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Apache Solr

Solr is the popular, blazing fast open source enterprise search platform from the Apache Lucene project. Solr is a standalone enterprise search server with a REST-like API. Solr is highly reliable, scalable and fault tolerant, providing distributed indexing, replication and load-balanced querying, automated failover and recovery, centralized configuration and more.

— Apache Solr Homepage

JanusGraph supports Apache Solr as an index backend. Here are some of the Solr features supported by JanusGraph:

  • Full-Text: Supports all Text predicates to search for text properties that matches a given word, prefix or regular expression.
  • Geo: Supports all Geo predicates to search for geo properties that are intersecting, within, disjoint to or contained in a given query geometry. Supports points, lines and polygons for indexing. Supports circles, boxes and polygons for querying point properties and all shapes for querying non-point properties.
  • Numeric Range: Supports all numeric comparisons in Compare.
  • TTL: Supports automatically expiring indexed elements.
  • Temporal: Millisecond granularity temporal indexing.
  • Custom Analyzer: Choose to use a custom analyzer

Please see Version Compatibility for details on what versions of Solr will work with JanusGraph.

Solr Configuration Overview

JanusGraph supports Solr running in either a SolrCloud or Solr Standalone (HTTP) configuration for use with a mixed index (see Mixed Index). The desired connection mode is configured via the parameter mode which must be set to either cloud or http, the former being the default value. For example, to explicitly specify that Solr is running in a SolrCloud configuration the following property is specified as a JanusGraph configuration property:

index.search.solr.mode=cloud

These are some key Solr terms:

  • Core: A single index on a single machine
  • Configuration: solrconfig.xml, schema.xml, and other files required to define a core.
  • Collection: A single logical index that can span multiple cores on different machines.
  • Configset: A shared configuration that can be reused by multiple cores.

Connecting to SolrCloud

When connecting to a SolrCloud cluster by setting the mode equal to cloud, the Zookeeper URL (and optionally port) must be specified so that JanusGraph can discover and interact with the Solr cluster.

index.search.backend=solr
index.search.solr.mode=cloud
index.search.solr.zookeeper-url=localhost:2181

A number of additional configuration options pertaining to the creation of new collections (which is only supported in SolrCloud operation mode) can be configured to control sharding behavior among other things. Refer to the Configuration Reference for a complete listing of those options.

SolrCloud leverages Zookeeper to coordinate collection and configset information between the Solr servers. The use of Zookeeper with SolrCloud provides the opportunity to significantly reduce the amount of manual configuration required to use Solr as a back end index for JanusGraph.

Configset Configuration

A configset is required to create a collection. The configset is stored in Zookeeper to enable access to it across the Solr servers.

  • Each collection can provide its own configset when it is created, so that each collection may have a different configuration. With this approach, each collection must be created manually.

  • A shared configset can be uploaded separately to Zookeeper if it will be reused by multiple collections. With this approach, JanusGraph can create collections automatically by using the shared configset. Another benefit is that reusing a configset significantly reduces the amount of data stored in Zookeeper.

Using an Individual Configset

In this example, a collection named verticesByAge is created manually using the default JanusGraph configuration for Solr that is found in the distribution. When the collection is created, the configuration is uploaded into Zookeeper, using the same collection name verticesByAge for the configset name. Refer to the Solr Reference Guide for available parameters.

# create the collection
$SOLR_HOME/bin/solr create -c verticesByAge -d $JANUSGRAPH_HOME/conf/solr

Define a mixed index using JanusGraphManagement and the same collection name.

mgmt = graph.openManagement()
age = mgmt.makePropertyKey("age").dataType(Integer.class).make()
mgmt.buildIndex("verticesByAge", Vertex.class).addKey(age).buildMixedIndex("search")
mgmt.commit()

Using a Shared Configset

When using a shared configset, it is most convenient to upload the configuration first as a one time operation. In this example, a configset named janusgraph-configset is uploaded in to Zookeeper using the default JanusGraph configuration for Solr that is found in the distribution. Refer to the Solr Reference Guide for available parameters.

# upload the shared configset into Zookeeper
# Solr 5
$SOLR_HOME/server/scripts/cloud-scripts/zkcli.sh -cmd upconfig -z localhost:2181 \
    -d $JANUSGRAPH_HOME/conf/solr -n janusgraph-configset
# Solr 6 and higher
$SOLR_HOME/bin/solr zk upconfig -d $JANUSGRAPH_HOME/conf/solr -n janusgraph-configset \
    -z localhost:2181

When configuring the SolrCloud indexing backend for JanusGraph, make sure to provide the name of the shared configset using the index.search.solr.configset property.

index.search.backend=solr
index.search.solr.mode=cloud
index.search.solr.zookeeper-url=localhost:2181
index.search.solr.configset=janusgraph-configset

Define a mixed index using JanusGraphManagement and the collection name.

mgmt = graph.openManagement()
age = mgmt.makePropertyKey("age").dataType(Integer.class).make()
mgmt.buildIndex("verticesByAge", Vertex.class).addKey(age).buildMixedIndex("search")
mgmt.commit()

Connecting to Solr Standalone (HTTP)

When connecting to Solr Standalone via HTTP by setting the mode equal to http, a single or list of URLs for the Solr instances must be provided.

index.search.backend=solr
index.search.solr.mode=http
index.search.solr.http-urls=http://localhost:8983/solr

Additional configuration options for controlling the maximum number of connections, connection timeout and transmission compression are available for the HTTP mode. Refer to the Configuration Reference for a complete listing of those options.

Core Configuration

Solr Standalone is used for a single instance, and it keeps configuration information on the file system. A core must be created manually for each mixed index.

To create a core, a core_name and a configuration directory is required. Refer to the Solr Reference Guide for available parameters. In this example, a core named verticesByAge is created using the default JanusGraph configuration for Solr that is found in the distribution.

$SOLR_HOME/bin/solr create -c verticesByAge -d $JANUSGRAPH_HOME/conf/solr

Define a mixed index using JanusGraphManagement and the same core name. 

mgmt = graph.openManagement()
age = mgmt.makePropertyKey("age").dataType(Integer.class).make()
mgmt.buildIndex("verticesByAge", Vertex.class).addKey(age).buildMixedIndex("search")
mgmt.commit()

Solr Schema Design

Dynamic Field Definition

By default, JanusGraph uses Solr’s Dynamic Fields feature to define the field types for all indexed keys. This requires no extra configuration when adding property keys to a mixed index backed by Solr and provides better performance than schemaless mode.

JanusGraph assumes the following dynamic field tags are defined in the backing Solr collection’s schema.xml file. Please note that there is additional xml definition of the following fields required in a solr schema.xml file in order to use them. Reference the example schema.xml file provided in the ./conf/solr/schema.xml directory in a JanusGraph installation for more information.

<dynamicField name="*_i"    type="int"          indexed="true"  stored="true"/>
<dynamicField name="*_s"    type="string"       indexed="true"  stored="true" />
<dynamicField name="*_l"    type="long"         indexed="true"  stored="true"/>
<dynamicField name="*_t"    type="text_general" indexed="true"  stored="true"/>
<dynamicField name="*_b"    type="boolean"      indexed="true" stored="true"/>
<dynamicField name="*_f"    type="float"        indexed="true"  stored="true"/>
<dynamicField name="*_d"    type="double"       indexed="true"  stored="true"/>
<dynamicField name="*_g"    type="geo"          indexed="true"  stored="true"/>
<dynamicField name="*_dt"   type="date"         indexed="true"  stored="true"/>
<dynamicField name="*_uuid" type="uuid"         indexed="true"  stored="true"/>

In JanusGraph’s default configuration, property key names do not have to end with the type-appropriate suffix to take advantage of Solr’s dynamic field feature. JanusGraph generates the Solr field name from the property key name by encoding the property key definition’s numeric identifier and the type-appropriate suffix. This means that JanusGraph uses synthetic field names with type-appropriate suffixes behind the scenes, regardless of the property key names defined and used by application code using JanusGraph. This field name mapping can be overridden through non-default configuration. That’s described in the next section.

Manual Field Definition

If the user would rather manually define the field types for each of the indexed fields in a collection, the configuration option dyn-fields needs to be disabled. It is important that the field for each indexed property key is defined in the backing Solr schema before the property key is added to the index.

In this scenario, it is advisable to enable explicit property key name to field mapping in order to fix the field names for their explicit definition. This can be achieved in one of two ways:

  1. Configuring the name of the field by providing a mapped-name parameter when adding the property key to the index. See Individual Field Mapping for more information.
  2. By enabling the map-name configuration option for the Solr index which will use the property key name as the field name in Solr. See Global Field Mapping for more information.

Schemaless Mode

JanusGraph can also interact with a SolrCloud cluster that is configured for schemaless mode. In this scenario, the configuration option dyn-fields should be disabled since Solr will infer the field type from the values and not the field name.

Note, however, that schemaless mode is recommended only for prototyping and initial application development and NOT recommended for production use.

Troubleshooting

Collection Does Not Exist

The collection (and all of the required configuration files) must be initialized before a defined index can use the collection. See Connecting to SolrCloud for more information.

When using SolrCloud, the Zookeeper zkCli.sh command line tool can be used to inspect the configurations loaded into Zookeeper. Also verify that the default JanusGraph configuration files are copied to the correct location under solr and that the directory where the files are copied is correct.

Cannot Find the Specified Configset

When using SolrCloud, a configset is required to create a mixed index for JanusGraph. See Configset Configuration for more information.

  • If using an individual configset, the collection must be created manually first.
  • If using a shared configset, the configset must be uploaded into Zookeeper first.

You can verify that the configset and its configuration files are in Zookeeper under /configs. Refer to the Solr Reference Guide for other Zookeeper operations.

# verify the configset in Zookeeper
# Solr 5
$SOLR_HOME/server/scripts/cloud-scripts/zkcli.sh -cmd list -z localhost:2181
# Solr 6 and higher
$SOLR_HOME/bin/solr zk ls -r /configs/configset-name -z localhost:2181

HTTP Error 404

This error may be encountered when using Solr Standalone (HTTP) mode. An example of the error:

20:01:22 ERROR org.janusgraph.diskstorage.solr.SolrIndex  - Unable to save documents
to Solr as one of the shape objects stored were not compatible with Solr.
org.apache.solr.client.solrj.impl.HttpSolrClient$RemoteSolrException: Error from server
at http://localhost:8983/solr: Expected mime type application/octet-stream but got text/html.
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 404 Not Found</title>
</head>
<body><h2>HTTP ERROR 404</h2>
<p>Problem accessing /solr/verticesByAge/update. Reason:
<pre>    Not Found</pre></p>
</body>
</html>

Make sure to create the core manually before attempting to store data into the index. See Core Configuration for more information.

Invalid core or collection name

The core or collection name is an identifier. It must consist entirely of periods, underscores, hyphens, and/or alphanumerics, and also it may not start with a hyphen.

Connection Problems

Irrespective of the operation mode, a Solr instance or a cluster of Solr instances must be running and accessible from the JanusGraph instance(s) in order for JanusGraph to use Solr as an indexing backend. Check that the Solr cluster is running correctly and that it is visible and accessible over the network (or locally) from the JanusGraph instances.

JTS ClassNotFoundException with Geo Data

Solr relies on Spatial4j for geo processing. Spatial4j declares an optional dependency on JTS ("JTS Topology Suite"). JTS is required for some geo field definition and query functionality. If the JTS jar is not on the Solr daemon’s classpath and a field in schema.xml uses a geo type, then Solr may throw a ClassNotFoundException on one of the missing JTS classes. The exception can appear when starting Solr using a schema.xml file designed to work with JanusGraph, but can also appear when invoking CREATE in the Solr CoreAdmin API. The exception appears in slightly different formats on the client and server sides, although the root cause is identical.

Here’s a representative example from a Solr server log:

ERROR [http-8983-exec-5] 2014-10-07 02:54:06, 665 SolrCoreResourceManager.java (line 344) com/vividsolutions/jts/geom/Geometry
java.lang.NoClassDefFoundError: com/vividsolutions/jts/geom/Geometry
    at com.spatial4j.core.context.jts.JtsSpatialContextFactory.newSpatialContext(JtsSpatialContextFactory.java:30)
    at com.spatial4j.core.context.SpatialContextFactory.makeSpatialContext(SpatialContextFactory.java:83)
    at org.apache.solr.schema.AbstractSpatialFieldType.init(AbstractSpatialFieldType.java:95)
    at org.apache.solr.schema.AbstractSpatialPrefixTreeFieldType.init(AbstractSpatialPrefixTreeFieldType.java:43)
    at org.apache.solr.schema.SpatialRecursivePrefixTreeFieldType.init(SpatialRecursivePrefixTreeFieldType.java:37)
    at org.apache.solr.schema.FieldType.setArgs(FieldType.java:164)
    at org.apache.solr.schema.FieldTypePluginLoader.init(FieldTypePluginLoader.java:141)
    at org.apache.solr.schema.FieldTypePluginLoader.init(FieldTypePluginLoader.java:43)
    at org.apache.solr.util.plugin.AbstractPluginLoader.load(AbstractPluginLoader.java:190)
    at org.apache.solr.schema.IndexSchema.readSchema(IndexSchema.java:470)
    at com.datastax.bdp.search.solr.CassandraIndexSchema.readSchema(CassandraIndexSchema.java:72)
    at org.apache.solr.schema.IndexSchema.<init>(IndexSchema.java:168)
    at com.datastax.bdp.search.solr.CassandraIndexSchema.<init>(CassandraIndexSchema.java:54)
    at com.datastax.bdp.search.solr.core.CassandraCoreContainer.create(CassandraCoreContainer.java:210)
    at com.datastax.bdp.search.solr.core.SolrCoreResourceManager.createCore(SolrCoreResourceManager.java:256)
    at com.datastax.bdp.search.solr.handler.admin.CassandraCoreAdminHandler.handleCreateAction(CassandraCoreAdminHandler.java:117)
    ...

Here’s what normally appears in the output of the client that issued the associated CREATE command to the CoreAdmin API:

org.apache.solr.common.SolrException: com/vividsolutions/jts/geom/Geometry
    at com.datastax.bdp.search.solr.core.SolrCoreResourceManager.createCore(SolrCoreResourceManager.java:345)
    at com.datastax.bdp.search.solr.handler.admin.CassandraCoreAdminHandler.handleCreateAction(CassandraCoreAdminHandler.java:117)
    at org.apache.solr.handler.admin.CoreAdminHandler.handleRequestBody(CoreAdminHandler.java:152)
    ...

This is resolved by adding the JTS jar to the classpath of JanusGraph and/or the Solr server. JTS is not included in JanusGraph distributions by default due to its LGPL license. Users must download the JTS jar file separately and copy it into the JanusGraph and/or Solr server lib directory. If using Solr’s built in web server, the JTS jar may be copied to the example/solr-webapp/webapp/WEB-INF/lib directory to include it in the classpath. Solr can be restarted, and the exception should be gone. Solr must be started once with the correct schema.xml file in place first, for the example/solr-webapp/webapp/WEB-INF/lib directory to exist.

To determine the ideal JTS version for Solr server, first check the version of Spatial4j in use by the Solr cluster, then determine the version of JTS against which that Spatial4j version was compiled. Spatial4j declares its target JTS version in the pom for the com.spatial4j:spatial4j artifact. Copy the JTS jar to the server/solr-webapp/webapp/WEB-INF/lib directory in your solr installation.

Advanced Solr Configuration

This section covers installation and configuration of JanusGraph with DataStax Enterprise (DSE) Search. There are multiple ways to install DSE, but this section focuses on DSE’s binary tarball install option on Linux. Most of the steps in this section can be generalized to the other install options for DSE.

Install DataStax Enterprise as directed by the page Installing DataStax Enterprise using the binary tarball.

Export DSE_HOME and append to PATH in your shell environment. Here’s an example using Bash syntax: 

export DSE_HOME=/path/to/dse-version.number
export PATH="$DSE_HOME"/bin:"$PATH"

Install JTS for Solr. The appropriate version varies with the Spatial4j version. As of DSE 4.5.2, the appropriate version is 1.13. 

cd $DSE_HOME/resources/solr/lib
curl -O 'http://central.maven.org/maven2/com/vividsolutions/jts/1.13/jts-1.13.jar'

Start DSE Cassandra and Solr in a single background daemon:

# The "dse-data" path below was chosen to match the
# "Installing DataStax Enterprise using the binary tarball"
# documentation page from DataStax.  The exact path is not
# significant.
dse cassandra -s -Ddse.solr.data.dir="$DSE_HOME"/dse-data/solr

The previous command will write some startup information to the console and to the logfile path log4j.appender.R.File configured in $DSE_HOME/resources/cassandra/conf/log4j-server.properties.

Once DSE with Cassandra and Solr has started normally, check the cluster health with nodetool status. A single-instance ring should show one node with flags *U*p and *N*ormal:

nodetool status
Note: Ownership information does not include topology; for complete information, specify a keyspace
= Datacenter: Solr
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address    Load       Owns   Host ID                               Token                                    Rack
UN  127.0.0.1  99.89 KB   100.0%  5484ef7b-ebce-4560-80f0-cbdcd9e9f496  -7317038863489909889                     rack1

Next, switch to Gremlin Console and open a JanusGraph database against the DSE instance. This will create JanusGraph’s keyspace and column families.

cd $JANUSGRAPH_HOME
bin/gremlin.sh

         \,,,/
         (o o)
-----oOOo-(3)-oOOo-----
gremlin> graph = JanusGraphFactory.open('conf/janusgraph-cql-solr.properties')
==>janusgraph[cql:[127.0.0.1]]
gremlin> g = graph.traversal()
==>graphtraversalsource[janusgraph[cql:[127.0.0.1]], standard]
gremlin>

Keep this Gremlin Console open. We’ll take a break now to install a Solr core. Then we’ll come back to this console to load some sample data.

Next, upload configuration files for JanusGraph’s Solr collection, then create the core in DSE:

# Change to the directory where JanusGraph was extracted.  Later commands
# use relative paths to the Solr config files shipped with the JanusGraph
# distribution.
cd $JANUSGRAPH_HOME

# The name must be URL safe and should contain one dot/full-stop
# character. The part of the name after the dot must not conflict with
# any of JanusGraph's internal CF names.  Starting the part after the dot
# "solr" will avoid a conflict with JanusGraph's internal CF names.
CORE_NAME=janusgraph.solr1
# Where to upload collection configuration and send CoreAdmin requests.
SOLR_HOST=localhost:8983

# The value of index.[X].solr.http-urls in JanusGraph's config file
# should match $SOLR_HOST and $CORE_NAME.  For example, given the
# $CORE_NAME and $SOLR_HOST values above, JanusGraph's config file would
# contain (assuming "search" is the desired index alias):
#
# index.search.solr.http-urls=http://localhost:8983/solr/janusgraph.solr1
#
# The stock JanusGraph config file conf/janusgraph-cql-solr.properties
# ships with this http-urls value.

# Upload Solr config files to DSE Search daemon
for xml in conf/solr/{solrconfig, schema, elevate}.xml ; do
    curl -v http://"$SOLR_HOST"/solr/resource/"$CORE_NAME/$xml" \
      --data-binary @"$xml" -H 'Content-type:text/xml; charset=utf-8'
done
for txt in conf/solr/{protwords, stopwords, synonyms}.txt ; do
    curl -v http://"$SOLR_HOST"/solr/resource/"$CORE_NAME/$txt" \
      --data-binary @"$txt" -H 'Content-type:text/plain; charset=utf-8'
done
sleep 5

# Create core using the Solr config files just uploaded above
curl "http://"$SOLR_HOST"/solr/admin/cores?action=CREATE&name=$CORE_NAME"
sleep 5

# Retrieve and print the status of the core we just created
curl "http://localhost:8983/solr/admin/cores?action=STATUS&core=$CORE_NAME"

Now the JanusGraph database and backing Solr core are ready for use. We can test it out with the Graph of the Gods dataset. Picking up the Gremlin Console session started above: 

// Assuming graph = JanusGraphFactory.open('conf/janusgraph-cql-solr.properties')...
gremlin> GraphOfTheGodsFactory.load(graph)
==>null

Now we can run any of the queries described in Getting started. Queries involving text and geo predicates will be served by Solr. For more verbose reporting from JanusGraph and the Solr client, run gremlin.sh -l DEBUG and issue some index-backed queries.