= Solr Upgrade Notes
:page-children: major-changes-in-solr-8, major-changes-in-solr-7, major-changes-from-solr-5-to-solr-6
:page-toclevels: 3
:page-tocclass: right
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

The following notes describe changes to Solr in recent releases that you should be aware of before upgrading.

These notes highlight the biggest changes that may impact the largest number of implementations. It is not a comprehensive list of all changes to Solr in any release.

When planning your Solr upgrade, consider the customizations you have made to your system and review the {solr-javadocs}/changes/Changes.html[`CHANGES.txt`] file found in your Solr package. That file includes all the changes and updates that may effect your existing implementation.

Detailed steps for upgrading a Solr cluster are in the section <<upgrading-a-solr-cluster.adoc#upgrading-a-solr-cluster,Upgrading a Solr Cluster>>.

== Upgrading to 8.x Releases

If you are upgrading from 7.x, see the section <<Upgrading from 7.x Releases>> below.

=== Solr 8.1

See the https://wiki.apache.org/solr/ReleaseNote810[8.1 Release Notes] for an overview of the main new features of Solr 8.1.

When upgrading to 8.1.x, users should be aware of the following major changes from v8.0.

*Global maxBooleanClauses Parameter*

* The behavior of the `maxBooleanClauses` parameter has changed to reduce the risk of exponential query expansion when dealing with pathological query strings.
+
A default upper limit of 1024 clauses is now enforced at the node level. This was the default prior to 7.0, and it can be overridden with a new global parameter in `solr.xml`. This limit will be enforced for all queries whether explicitly defined by the user (or client), or created by Solr and Lucene internals.
+
An identical parameter is available in `solrconfig.xml` for limiting the size of queries explicitly defined by the user (or client), but this per-collection limit will still be restricted by the global limit set in `solr.xml`.
+
If your use case demands that you a lot of OR or AND clauses in your queries, upon upgrade to 8.1 you may need to adjust the global `maxBooleanClauses` parameter since between 7.0 and 8.1 the limit was effectively unbounded.
+
For more information about the new parameter, see the section <<format-of-solr-xml.adoc#global-maxbooleanclauses,Format of solr.xml: maxBooleanClauses>>.

*Security*

* JSON Web Tokens (JWT) are now supported for authentication. These allow Solr to assert a user is already authenticated via an external identity provider, such as an OpenID Connect-enabled IdP. For more information, see the section <<jwt-authentication-plugin.adoc#jwt-authentication-plugin,JWT Authentication Plugin>>.

* A new security plugin for audit logging has been added. A default class `SolrLogAuditLoggerPlugin` is available and configurable in `security.json`. The base class is also extendable for adding custom audit plugins if needed. See the section <<audit-logging.adoc#audit-logging,Audit Logging>> for more information.

*Collections API*

* The output of the REQUESTSTATUS command in the Collections API will now include internal asynchronous requests (if any) in the "success" or "failed" keys.

* The CREATE command will now return the appropriate status code (4xx, 5xx, etc.) when the command has failed. Previously, it always returned `0`, even in failure.

* The MODIFYCOLLECTION command now accepts an attribute to set a collection as read-only. This can be used to block a collection from receiving any updates while still allowing queries to be served. See the section <<collections-api.adoc#modifycollection,MODIFYCOLLECTION>> for details on how to use it.

* A new command RENAME allows renaming a collection by setting up a one-to-one alias using the new name. For more information, see the section <<collections-api.adoc#rename,RENAME>>.

* A new command REINDEXCOLLECTION allows indexing existing stored fields from a source collection into a new collection. For more information, please see the section <<collections-api.adoc#reindexcollection,REINDEXCOLLECTION>>.

*Logging*

* The default Log4j2 logging mode has been changed from synchronous to asynchronous. This will improve logging throughput and reduce system contention at the cost of a _slight_ chance that some logging messages may be missed in the event of abnormal Solr termination.
+
If even this slight risk is unacceptable, the Log4j configuration file found in `server/resources/log4j2.xml` has the synchronous logging configuration in a commented section and can be edited to re-enable synchronous logging.

*Metrics*

* The SolrGangliaReporter has been removed from Solr. The metrics library used by Solr, Dropwizard Metrics, was updated to version 4, and Ganglia support was removed from it due to a dependency on the LGPL license.

*Browse UI (Velocity)*

* Velocity and Velocity Tools were both upgraded as part of this release. Velocity upgraded from 1.7 to 2.0. Please see https://velocity.apache.org/engine/2.0/upgrading.html about upgrading. Velocity Tools upgraded from 2.0 to 3.0. For more details, please see https://velocity.apache.org/tools/3.0/upgrading.html for details about the upgrade.

*Default Garbage Collector (GC)*

* Solr's default GC has been changed from CMS to G1. If you prefer to use CMS or any other GC method, you can modify the `GC_TUNE` section of `solr.in.sh` (*nix) or `solr.in.cmd` (Windows).


== Upgrading from 7.x Releases

The upgrade from 7.x to Solr 8.0 introduces several major changes that you should be aware of before upgrading.
These changes are described in the section <<major-changes-in-solr-8.adoc#major-changes-in-solr-8,Major Changes in Solr 8>>. It's strongly recommended that you do a thorough review of that section before starting your upgrade.

[NOTE]
If you run in SolrCloud mode, you must be on Solr version 7.3 or higher in order to upgrade to 8.x.

== Upgrading from Pre-7.x Versions

Users upgrading from versions of Solr prior to 7.x are strongly encouraged to consult {solr-javadocs}/changes/Changes.html[`CHANGES.txt`] for the details of _all_ changes since the version they are upgrading from.

The upgrade from Solr 6.x to Solr 7.0 introduced several *major* changes that you should be aware of before upgrading. Please do a thorough review of the section <<major-changes-in-solr-7.adoc#major-changes-in-solr-7,Major Changes in Solr 7>> before starting your upgrade.

A summary of the significant changes between Solr 5.x and Solr 6.0 is in the section <<major-changes-from-solr-5-to-solr-6.adoc#major-changes-from-solr-5-to-solr-6,Major Changes from Solr 5 to Solr 6>>.
