Yugabyte Query Layer (YQL)
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The YQL layer implements the server-side of multiple protocols/APIs that YugabyteDB supports. Currently, YugabyteDB supports YCQL and YEDIS, 2 transactional NoSQL APIs, and YSQL, a distributed SQL API. The 2 NoSQL APIs are wire compatible with Cassandra Query Language (CQL) and Redis while the SQL API is wire compatible with PostgreSQL.
Every YB-TServer is configured to support these protocols, on different ports. Port 9042 is the default port for CQL-compatible protocol and 6379 is the default port used for the Redis-compatible protocol. Port 5433 is used for the PostgreSQL-compatible protocol.
From the application perspective this is a stateless layer and the clients can connect to any (one or more) of the YB-TServers on the appropriate port to perform operations against the YugabyteDB cluster.
The YQL layer running inside each YB-TServer implements some of the API specific aspects of each support API (such as YCQL or YEDIS or YSQL), but ultimately replicates/stores/retrieves/replicates data using DocDB, YugabyteDB’s common underlying strongly-consistent & distributed store. Some of the sub-components in YQL are:
- A CQL compiler and execution layer - This component includes a “statement cache”, a cache for compiled/execution plan for prepared statements to avoid overheads associated with repeated parsing of CQL statements.
- A Redis command parser and execution layer
- Support for language specific builtin operations, data type encodings, etc.