Solr Upgrade Notes

The JSON parameter to set cluster-wide default cluster properties with the CLUSTERPROP command has changed.

The old syntax nested the defaults into a property named clusterDefaults. The new syntax uses only defaults. The command to use is still set-obj-property.

An example of the new syntax is:

{
  "set-obj-property": {
    "defaults" : {
      "collection": {
        "numShards": 2,
        "nrtReplicas": 1,
        "tlogReplicas": 1,
        "pullReplicas": 1
      }
    }
  }
}

The old syntax will be supported until at least Solr 9, but users are advised to begin using the new syntax as soon as possible.

An autoscaling policy is now used as the default strategy for selecting nodes on which new replicas or replicas of new collections are created.

A default policy is now in place for all users, which will sort nodes by the number of cores and available freedisk, which means by default a node with the fewest number of cores already on it and the highest available freedisk will be selected for new core creation.

1. It removes the restriction against using maxShardsPerNode when an autoscaling policy is in place. This parameter can now always be set when creating a collection.

2. It removes the default setting of maxShardsPerNode=1 when an autoscaling policy is in place. It will be set correctly (if required) regardless of whether an autoscaling policy is in place or not.

   The default value of maxShardsPerNode is still 1. It can be set to -1 if the old behavior of unlimited maxSharedsPerNode is desired.

Lucene has introduced the ByteBuffersDirectoryFactory as a replacement for the RAMDirectoryFactory, which will be removed in Solr 9.

While most users are still encouraged to use the NRTCachingDirectoryFactory, which allows Lucene to select the best directory factory to use, if you have explicitly configured Solr to use the RAMDirectoryFactory, you are encouraged to switch to the new implementation as soon as possible before Solr 9 is released.

For more information about the new directory factory, see the Jira issue LUCENE-8438.

For more information about the directory factory configuration in Solr, see the section DataDir and DirectoryFactory in SolrConfig.

When using the TieredMergePolicy, the default merge policy for Solr, optimize and expungeDeletes now respect the maxMergedSegmentMB configuration parameter, which defaults to 5000 (5GB).

If it is absolutely necessary to control the number of segments present after optimize, specify maxSegments as a positive integer. Setting maxSegments higher than 1 are honored on a "best effort" basis.

The TieredMergePolicy will also reclaim resources from segments that exceed maxMergedSegmentMB more aggressively than earlier.

The old Leader-In-Recovery implementation (implemented in Solr 4.9) is now deprecated and replaced. Solr will support rolling upgrades from old 7.x versions of Solr to future 7.x releases until the last release of the 7.x major version.

This means to upgrade to Solr 8 in the future, you will need to be on Solr 7.3 or higher.

Starting a query string with local parameters {!myparser …​} is used to switch from one query parser to another, and is intended for use by Solr system developers, not end users doing searches. To reduce negative side-effects of unintended hack-ability, Solr now limits the cases when local parameters will be parsed to only contexts in which the default parser is "lucene" or "func".

So, if defType=edismax then q={!myparser …​} won’t work. In that example, put the desired query parser into the defType parameter.

Another example is if deftype=edismax then hl.q={!myparser …​} won’t work for the same reason. In this example, either put the desired query parser into the hl.qparser parameter or set hl.qparser=lucene. Most users won’t run into these cases but some will need to change.

If you must have full backwards compatibility, use luceneMatchVersion=7.1.0 or an earlier version.

The eDisMax parser by default no longer allows subqueries that specify a Solr parser using either local parameters, or the older _query_ magic field trick.

For example, {!prefix f=myfield v=enterp} or _query_:"{!prefix f=myfield v=enterp}" are not supported by default any longer. If you want to allow power-users to do this, set uf=* query or some other value that includes _query_.

If you need full backwards compatibility for the time being, use luceneMatchVersion=7.1.0 or something earlier.

The feature to automatically add replicas if a replica goes down, previously available only when storing indexes in HDFS, has been ported to the autoscaling framework. Due to this, autoAddReplicas is now available to all users even if their indexes are on local disks.

Existing users of this feature should not have to change anything. However, they should note these changes:

• Behavior: Changing the autoAddReplicas property from disabled (false) to enabled (true) using MODIFYCOLLECTION API no longer replaces down replicas for the collection immediately. Instead, replicas are only added if a node containing them went down while autoAddReplicas was enabled. The parameters autoReplicaFailoverBadNodeExpiration and autoReplicaFailoverWorkLoopDelay are no longer used.

• Deprecations: Enabling/disabling autoAddReplicas cluster-wide with the API will be deprecated; use suspend/resume trigger APIs with name=".auto_add_replicas" instead.

  More information about the changes to this feature can be found in the section SolrCloud Automatically Adding Replicas.

• If a reporter configures the group="shard" attribute then please also configure the class="org.apache.solr.metrics.reporters.solr.SolrShardReporter" attribute.

• If a reporter configures the group="cluster" attribute then please also configure the class="org.apache.solr.metrics.reporters.solr.SolrClusterReporter" attribute.

  See the section Shard and Cluster Reporters for more information.