# Distributed Configuration

This page is referring to OrientDB v1.7 distributed configuration. Look also at Replication and pages.

The distributed configuration is made of 3 files under the config/ directory:

## orientdb-dserver-config.xml

To enable and configure the clustering between nodes, add and enable the OHazelcastPlugin. This task is configured as a Server handler. The default configuration is reported below.

File orientdb-dserver-config.xml:

<handler class="com.orientechnologies.orient.server.hazelcast.OHazelcastPlugin">
<parameters>
<!-- NODE-NAME. IF NOT SET IS AUTO GENERATED THE FIRST TIME THE SERVER RUN -->
<!-- <parameter name="nodeName" value="europe1" /> -->
<parameter name="enabled" value="true" />
<parameter name="configuration.db.default"
value="${ORIENTDB_HOME}/config/default-distributed-db-config.json" /> <parameter name="configuration.hazelcast" value="${ORIENTDB_HOME}/config/hazelcast.xml" />
</parameters>
</handler>


Where:

Parameter Description
enabled To enable or disable the plugin: true to enable it, false to disable it. By default is true
nodeName An optional alias identifying the current node within the cluster. When omitted, a default value is generated as node, example: "node239233932932". By default is commented, so it's automatic generated
configuration.db.default Path of default distributed database configuration. By default is ${ORIENTDB_HOME}/config/default-distributed-db-config.json configuration.hazelcast Path of Hazelcast configuration file, default is ${ORIENTDB_HOME}/config/hazelcast.xml

## default-distributed-db-config.json

This is the JSON file containing the default configuration for distributed databases. The first time a database run in distributed version this file is copied in the database's folder, then every time the cluster shape changes the database specific file is changed.

Default default-distributed-db-config.json file content:

{
"autoDeploy": true,
"hotAlignment": false,
"writeQuorum": 2,
"failureAvailableNodesLessQuorum": false,
"clusters": {
"internal": {
},
"index": {
},
"*": {
"servers" : [ "<NEW_NODE>" ]
}
}
}


Where:

Parameter Description Default value
autoDeploy Auto deploy the database in case the joining node hasn't it. It can be true or false true
hotAlignment In case a node left the cluster hotAlignment the synchronization queue is left or not for hot alignment when the node will join the cluster again. It can be true or false true
readQuorum On "read" operation (record read, query and traverse) is the number of responses to be coherent before to send the response to the client. Set to 1 if you don't want this check at read time 1
writeQuorum On "write" operation (any write on database) is the number of responses to be coherent before to send the response to the client. Set to 1 if you don't want this check at write time. Suggested value is N/2+1 where N is the number of replicas. In this way the quorum is reached only if the majority of nodes are coherent 2
failureAvailableNodesLessQuorum Decide to return error when the available nodes are less then quorum. Can be true or false false
readYourWrites The write quorum is satisfied only when also the local node responded. This assure current the node can read its writes. Disable it to improve replication performance if such consistency is not important. Can be true or false true
clusters if the object containing the clusters' configuration as map cluster-name : cluster-configuration. * means all the clusters and is the cluster's default configuration -

The cluster configuration inherits database configuration, so if you declare "writeQuorum" at database level, all the clusters will inherit that setting unless they define your own. Settings can be:

Parameter Description Default value
readQuorum On "read" operation (record read, query and traverse) is the number of responses to be coherent before to send the response to the client. Set to 1 if you don't want this check at read time 1
writeQuorum On "write" operation (any write on database) is the number of responses to be coherent before to send the response to the client. Set to 1 if you don't want this check at write time. Suggested value is N/2+1 where N is the number of replicas. In this way the quorum is reached only if the majority of nodes are coherent 2
failureAvailableNodesLessQuorum Decide to return error when the available nodes are less then quorum. Can be true or false false
readYourWrites The write quorum is satisfied only when also the local node responded. This assure current the node can read its writes. Disable it to improve replication performance if such consistency is not important. Can be true or false true
servers Is the array of servers where to store the records of cluster empty for internal and index clusters and [ "<NEW_NODE>" ] for cluster * representing any cluster

"<NEW_NODE>" is a special tag that put any new joining node name in the array.

### Default configuration

In the default configuration all the record clusters are replicated but internal, index, because all the changes remain locally to each node (indexing is per node). Every node that joins the cluster shares all the rest of the clusters ("*" settings). Since "readQuorum" is 1 all the reads are executed on the first available node where the local node is preferred if own the requested record. "writeQuorum" to 2 means that all the changes are in at least 2 nodes. If available nodes are less then 2, no error is given because "failureAvailableNodesLessQuorum" is false.

### 100% asynchronous writes

By default writeQuorum is 2. This means that it waits and checks the answer from at least 2 nodes before to send the ACK to the client. If you've more then 2 nodes configured, then starting from the 3rd node the response will be managed asynchronously. You could also set this to 1 to have all the writes asynchronous.

## hazelcast.xml

A OrientDB cluster is composed by two or more servers that are the nodes of the cluster. All the server nodes that want to be part of the same cluster must to define the same Cluster Group. By default "orientdb" is the group name. Look at the default config/hazelcast.xml configuration file reported below:

<?xml version="1.0" encoding="UTF-8"?>
<hazelcast xsi:schemaLocation="http://www.hazelcast.com/schema/config hazelcast-config-3.0.xsd"
xmlns="http://www.hazelcast.com/schema/config" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<group>
<name>orientdb</name>
</group>
<network>
<port auto-increment="true">2434</port>
<join>
<multicast enabled="true">
<multicast-group>235.1.1.1</multicast-group>
<multicast-port>2434</multicast-port>
</multicast>
</join>
</network>
<executor-service>
<pool-size>16</pool-size>
</executor-service>
</hazelcast>


NOTE: Change the name and password of the group to prevent external nodes from joining it!

### Network configuration

#### Automatic discovery in LAN using Multicast

OrientDB by default uses TCP Multicast to discover nodes. This is contained in config/hazelcast.xml file under the network tag. This is the default configuration:

<hazelcast>
...
<network>
<port auto-increment="true">2434</port>
<join>
<multicast enabled="true">
<multicast-group>235.1.1.1</multicast-group>
<multicast-port>2434</multicast-port>
</multicast>
</join>
</network>
...
</hazelcast>


#### Manual IP

When Multicast is disabled or you prefer to assign Hostnames/IP-addresses manually use the TCP/IP tag in configuration. Pay attention to disable the multicast:

<hazelcast>
...
<network>
<port auto-increment="true">2434</port>
<join>
<multicast enabled="false">
<multicast-group>235.1.1.1</multicast-group>
<multicast-port>2434</multicast-port>
</multicast>
<tcp-ip enabled="true">
<member>europe0:2434</member>
<member>europe1:2434</member>
<member>usa0:2434</member>
<member>asia0:2434</member>
<member>192.168.1.0-7:2434</member>
</tcp-ip>
</join>
</network>
...
</hazelcast>


#### WAN

To setup the Orient server cluster across a WAN look at Hazelcast Config WAN.

#### Cloud support

Since multicast is disabled on most of the Cloud stacks, you have to change the config/hazelcast.xml configuration file based on the Cloud used.

##### Amazon EC2

OrientDB supports natively Amazon EC2 through the Hazelcast's Amazon discovery plugin. In order to use it include also the hazelcast-cloud.jar library under the lib/ directory.

<hazelcast>
...
<join>
<multicast enabled="false">
<multicast-group>235.1.1.1</multicast-group>
<multicast-port>2434</multicast-port>
</multicast>
<aws enabled="true">
<access-key>my-access-key</access-key>
<secret-key>my-secret-key</secret-key>
<region>us-west-1</region>                               <!-- optional, default is us-east-1 -->
shouldn't be set as it will override this property -->
<security-group-name>hazelcast-sg</security-group-name>  <!-- optional -->
<tag-key>type</tag-key>                                  <!-- optional -->
<tag-value>hz-nodes</tag-value>                          <!-- optional -->
</aws>
</join>
...
</hazelcast>


##### Other Cloud providers

Uses manual IP like explained in Manual IP.

## Misc

The simplest and most powerful way to achieve load balancing seems to use some hidden (to some) properties of DNS. The trick is to create a TXT record listing the servers.

The format is:

v=opf<version> (s=<hostname[:<port>]> )*


Example of TXT record for domain dbservers.mydomain.com:

v=opf1 s=192.168.0.101:2424 s=192.168.0.133:2424


In this way if you open a database against the URL remote:dbservers.mydomain.com/demo the OrientDB client library will try to connect to the address 192.168.0.101 port 2424. If the connection fails, then the next address 192.168.0.133: port 3434 is tried.

To enable this feature in Java Client driver set network.binary.loadBalancing.enabled=true:

java ... -Dnetwork.binary.loadBalancing.enabled=true


or via Java code:

OGlobalConfiguration.NETWORK_BINARY_DNS_LOADBALANCING_ENABLED.setValue(true);


## History

### 1.7

Simplified configuration by moving. Removed some flags (replication:boolean, now it’s deducted by the presence of “servers” field) and settings now are global (autoDeploy, hotAlignment, offlineMsgQueueSize, readQuorum, writeQuorum, failureAvailableNodesLessQuorum, readYourWrites), but you can overwrite them per-cluster.