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 but 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.

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.

Neo4j comes with several pre-defined values of the server.jvm.additional setting. You can find them in the neo4j.conf file. The table below lists them and explains their roles.

Table 2. Pre-defined values of server.jvm.additional
Default value Note

server.jvm.additional=-XX:+UseG1GC

G1GC (Garbage-First Garbage Collector) provides a good balance between throughput and tail latency with minimal tuning requirements.

server.jvm.additional=-XX:-OmitStackTraceInFastThrow

Ensures that common exceptions always have stack traces, allowing effective debugging regardless of logs rotation frequency.

server.jvm.additional=-XX:+AlwaysPreTouch

Ensures that initmemory is not only allocated but also committed to the process before the database starts. It is recommended to reduce the heap memory if this flag degrades performance.

server.jvm.additional=-XX:+UnlockExperimentalVMOptions

Trusts that non-static final fields are really final. This allows more optimizations and improves overall performance. Disable this flag if you use embedded mode or have extensions or dependencies that may use reflection or serialization to change the value of final fields.

server.jvm.additional=-XX:+TrustFinalNonStaticFields

server.jvm.additional=-XX:+DisableExplicitGC

Disables explicit garbage collection, which is occasionally invoked by the JDK itself.

server.jvm.additional=-XX:-RestrictContended [1]

Allows Neo4j to use @Contended annotation.

server.jvm.additional=-Djdk.nio.maxCachedBufferSize=1024

Restricts size of cached JDK buffers to 1 KB.

server.jvm.additional=-Dio.netty.tryReflectionSetAccessible=true

Enables Netty to allocate direct buffers more efficiently by allowing reflection-based access to internal JVM APIs. This bypasses the standard JVM cleanup mechanism.

Introduced in 2025.04 server.jvm.additional=-Dio.netty.leakDetection.level=DISABLED

Netty resources leak detection. Possible values are DISABLED, SIMPLE, ADVANCED, and PARANOID. Ignores case. For more details refer to the Netty documentation.

server.jvm.additional=-Djdk.tls.ephemeralDHKeySize=2048

Expands Diffie Hellman (DH) key size from default 1024 to 2048 for DH-RSA cipher suites used in server TLS handshakes. This is to protect the server from any potential passive eavesdropping.

server.jvm.additional=-Djdk.tls.rejectClientInitiatedRenegotiation=true

Mitigates a DDoS vector.

server.jvm.additional=-XX:FlightRecorderOptions=stackdepth=256

Increases the default flight recorder stack sampling depth from 64 to 256, to avoid truncating frames when profiling.

server.jvm.additional=-XX:+UnlockDiagnosticVMOptions

Allows profilers to sample between safepoints. Without this, sampling profilers may produce less accurate results.

server.jvm.additional=-XX:+DebugNonSafepoints

server.jvm.additional=--add-opens=java.base/java.nio=ALL-UNNAMED

Opens modules for Neo4j to allow internal access.

server.jvm.additional=--add-opens=java.base/java.io=ALL-UNNAMED

server.jvm.additional=--add-opens=java.base/sun.nio.ch=ALL-UNNAMED

Introduced in 2025.04 server.jvm.additional=--add-opens=java.base/java.util.concurrent=ALL-UNNAMED

server.jvm.additional=--enable-native-access=ALL-UNNAMED

Enables native memory access.

Introduced in 2026.08 server.jvm.additional=--add-modules=jdk.incubator.vector

Enables access to JDK vector API.

server.jvm.additional=-Dlog4j2.disable.jmx=true

Disables logging JMX endpoint.

server.jvm.additional=-Dlog4j.layout.jsonTemplate.maxStringLength=32768

Increases the JSON log string maximum length.

Introduced in 2026.02 server.jvm.additional=-Dorg.neo4j.shaded.lucene9.vectorization.upperJavaFeatureVersion=25

Allows legacy Lucene indexes to use vector provider in recent JDK.
1. This option is currently listed in the Enterprise Edition, but it also could be added to the Community Edition.

Show 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.

Glossary

allocator

A component in the cluster that allocates databases to servers according to the topology constraints specified and an allocation strategy.

asynchronous replication

Asynchronous replication is used by secondary copies to poll for new transactions, which means they cannot be guaranteed to have received the most recent transactions. This enables efficient scale-out of read-performance.

Aura instance

A fully-managed DBMS represented by a single instance ID, that is running in the Neo4j Aura cloud.

auto-commit transaction

An automatically committed transaction that contains a single query.

Bolt protocol

Bolt is a protocol used for interaction between Neo4j instances and drivers.

bookmark

A marker the client can request from the cluster to ensure that it is able to read its own writes so that the application’s state is consistent and only databases that have a copy of the bookmark are permitted to respond.

category (Bloom)

A category is based on a node label and is defined in a Perspective as a way of visually distinguishing nodes with the same label(s).

causal consistency

All servers in a cluster agree on the order in which transactions take place. The position of a server on the causal chain can be guaranteed using a bookmark.

cluster

A Neo4j DBMS that spans multiple servers working together to increase fault tolerance and/or read scalability. Databases on a cluster may be configured to replicate across servers in the cluster thus achieving read scalability or high availability.

client application

Software that interacts with a Neo4j server.

commit

A commit is the successful completion of a transaction, which ensures durability of any changes made. For more details, visit Operations Manual → Transaction management.

composite database

Composite databases are the means to access partitioned graph data with a single Cypher query.

constraint

Constraints are sets of data modeling rules that ensure the data is consistent and reliable.

Cypher®

Neo4j’s graph query language.

data model

A data model defines how information is organized in a database. A good data model will make querying and understanding your data easier. In Neo4j, the data models have a graph structure.

database

A database is a container used by the DBMS to manage and store graph data. The physical structure of data is controlled by the database.

database vs graph

Databases are the physical containers of graph data. Graphs are the logical structure of data in Neo4j.

Database Management System

Database Management System, or DBMS, capable of managing multiple databases. A DBMS may run on a single server, or span several servers configured as a cluster.

database schema

The prescribed property existence and datatypes for nodes and relationships.

deallocate

An act of removing a database from a server or a server from a cluster without loss of data or reduced fault tolerance.

degree (of a node)

The number of relationships of a specific node; loops are counted twice.

disaster recovery

A manual intervention to restore availability of a cluster, or databases within a cluster.

driver

A software library that provides access to Neo4j from a particular programming language.

election

In the event that the Raft leader becomes unresponsive, followers automatically trigger an election and vote for a new leader.

entity

A node or a relationship.

expression (Cypher)

A component of a Cypher query which produces values. It may be used in projections, as a predicate, or when setting properties on graph elements.

fabric

Fabric is the architectural design of a unified system that provides a single access point to local or distributed graph data.

fault tolerance

A guarantee that a cluster can maintain a database’s persistence and availability in the event of one or more servers failing.

follower

A primary copy of a database acting as a follower, receives and acknowledges synchronous writes from the leader.

Generative AI (GenAI)

A type of artificial intelligence (AI) system that generates text, images, or other media in response to prompts.

graph

A logical representation of a set of nodes where some pairs are connected by relationships.

index

Data structure that improves read performance of a database.

knowledge graph

A specific type of graph that has an organizing principle so that a user (or a computer system) can reason about the underlying data. The organizing principle provides an additional layer of structure that adds context to support knowledge discovery.

label

Marks a node as a member of a named and indexed subset. A node may be assigned zero or more labels.

leader

A single primary copy of a database is designated as the leader. It receives all write transactions from clients and replicates writes synchronously to followers and asynchronously to secondary copies of the database.

main database

In terms of Neo4j Enterprise Studio, the database(s) containing the user’s data. Can exist in the same Neo4j deployment as the tool asset database.

motif

A description of a specific pattern within a graph.

node

A node represents an entity or discrete object in your graph data model. Nodes can be connected by relationships, hold data in properties, and are classified by labels.

operator

A symbol representing a mathematical or logical operation.

parameter

Named value provided when running a Cypher statement.

path

A sequence of nodes and the relationships connecting them, that does not contain duplicate relationships. Several paths can match a pattern.

pattern

A specific arrangement of nodes and relationships that can be matched in a graph. A pattern follows a motif.

perspective (Bloom)

A Perspective defines a certain business view or domain that can be found in the target Neo4j graph. A single Neo4j graph can be viewed through different Perspectives, each tailored for a different business purpose.

primary

A copy of the database that is able to process write transactions and is eligible to be elected as a leader. It participates in fault tolerant writes as it is part of the majority required to acknowledge and commit write transactions.

primary vs secondary

In a cluster, databases can operate in either primary or secondary mode. Primary databases are able to process write and read transactions, ensuring fault tolerance. Secondary databases are replicated asynchronously from primaries, and their main purpose is to provide read scaling within the cluster.

project (Aura)

An isolated environment in the unified Aura console that contains its own database instances, configurations, and resources. Preceded by tenant in the classic Aura console.

property

Properties are key-value pairs that are used for storing data on nodes and relationships.

query (Cypher)

A statement that retrieves or writes information to a database.

Raft group

A group of servers that are participating in hosting a particular database in primary mode.

Raft group member

A server that is participating in a Raft group. A server can be a member of one or more groups.

Raft log

A shared log between all Raft group members that is guaranteed to be consistently updated and viewed by those members. The log contains both database data and operational state of the Raft group.

Raft protocol

The networking mechanism that enables a database to replicate its data across multiple servers to give high availability for accessing the data and high durability to the data stored.

read scaling

Distributing query load by creating additional database copies hosted in secondary mode (read-only).

relationship

A relationship represents a connection between nodes in your graph data model. Relationships connect a source node to a target node, hold data in properties, and are classified by type.

secondary

An asynchronously replicated copy of the database that provides read scaling within the cluster.

seed

A seed is a database dump or a full backup used to create a database on a cluster. This is sometimes called seeding.

server

A physical machine, a virtual machine, or a container running an instance of Neo4j. Servers can be standalone or part of a cluster.

session

A causally linked sequence of transactions.

session consistency

An alternative name for Neo4j’s causal consistency.

standalone

A single server running Neo4j and not part of a cluster.

synchronous replication

Synchronous replication requires the leader primary to replicate a transaction and block the commit until a quorum of the follower primaries acknowledges that the transaction is successfully replicated. Once the transaction is replicated, the commit is allowed to proceed. This ensures data durability and consistency within the cluster.

system database

A database used by Neo4j to store system information.

tenant (Aura)

An isolated environment in the classic Aura console that contains its own database instances, configurations, and resources. Replaced by project in the unified Aura console.

tool asset database

In terms of Neo4j Enterprise Studio, the database where tools' assets are stored. This can be in the same Neo4j deployment as the main database(s) or in a separate deployment.

topology

A configuration that describes how the copies of a database should be spread across the servers in a cluster, see primary mode and secondary mode.

transaction

A transaction comprises a unit of work performed against a database. It is treated in a coherent and reliable way, independent of other transactions. Transactions comply with the ACID consistency model (atomic, consistent, isolated, and durable).