Before you start using CockroachDB, you should understand a couple important mechanics of the database:
- How transactions work in CockroachDB
- How applications interact with CockroachDB
Note that the sections that follow were written for the purposes of orienting application developers. For more detailed technical documentation on CockroachDB's architecture, see our architecture documentation.
How transactions work in CockroachDB
CockroachDB is designed to make your data scalable and consistent. All stored records are replicated across a distributed deployment of database instances, and all database transactions committed in CockroachDB satisfy ACID properties and the CAP theorem. This means that when you store data in CockroachDB, the data will be valid and anomaly-free, even in the event of a system error or power failure.
To guarantee that database operations are atomic (the "A" of the ACID properties), CockroachDB executes all statements in the context of an atomic database transaction. If a transaction succeeds, all data mutations are applied together simultaneously from the perspective of operations outside of the transaction. If any part of a transaction fails, the entire transaction is aborted, and the database is left unchanged.
Managing transactions is an important part of CockroachDB application development. When creating your application's persistence layer, you must understand how CockroachDB interacts with your application framework's transaction management system. You should also have some knowledge of CockroachDB's transaction syntax. We go into more detail about transaction management in Manage Transactions.
Serializability and transaction contention
SERIALIZABLE transaction isolation (the "I" of ACID semantics). If transactions are executed concurrently, the final state of the database will appear as if the transactions were executed serially.
SERIALIZABLE isolation, the strictest level of isolation, provides the highest level of data consistency and protects against concurrency-based attacks and bugs.
SERIALIZABLE isolation, CockroachDB locks the data targeted by an open transaction. If a separate transaction attempts to modify data that are locked by an open transaction, the newest transaction will not succeed, as committing it could result in a violation of the
SERIALIZABLE isolation level. This scenario is called transaction contention, and should be avoided when possible. For a more detailed explanation of transaction contention, and tips on how to avoid it, see Understand and Avoid Transaction Contention.
In some cases, transaction contention is unavoidable. If a transaction fails due to contention, CockroachDB will automatically retry the transaction, or will return a transaction retry error to the client. Most official CockroachDB client libraries include a transaction-retrying wrapper function to make writing your persistence layer easier. If your framework's client library does not include a retry wrapper, you will need to write transaction retry logic in your application. We go into more detail about transaction retries later in the guide, in Retry Transactions.
How applications interact with CockroachDB
CockroachDB supports the PostgreSQL wire protocol, and CockroachDB supports most PostgreSQL syntax and features, making most PostgreSQL client libraries compatible with CockroachDB. Cockroach Labs also maintains official CockroachDB adapters for some of the most popular PostgreSQL drivers and ORMs. Using an official CockroachDB adapter can help simplify transaction management and performance optimization in your application. If an official CockroachDB adapter does not yet exist for your application's data framework, we recommend just using the PostgreSQL client library that works for your application.
A growing number of popular third-party database tools offer full support for CockroachDB. Because CockroachDB uses the PostgreSQL wire protocol and supports PostgreSQL syntax, most PostgreSQL-compatible third-party tools are also compatible with CockroachDB. For a list of libraries and tools that we have tested against CockroachDB, see Third-party Database Tools.