Configuring solr.xml

The solr.xml file defines some global configuration options that apply to all or many cores.

This section will describe the default solr.xml file included with Solr and how to modify it for your needs. For details on how to configure core.properties, see the section Core Discovery.

Defining solr.xml

You can find solr.xml in your $SOLR_HOME directory (usually server/solr or /var/solr/data) or optionally in ZooKeeper when using SolrCloud. If $SOLR_HOME/solr.xml is not found, Solr will use the default solr.xml file.

The default solr.xml file is found in $SOLR_TIP/server/solr/solr.xml and looks like this:

<solr>

  <int name="maxBooleanClauses">${solr.max.booleanClauses:1024}</int>
  <str name="sharedLib">${solr.sharedLib:}</str>
  <str name="modules">${solr.modules:}</str>
  <str name="allowPaths">${solr.allowPaths:}</str>
  <str name="allowUrls">${solr.allowUrls:}</str>

  <solrcloud>

    <str name="host">${host:}</str>
    <int name="hostPort">${solr.port.advertise:0}</int>
    <str name="hostContext">${hostContext:solr}</str>

    <bool name="genericCoreNodeNames">${genericCoreNodeNames:true}</bool>

    <int name="zkClientTimeout">${zkClientTimeout:30000}</int>
    <int name="distribUpdateSoTimeout">${distribUpdateSoTimeout:600000}</int>
    <int name="distribUpdateConnTimeout">${distribUpdateConnTimeout:60000}</int>
    <str name="zkCredentialsProvider">${zkCredentialsProvider:org.apache.solr.common.cloud.DefaultZkCredentialsProvider}</str>
    <str name="zkACLProvider">${zkACLProvider:org.apache.solr.common.cloud.DefaultZkACLProvider}</str>
    <bool name="distributedClusterStateUpdates">${distributedClusterStateUpdates:false}</bool>
    <bool name="distributedCollectionConfigSetExecution">${distributedCollectionConfigSetExecution:false}</bool>

  </solrcloud>

  <shardHandlerFactory name="shardHandlerFactory"
    class="HttpShardHandlerFactory">
    <int name="socketTimeout">${socketTimeout:600000}</int>
    <int name="connTimeout">${connTimeout:60000}</int>
  </shardHandlerFactory>

  <metrics enabled="${metricsEnabled:true}">
    <!--reporter name="jmx_metrics" group="core" class="org.apache.solr.metrics.reporters.SolrJmxReporter"/-->
  </metrics>

</solr>

As you can see, the discovery Solr configuration is "SolrCloud friendly". However, the presence of the <solrcloud> element does not mean that the Solr instance is running in SolrCloud mode. Unless the -DzkHost or -DzkRun are specified at startup time, this section is ignored.

Solr.xml Parameters

The <solr> Element

There are no attributes that you can specify in the <solr> tag, which is the root element of solr.xml. The tables below list the child nodes of each XML element in solr.xml.

configSetService

Optional

Default: configSetService

This attribute does not need to be set.

If used, this attribute should be set to the FQN (Fully qualified name) of a class that inherits from ConfigSetService, and you must provide a constructor with one parameter which the type is org.apache.solr.core.CoreContainer. For example, <str name="configSetService">com.myorg.CustomConfigSetService</str>.

If this attribute isn’t set, Solr uses the default configSetService, with zookeeper aware of org.apache.solr.cloud.ZkConfigSetService, without zookeeper aware of org.apache.solr.core.FileSystemConfigSetService.

adminHandler

Optional

Default: org.apache.solr.handler.admin.CoreAdminHandler

This attribute does not need to be set.

If used, this attribute should be set to the FQN (Fully qualified name) of a class that inherits from CoreAdminHandler. For example, <str name="adminHandler">com.myorg.MyAdminHandler</str> would configure the custom admin handler (MyAdminHandler) to handle admin requests.

If this attribute isn’t set, Solr uses the default admin handler, org.apache.solr.handler.admin.CoreAdminHandler.

collectionsHandler

Optional

Default: none

As above, for custom CollectionsHandler implementations.

infoHandler

Optional

Default: none

As above, for custom InfoHandler implementations.

coreLoadThreads

Optional

Default: none

Specifies the number of threads that will be assigned to load cores in parallel.

replayUpdatesThreads

Optional

Default: see description

Specifies the number of threads that will be assigned to replay updates in parallel. This pool is shared for all cores of the node. The default value is equal to the number of processors.

coreRootDirectory

Optional

Default: server/solr

The root of the core discovery tree, defaults to $SOLR_HOME.

managementPath

Optional

Default: none

Currently non-operational.

sharedLib

Optional

Default: none

Specifies the path to a common library directory that will be shared across all cores. Any JAR files in this directory will be added to the search path for Solr plugins. If the specified path is not absolute, it will be relative to $SOLR_HOME. Custom handlers may be placed in this directory. Note that specifying sharedLib will not remove $SOLR_HOME/lib from Solr’s class path.

modules

Optional

Default: none

Takes a list of bundled solr modules to add to Solr’s class path on startup. This way of adding modules will add them to the shared class loader, making them available for every collection in Solr, unlike <lib> tag in solrconfig.xml which is only for that one collection. Example value: extracting,ltr. See the Solr Modules chapter for more details.

allowPaths

Optional

Default: none

Solr will normally only access folders relative to $SOLR_HOME, $SOLR_DATA_HOME or coreRootDir. If you need to e.g., create a core outside of these paths, you can explicitly allow the path with allowPaths. It is a comma separated string of file system paths to allow. The special value of * will allow any path on the system.

allowUrls

Optional

Default: see description

Comma-separated list of Solr hosts to allow.

The HTTP/HTTPS protocol may be omitted, and only the host and port are checked, i.e., 10.0.0.1:8983/solr,10.0.0.1:8984/solr.

When running Solr as a user-managed cluster and using the shards parameter, a list of hosts needs to be specifically configured as allowed or Solr will forbid the request.

In SolrCloud mode, the allow-list is automatically configured to include all live nodes in the cluster.

The allow-list can also be configured with the solr.allowUrls system property in solr.in.sh / solr.in.cmd. If you need to disable this feature for backwards compatibility, you can set the system property solr.disable.allowUrls=true.

shareSchema

Optional

Default: none

This attribute, when set to true, ensures that the multiple cores pointing to the same Schema resource file will be referring to the same IndexSchema Object. Sharing the IndexSchema Object makes loading the core faster. If you use this feature, make sure that no core-specific property is used in your Schema file.

transientCacheSize

Optional

Default: none

Defines how many cores with transient=true that can be loaded before swapping the least recently used core for a new core.

configSetBaseDir

Optional

Default: $SOLR_HOME/configsets

The directory under which configsets for Solr cores can be found.

maxBooleanClauses

Optional

Default: see description

Sets the maximum number of (nested) clauses allowed in any query.

This global limit provides a safety constraint on the total number of clauses allowed in any query against any collection — regardless of whether those clauses were explicitly specified in a query string, or were the result of query expansion/re-writing from a more complex type of query based on the terms in the index. This limit is enforced at multiple points in Lucene, both to prevent primitive query objects (mainly BooleanQuery) from being constructed with an excessive number of clauses in a way that may exhaust the JVM heap, but also to ensure that no composite query (made up of multiple primitive queries) can be executed with an excessive total number of nested clauses in a way that may cause a search thread to use excessive CPU.

In default configurations this property uses the value of the solr.max.booleanClauses system property if specified. This is the same system property used in the _default configset for the <maxBooleanClauses> element of solrconfig.xml making it easy for Solr administrators to increase both values (in all collections) without needing to search through and update all of their configs.

<maxBooleanClauses>${solr.max.booleanClauses:1024}</maxBooleanClauses>

The <solrcloud> Element

This element defines several parameters that relate so SolrCloud. This section is ignored unless theSolr instance is started with either -DzkRun or -DzkHost

distribUpdateConnTimeout

Optional

Default: none

Used to set the underlying connTimeout for intra-cluster updates.

distribUpdateSoTimeout

Optional

Default: none

Used to set the underlying socketTimeout for intra-cluster updates.

host

Optional

Default: none

The hostname Solr uses to access cores.

hostContext

Optional

Default: none

The url context path.

hostPort

Optional

Default: ${solr.port.advertise:0}

The port Solr uses to access cores, and advertise Solr node locations through liveNodes. This option is only necessary if a Solr instance is listening on a different port than it wants other nodes to contact it at. For example, if the Solr node is running behind a proxy or in a cloud environment that allows for port mapping, such as Kubernetes. hostPort is the port that the Solr instance wants other nodes to contact it at.

In the default solr.xml file, this is set to ${solr.port.advertise:0}. If no port is passed via the solr.xml (i.e., 0), then Solr will default to the port that jetty is listening on, defined by ${jetty.port}.

leaderVoteWait

Optional

Default: none

When SolrCloud is starting up, how long each Solr node will wait for all known replicas for that shard to be found before assuming that any nodes that haven’t reported are down.

leaderConflictResolveWait

Optional

Default: 180000 milliseconds

When trying to elect a leader for a shard, this property sets the maximum time a replica will wait to see conflicting state information to be resolved; temporary conflicts in state information can occur when doing rolling restarts, especially when the node hosting the Overseer is restarted.

Typically, the default value of 180000 (ms) is sufficient for conflicts to be resolved; you may need to increase this value if you have hundreds or thousands of small collections in SolrCloud.

zkClientTimeout

Optional

Default: none

A timeout for connection to a ZooKeeper server. It is used with SolrCloud.

zkHost

Optional

Default: none

In SolrCloud mode, the URL of the ZooKeeper host that Solr should use for cluster state information.

genericCoreNodeNames

Optional

Default: none

If true, node names are not based on the address of the node, but on a generic name that identifies the core. When a different machine takes over serving that core things will be much easier to understand.

zkCredentialsProvider & zkACLProvider

Optional

Default: none

Optional parameters that can be specified if you are using ZooKeeper Access Control.

distributedClusterStateUpdates

Optional

Default: none

If true, the internal behavior of SolrCloud is changed to not use the Overseer for collections' state.json updates but do this directly against ZooKeeper.

The <logging> Element

class

Optional

Default: none

The class to use for logging. The corresponding JAR file must be available to Solr, perhaps through a <lib> directive in solrconfig.xml.

enabled

Optional

Default: true

Whether to enable logging or not.

The <logging><watcher> Element

size

Optional

Default: 50

The number of log events that are buffered.

threshold

Optional

Default: none

The logging level above which your particular logging implementation will record. For example when using Log4j one might specify DEBUG, WARN, INFO, etc.

The <shardHandlerFactory> Element

Custom shard handlers can be defined in solr.xml if you wish to create a custom shard handler.

<shardHandlerFactory name="ShardHandlerFactory" class="qualified.class.name">

Since this is a custom shard handler, sub-elements are specific to the implementation. The default and only shard handler provided by Solr is the HttpShardHandlerFactory in which case, the following sub-elements can be specified:

socketTimeout

Optional

Default: see description

The read timeout for intra-cluster query and administrative requests. The default is the same as the distribUpdateSoTimeout specified in the <solrcloud> section.

connTimeout

Optional

Default: see description

The connection timeout for intra-cluster query and administrative requests. Defaults to the distribUpdateConnTimeout specified in the <solrcloud> section.

urlScheme

Optional

Default: none

The URL scheme to be used in distributed search.

maxConnectionsPerHost

Optional

Default: 100000

Maximum connections allowed per host.

corePoolSize

Optional

Default: 0

The initial core size of the threadpool servicing requests.

maximumPoolSize

Optional

Default: none

The maximum size of the threadpool servicing requests. Default is unlimited.

maxThreadIdleTime

Optional

Default: 5 seconds

The amount of time in seconds that idle threads persist for in the queue, before being killed.

sizeOfQueue

Optional

Default: none

If the threadpool uses a backing queue, what is its maximum size to use direct handoff. Default is to use a SynchronousQueue.

fairnessPolicy

Optional

Default: false

A boolean to configure if the threadpool favors fairness over throughput.

replicaRouting

Optional

Default: see description

A NamedList specifying replica routing preference configuration. This may be used to select and configure replica routing preferences. default=true may be used to set the default base replica routing preference. Only positive default status assertions are respected; i.e., default=false has no effect. If no explicit default base replica routing preference is configured, the implicit default will be random.

<shardHandlerFactory class="HttpShardHandlerFactory">
  <lst name="replicaRouting">
    <lst name="stable">
      <bool name="default">true</bool>
      <str name="dividend">routingDividend</str>
      <str name="hash">q</str>
    </lst>
  </lst>
</shardHandlerFactory>

Replica routing may also be specified (overriding defaults) per-request, via the shards.preference request parameter. If a request contains both dividend and hash, dividend takes priority for routing. For configuring stable routing, the hash parameter implicitly defaults to a hash of the String value of the main query parameter (i.e., q).

+ The dividend parameter must be configured explicitly; there is no implicit default. If only dividend routing is desired, hash may be explicitly set to the empty string, entirely disabling implicit hash-based routing.

The <metrics> Element

The <metrics> element in solr.xml allows you to customize the metrics reported by Solr. You can define system properties that should not be returned, or define custom suppliers and reporters.

If you would like to customize the metrics for your installation, see the Metrics Configuration section.

Substituting JVM System Properties in solr.xml

Solr supports variable substitution of JVM system property values in solr.xml, which allows runtime specification of various configuration options. The syntax is ${propertyname[:option default value]}. This allows defining a default that can be overridden when Solr is launched. If a default value is not specified, then the property must be specified at runtime or the solr.xml file will generate an error when parsed.

Any JVM system properties usually specified using the -D flag when starting the JVM, can be used as variables in the solr.xml file.

For example, in the solr.xml file shown below, the socketTimeout and connTimeout values are each set to "60000". However, if you start Solr using bin/solr -DsocketTimeout=1000, the socketTimeout option of the HttpShardHandlerFactory to be overridden using a value of 1000ms, while the connTimeout option will continue to use the default property value of "60000".

<solr>
  <shardHandlerFactory name="shardHandlerFactory"
                       class="HttpShardHandlerFactory">
    <int name="socketTimeout">${socketTimeout:60000}</int>
    <int name="connTimeout">${connTimeout:60000}</int>
  </shardHandlerFactory>
</solr>