevent potential data corruption. In this mode, you can usually execute queries, but DDL and DML statements fail with an error.

For more on database availability, see K-Safety in an Enterprise Mode Database and Data Integrity and High Availability in an Eon Mode Database.