This section applies to Virtuoso as of version 6.x and higher.

This documentation details how to configure the Subordinate (also called Slave) Nodes of a Virtuoso Elastic Cluster to service HTTP clients.

By default, only the Primary (also called Master) instance of a Virtuoso Elastic Cluster is configured to provide HTTP services.

The Subordinate (also called Slave) nodes of the cluster may also be configured to provide HTTP services, enabling load balancing by spreading HTTP requests across the cluster's nodes.

This documentation details the steps for the installation and configuration of a Virtuoso Elastic Cluster on Unix:

  1. Step 1

    : Set up each instance as a HTTP Server;

  2. Step 2

    : Install and configure HTTP services on each instance;

  3. Step 3

    : Configure load balancing.

Step 1 : Set up each instance as a HTTP Server

Each node can be configured to provide HTTP services as follows:

  1. Copy the [HTTP Server] section from the Primary instance's configuration file (by default, virtuoso.ini ) to the configuration file of each Subordinate instance:

    ServerPort                  = 8890
    ServerRoot                  = ../vsp
    DavRoot                     = DAV
    EnabledDavVSP               = 0
    HTTPProxyEnabled            = 0
    TempASPXDir                 = 0
    DefaultMailServer           = localhost:25
    MaxClientConnections        = 5
    MaxKeepAlives               = 10
    KeepAliveTimeout            = 10
    MaxCachedProxyConnections   = 10
    ProxyConnectionCacheTimeout = 15
    HTTPThreadSize              = 280000
    HttpPrintWarningsInOutput   = 0
    Charset                     = UTF-8
    ;HTTPLogFile                 = logs/http.log
    MaintenancePage             = atomic.html
    EnabledGzipContent          = 1
  2. Edit the ServerPort parameter to make it unique on the machine hosting this instance; i.e., if a subordinate instance is running on same physical node as the primary instance, then the subordinate's HTTP port must to be changed (from 8890, for instance) to a unique port (e.g., 8891).

  3. Install the Virtuoso Conductor to enable HTTP Administration of the instance being configured. Note: if the subordinate instance is not on the same machine as the primary instance, then the vad directory may also need to be copied from the primary instance to the subordinate instance.:

    SQL> vad_install ('../vad/conductor_dav.vad', 0);
    00000    No errors detected
    00000    Installation of "Virtuoso Conductor" is complete.
    00000    Now making a final checkpoint.
    00000    Final checkpoint is made.
    00000    SUCCESS
    6 Rows. -- 10263 msec.

Step 2 : Install and configure HTTP services on each instance

Any HTTP services required on the subordinate instance will need to specifically installed or configured on that physical node. For example, the Virtuoso default SPARQL endpoint (/sparql ) may be configured by:

  1. Log in into the Virtuoso Conductor http://hostname:port/conductor :

    Figure 2.185. Configure SPARQL Endpoint: log in

    Configure SPARQL Endpoint: log in

  2. Go the the Web Application Server -> Virtual Domains & Directories tab:

    Figure 2.186. Configure SPARQL Endpoint: Virtual Domains and Directories

    Configure SPARQL Endpoint: Virtual Domains and Directories

  3. Select the New Directory Action for the Default Web Site HTTP host:

    Figure 2.187. Configure SPARQL Endpoint: new directory

    Configure SPARQL Endpoint: new directory

  4. Select the Type radio button and SPARQL access point item from the drop down list box:

    Figure 2.188. Configure SPARQL Endpoint: set type SPARQL

    Configure SPARQL Endpoint: set type SPARQL

  5. Click "Next".

  6. Enter /sparql as the Path param in the Virtual Directory Information section and click Save Changes:

    Figure 2.189. Configure SPARQL Endpoint: set /sparql virtual directory

    Configure SPARQL Endpoint: set /sparql virtual directory

  7. The SPARQL endpoint will not be accessible on http://hostname:port/sparql the the newly configured slave nodes:

    Figure 2.190. Configure SPARQL Endpoint: SPARQL Endpoint

    Configure SPARQL Endpoint: SPARQL Endpoint

  8. Further details on SPARQL endpoint configuration can be found in Service Endpoint documentation section.

  9. Typical Virtuoso server log output from a slave node when started, showing the HTTP server running on port 8890, being:

    20:12:49 OpenLink Virtuoso Universal Server
    20:12:49 Version 07.10.3209-pthreads for Linux as of Apr 26 2014
    20:12:49 uses parts of OpenSSL, PCRE, Html Tidy
    20:12:49 Registered to OpenLink Virtuoso (Internal Use)
    20:12:49 Personal Edition license for 500 connections
    20:12:49 Issued by OpenLink Software
    20:12:49 This license will expire on Sun May 17 06:18:35 2015 GMT
    20:12:49 Enabled Cluster Extension
    20:12:49 Enabled Column Store Extension
    20:12:57 Database version 3126
    20:12:57 SQL Optimizer enabled (max 1000 layouts)
    20:12:58 Compiler unit is timed at 0.000208 msec
    20:12:58 Roll forward started
    20:12:58 Roll forward complete
    20:12:59 Checkpoint started
    20:12:59 Checkpoint finished, log reused
    20:12:59 HTTP/WebDAV server online at 8890
    20:12:59 Server online at 12202 (pid 15969)

Step 3 : Configure load balancing

A reverse-proxy service (like Nginx or Apache) can then be configured such that requests are proxied across as any or all nodes of the cluster, to provide the desired load balancing.

  • Only the Primary Node of an Elastic Cluster may be configured as a Publisher for Virtuoso Replication Cluster purposes.

  • The Virtuoso 500 billion triple Berlin SPARQL Benchmark (BSBM) dataset runs were performed on a 24-node Elastic Cluster. Each node was configured to provide HTTP services and a SPARQL endpoint, and the query load was spread over the entire cluster.