Introduction
Concepts
With Neo4j 4.1 you can create and use more than one active database at the same time.
- DBMS
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Neo4j is a Database Management System, or DBMS, capable of managing multiple databases. The DBMS can manage a standalone server, or a group of servers in a Causal Cluster.
- Instance
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A Neo4j instance is a Java process that is running the Neo4j server code.
- Transaction domain
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A transaction domain is a collection of graphs that can be updated within the context of a single transaction.
- Execution context
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An execution context is a runtime environment for the execution of a request. In practical terms, a request may be a query, a transaction, or an internal function or procedure.
- Database
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A database is an administrative partition of a DBMS. In practical terms, it is a physical structure of files organized within a directory or folder, that has the same name of the database. In logical terms, a database is a container for one or more graphs.
A database defines a transaction domain and an execution context. This means that a transaction cannot span across multiple databases. Similarly, a procedure is called within a database, although its logic may access data that is stored in other databases.
A default installation of Neo4j 4.1 contains two databases:
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system- the system database, containing metadata on the DBMS and security configuration. -
neo4j- the default database, a single database for user data. This has a default name ofneo4j. A different name can be configured before starting Neo4j for the first time.
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- Graph
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This is a data model within a database. In Neo4j 4.0 there is only one graph within each database, and many administrative commands that refer to a specific graph do so using the database name.
In Neo4j Fabric, it is possible to refer to multiple graphs within the same transaction and Cypher query.
The following image illustrates a default installation, including the system database and a single database named neo4j for user data:
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Editions
The edition of Neo4j determines the number of possible databases:
All installations include the |
The system database
All installations include a built-in database named system, which contains meta-data and security configuration.
The system database behaves differently than all other databases.
In particular, when connected to this database you can only perform a specific set of administrative functions, as described in detail in Cypher Manual → Administration.
Most of the available administrative commands are restricted to users with specific administrative privileges. An example of configuring security privileges is described in Fine-grained access control. Security administration is described in detail in Cypher Manual → Security of administration .
The following image illustrates an installation of Neo4j with multiple active databases, named marketing, sales, and hr:
The default database
Each Neo4j instance has a default database. If a user connects to Neo4j without specifying a database, it will connect to the default database.
The default database is configurable. See configuration parameters for details.
The following image illustrates an installation of Neo4j containing the three databases for user data, named marketing, sales and hr, and the system database.
The default database is sales:
