Storage Model

Custom

CockroachDB stores its data in the distributed key-value store.

Joins

Hash Join

There are two ways of join in CockroachDB, join-by-lookup and stream joins. Join-by-lookup iterate through one table and lookup for it in the other table. Stream joins is an execution plan based on hashing.

Data Model

Relational

Concurrency Control

Multi-version Concurrency Control (MVCC)

Transactions in CockroachDB is implemented

Isolation Levels

Serializable Snapshot Isolation

CockroachDB supports snapshot isolation (SI) and serializable snapshot isolation (SSI). It is implemented using RocksDB snapshot capability.

System Architecture

Shared-Nothing

CockroachDB has two layers, the SQL layer and the storage layer. The SQL layer sits on top of the transactional and strongly-consistent distributed key-value store. In the key-value store, the key ranges are divided and stored in RocksDB and replicated across cluster. It exports structured data API of relational concepts. It exports standard SQL interface at the SQL layer. The SQL layer translates SQL statements into calls to structured data API.

Logging

Physical Logging

Query Compilation

Not Supported

Stored Procedures

Not Supported

Query Interface

SQL

CockroachDB aims to provide standard SQL with extensions, but some standard SQL functionality is under development.

Indexes

B+Tree

CockroachDB supports primary key and secondary key indexes using B+Trees. The indexes are implemented with the distributed key-value store ranges.

Views

Not Supported

Query Execution

Tuple-at-a-Time Model

The query execution is similar to stream processing. When executing a query, the execution plan is transformed into a DAG, a gateway node orchestrates participating nodes begin processing.

Storage Architecture

Disk-oriented

The backend storage in CockroachDB is RocksDB. It is disk-oriented storage.