25.2. Setup and configuration

Neo4j HA can be set up to accommodate differing requirements for load, fault tolerance and available hardware.

In HA mode, Neo4j instances form a cluster. The instances monitor each others' availability to take account of instances joining and leaving the cluster. They elect one instance to be the master, and designate the other instances to be slaves.

For installation instructions of a High Availability cluster see Section 25.6, “High Availability setup tutorial”.

Specifying cluster members

Specify the instances that should form the cluster by supplying ha.initial_hosts, a comma-separated list of URLs. When each instance starts, if it can contact any of the initial hosts, then it will form a cluster with them, otherwise it will start its own cluster.

Note that the parameter is called ha.initial_hosts because it’s only used when instances initially join the cluster. This means that you can extend the cluster without changing the configuration of existing instances.

Server configuration

If you are running Neo4j server, specify org.neo4j.server.database.mode=HA in conf/neo4j-server.properties.

HA server configuration parameters

Parameter Name Description Example value Required?

org.neo4j.server.database.mode

Whether to run as a single server or in HA mode.

single or HA

yes

Database configuration

HA configuration parameters should be supplied alongside general Neo4j parameters in conf/neo4j.properties. There are many configurable parameters, most in most cases it isn’t necessary to modify the default values. The only parameters that need to be specified are ha.server_id and ha.initial_hosts.

HA database configuration parameters

Parameter Name Description Example value Required?

ha.server_id

Id for a cluster instance. Must be unique within the cluster.

1

yes

ha.initial_hosts

A comma-separated list of other members of the cluster to join.

server1:5001,server2:5001

yes

ha.cluster_server

Host & port to bind the cluster management communication.

server1:5001

no

ha.allow_init_cluster

Whether to allow this instance to create a cluster if unable to join.

true

no

ha.default_timeout

Default timeout used for clustering timeouts. Override specific timeout settings with proper values if necessary. This value is the default value for settings ha.heartbeat_interval, ha.paxos_timeout and ha.learn_timeout.

5s

no

ha.heartbeat_interval

How often heartbeat messages should be sent. Defaults to ha.default_timeout.

5s

no

ha.heartbeat_timeout

Timeout for heartbeats between cluster members. Should be at least twice that of ha.heartbeat_interval.

11s

no

ha.broadcast_timeout

Timeout for broadcasting values in cluster. Must consider end-to-end duration of Paxos algorithm. This value is the default value for settings ha.join_timeout and ha.leave_timeout.

30s

no

ha.join_timeout

Timeout for joining a cluster. Defaults to ha.broadcast_timeout.

30s

no

ha.configuration_timeout

Timeout for waiting for configuration from an existing cluster member during cluster join.

1s

no

ha.leave_timeout

Timeout for waiting for cluster leave to finish. Defaults to ha.broadcast_timeout.

30s

no

ha.paxos_timeout

Default timeout for all Paxos timeouts. Defaults to ha.default_timeout. This value is the default value for settings ha.phase1_timeout, ha.phase2_timeout and ha.election_timeout.

5s

no

ha.phase1_timeout

Timeout for Paxos phase 1. Defaults to ha.paxos_timeout.

5s

no

ha.phase2_timeout

Timeout for Paxos phase 2. Defaults to ha.paxos_timeout.

5s

no

ha.learn_timeout

Timeout for learning values. Defaults to ha.default_timeout.

5s

no

ha.election_timeout

Timeout for waiting for other members to finish a role election. Defaults to ha.paxos_timeout.

5s

no

ha.read_timeout

How long a slave will wait for response from master before giving up.

20s

no

ha.state_switch_timeout

Timeout for waiting for instance to become master or slave.

20s

no

ha.lock_read_timeout

Timeout for taking remote (write) locks on slaves. Defaults to ha.read_timeout.

20s

no

ha.max_concurrent_channels_per_slave

Maximum number of connections a slave can have to the master.

20

no

ha.server

Hostname and port to bind the HA server.

my-domain.com:6001

no

ha.slave_only

Whether this instance should only participate as slave in cluster. If set to true, it will never be elected as master.

false

no

ha.branched_data_policy

Policy for how to handle branched data.

keep_last or keep_all or keep_none

no

ha.com_chunk_size

Max size of the data chunks that flows between master and slaves in HA. Bigger size may increase throughput, but may be more sensitive to variations in bandwidth, whereas lower size increases tolerance for bandwidth variations.

2M

no

ha.pull_interval

Interval of pulling updates from master.

10s

no

ha.tx_push_factor

The amount of slaves the master will ask to replicate a committed transaction.

1

no

ha.tx_push_strategy

Push strategy of a transaction to a slave during commit.

fixed or round_robin

no