The neo4j.conf file

The neo4j.conf file is the main source of configuration settings in Neo4j and includes the mappings of configuration setting keys to values. The location of the neo4j.conf file in the different configurations of Neo4j is listed in Default file locations.

Most of the configuration settings in the neo4j.conf file apply directly to Neo4j itself, but there are also other settings related to the Java Runtime (the JVM) on which Neo4j runs. For more information, see the JVM specific configuration settings. Many of the configuration settings are also used by neo4j launcher scripts.

neo4j.conf conventions

The syntax in the neo4j.conf file follows the following conventions:

  • The equals sign (=) maps configuration setting keys to configuration values.

  • Lines that start with the number sign (#) are handled as comments.

  • Trailing comments are not supported.

  • Empty lines are ignored.

  • Configuring a setting in neo4j.conf overwrites any default values. If you want to amend the default values with custom ones, you must explicitly list the default values along with the new ones.

  • The configuration settings are not ordered.

  • The configuration settings have strict validation enabled by default. It prevents Neo4j from starting if the neo4j.conf file contains typos, incorrect information, or duplicates (except for server.jvm.additional). If you set more than one value for server.jvm.additional, each setting value adds another custom JVM argument to the java launcher.

    To disable the strict validation, set server.config.strict_validation.enabled=false.

  • By default, the character encoding is assumed to be ISO 8859-1. From Neo4j 4.8 onwards, this can be overridden by setting the environment variable NEO4J_CONFIG_FILE_CHARSET to, for example, utf8.

Configuration settings

General synopsis

Neo4j configuration settings have the following general synopsis:

<prefix>.<scope>.<component>…​.<component>.<name>

Prefix

Prefixes are reserved for denoting two special cases (most settings do not have a prefix):

  • initial — Settings that are only used during the initialization but are ignored thereafter. For example, initial.server.mode_constraint, initial.dbms.default_database, etc.

  • internal — The prefix replaces the terms unsupported and experimental used in previous versions. This namespace is dedicated to features that are used internally and may change without notice.

Scope

All configuration settings fall into one of the following scopes that behave differently:

  • db settings can be varied between each database but must be consistent across all configuration files in a cluster/DBMS.

  • dbms settings must be consistent across all configuration files in a cluster/DBMS.

  • server settings apply only to the specific server and can be varied between configuration files across a cluster/DBMS.

  • browser settings apply only to Neo4j Browser.

  • client settings apply only to the client.

    In Neo4j 5, the fabric scope is no longer available. All configuration settings identified by the fabric namespace in the neo4j.conf file are moved into the system database. The Cypher surface is extended to support the Fabric configuration.

    For more information, see Composite databases.
Component

Component namespaces are used to group settings that affect similar systems.

Name

The name of the setting. It may contain a common verb and unit patterns, such as size, enabled, etc. Words are separated by an underscore.

For a complete reference of Neo4j configuration settings, see Configuration settings.

JVM-specific configuration settings

A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs and programs written in other languages that are also compiled in Java bytecode. The Java heap is where the objects of a Java program live. Depending on the JVM implementation, the JVM heap size often determines how and for how long time the virtual machine performs garbage collection.

Table 1. JVM-specific settings
Setting Description

server.memory.heap.initial_size

Sets the initial heap size for the JVM. By default, the JVM heap size is calculated based on the available system resources.

server.memory.heap.max_size

Sets the maximum size of the heap for the JVM. By default, the maximum JVM heap size is calculated based on the available system resources.

server.jvm.additional

Sets additional options for the JVM. The options are set as a string and can vary depending on JVM implementation.

If you want to have good control of the system behavior, it is recommended to set the heap size parameters to the same value to avoid unwanted full garbage collection pauses.

List currently active settings

You can use SHOW SETTINGS to list the currently active configuration settings and their values.

Example 1. List currently active configuration settings
SHOW SETTINGS
YIELD name, value
WHERE name STARTS WITH 'server.default'
RETURN name, value
ORDER BY name
LIMIT 3;
+---------------------------------------------------+
| name                                | value       |
+---------------------------------------------------+
| "server.default_advertised_address" | "localhost" |
| "server.default_listen_address"     | "localhost" |
+---------------------------------------------------+

For information about dynamic settings, see Update dynamic settings and Configuration settings reference.