A YugabyteDB universe is a group of nodes (VMs, physical machines, or containers) that collectively function as a highly available and resilient database.
NoteIn most of the docs, the term
universeare used interchangeably. However, the two are not always equivalent. The difference is described in a section below.
The universe can be deployed in a variety of configurations depending on business requirements, and latency considerations. Some examples:
- Single availability zone (AZ/rack/failure domain)
- Multiple AZs in a region
- Multiple regions (with synchronous and asynchronous replication choices)
Organization of user data
A YugabyteDB universe can consist of one or more namespaces. Each of these namespaces can contain one or more user tables.
YugabyteDB automatically shards, replicates and load-balances these tables across the nodes in the universe, while respecting user-intent such as cross-AZ or region placement requirements, desired replication factor, and so on. YugabyteDB automatically handles failures (e.g., node, process, AZ or region failures), and re-distributes and re-replicates data back to desired levels across the remaining available nodes while still respecting any data placement requirements.
Namespaces in YSQL are referred to as databases and are logically the same as in other RDBMS databases (such as PostgreSQL).
A namespace in YCQL is referred to as a keyspace and is logically the same as a keyspace in Apache Cassandra's CQL.
Processes and services
A universe comprises of two sets of processes, YB-TServer and YB-Master. The YB-TServer and YB-Master processes form two respective distributed services using Raft as a building block. High availability (HA) of both these services is achieved by the failure-detection, leader election and data replication mechanisms in the Raft implementation.
NoteYugabyteDB is architected to not have any single point of failure.
These serve different purposes as described below.
The YB-TServer (aka the YugabyteDB Tablet Server) processes are responsible for hosting/serving user data (for example, tables). They deal with all the user queries.
For details, see YB-TServer .
The YB-Master (aka the YugabyteDB Master Server) processes are responsible for keeping system metadata, coordinating system-wide operations, such as create/alter/drop tables, and initiating maintenance operations such as load balancing.
For details, see YB-TServer .
Below is an illustration of a simple 4-node YugabyteDB universe:
Universe vs cluster
A YugabyteDB universe can comprise of one or more clusters. Each cluster is a logical group of nodes running YB-TServer services that are performing one of the following replication modes:
- Synchronous replication
- Asynchronous replication
The set of nodes that are performing strong replication are referred to as the primary cluster and other groups are called read replica clusters.
- There is always one primary cluster in a universe.
- There can be zero or more read replica clusters in that universe.
For more information about read replica clusters, see read replicas .