A possible performance regression was introduced in 8.6 release. https://issues.apache.org/jira/browse/SOLR-14656?focusedCommentId=17160311&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-17160311
Andrzej mentioned in Slack he can do a bugfix release, but that he's on vacation until 27.07. Would appreciate if someone can cross verify and revert/release 8.6.1 if needed. Thanks, Ishan
