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https://solr.apache.org/guide/solr/9_0/upgrade-notes/solr-upgrade-notes.html <--- FIX LINK

Solr 9.0.0 Release Highlights:

  • Minimum Java version supported: Java 11

  • Powered by Lucene 9.0, with numerous small and large improvements, such as smaller index footprint.

Querying and Indexing

  • Dense Vector "Neural" Search through DenseVectorField fieldType and K-Nearest-Neighbor (KNN) Query Parser.
  • Admin UI support for SQL Querying.
  • New snowball stemmers: Hindi, Indonesian, Nepali, Serbian, Tamil, and Yiddish.
  • New NorwegianNormalizationFilter.

Security

  • Certificate Authentication Plugin , enabling that enables end-to-end use of x509 client certificates for Authentication and Authorization.
  • Improved security when using PKI Authentication plugin.
  • Upgrade to Zookeeper 3.7, allowing for TLS protected ZK communication.
  • All request handlers support security permissions for access.
  • Ability to disable admin UI through a system property.
  • The property blockUnknown in the BasicAuthPlugin and the JWTAuthPlugin now defaults to true instead of false.
  • Solr now runs with the Java security manager enabled by default. Hadoop users may need to disable this.
  • Solr embedded zookeeper only binds to localhost by default. See Upgrade Notes for how to obtain old behavior.
  • Dependency updates - A lot of dependency updates make Solr overall much more secure.

Stability and Scalability

  • Rate limiting provides a way to throttle update and search requests based on usage metrics.
  • Task management interface allows declaring tasks as cancellable and trackable.
  • Ability to specify node roles in Solr. This release supports 'Overseer' and 'Data' roles out of the box.
  • New API for pluggable replica assignment implementations that replaces the auto-scaling framework.
  • Support for distributed processing of cluster state updates and collection API calls , without relying on the Overseer.

Build and Docker

  • Solr is now built and released independently from of Apache Lucene (separate Apache projects).
  • Build system switched to Gradle , no longer uses from Ant + Ivy.
  • Docker image creation is now a part of the Apache Solr Github repo.
  • Docker image documentation is now a part of the reference guide.
  • Official Docker image upgraded to use JDK17 (by Eclipse Temurin) and ability to create a local image that is functionally identical local imageto the official one.

Other

  • Contrib modules are now just "modules". You can easily enable module(s) through environment variable SOLR_MODULES.
  • Features lifted out as separate modules are: HDFS, Hadoop-Auth, SQL, Scripting, and JWT-Auth.
  • The "dist" folder in the release is gone. Module jars are now inside respective module's lib/ folder.
  • Metrics handler only depends on SolrJ instead of core and has its own log4j2.xml now so it doesn’t share Solr’s logging config.
  • SolrJ class CloudSolrClient now supports HTTP2. It has a new Builder. See CloudLegacySolrClient for the 8.x version of this class
  • Jetty Request log is now enabled by default, i.e. logging every request.

Deprecations and Removals

  • The Data Import Handler (DIH) is an independent project now; it is no longer a part of Solr.
  • No more support for clusterstate.json and MIGRATESTATE API has been removed. If your collections use clusterstate.json, please refer to the Upgrade Notes.
  • Auto scaling framework has been removed. Please refer to replica placement plugins for alternate options.
  • LegacyBM25SimilarityFactory has been removed.
  • VelocityResponseWriter is an independent project now; it is no longer a part of Solr. This encompasses all previously included /browse and wt=velocity examples.
  • Legacy SolrCache implementations (LRUCache, LFUCache, FastLRUCache) have been removed. Users should modify their existing configurations to use CaffeineCache instead.
  • Cross Data Center Replication has been removed
  • SolrJ clients like HttpSolrClient and LBHttpSolrClient that lacked HTTP2 support have been deprecated. The old CloudSolrClient has been renamed as CloudLegacySolrClient and deprecated.
  • SimpleFSDirectoryFactory is removed in favor of NIOFSDirectoryFactory.