When I was running extensions/GrowthExperiments/maintenance/migrateMentorMenteeRelationship.php for cswiki, @Marostegui notified me that "we are getting a bunch of Wikimedia\Rdbms\Database::normalizeUpsertKeys called with deprecated parameter style: the unique key array should be a string or array of string arrays errors".
from /srv/mediawiki/php-1.37.0-wmf.1/includes/libs/rdbms/database/Database.php(2245)
#0 /srv/mediawiki/php-1.37.0-wmf.1/includes/libs/rdbms/database/Database.php(3408): Wikimedia\Rdbms\Database->normalizeUpsertKeys(array)
#1 /srv/mediawiki/php-1.37.0-wmf.1/includes/libs/rdbms/database/DBConnRef.php(68): Wikimedia\Rdbms\Database->upsert(string, array, array, array, string)
#2 /srv/mediawiki/php-1.37.0-wmf.1/includes/libs/rdbms/database/DBConnRef.php(504): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#3 /srv/mediawiki/php-1.37.0-wmf.1/extensions/GrowthExperiments/includes/Mentorship/Store/DatabaseMentorStore.php(105): Wikimedia\Rdbms\DBConnRef->upsert(string, array, array, array, string)
#4 /srv/mediawiki/php-1.37.0-wmf.1/extensions/GrowthExperiments/includes/Mentorship/Store/DatabaseMentorStore.php(121): GrowthExperiments\Mentorship\Store\DatabaseMentorStore->setMentorForUserReal(User, User, string)
#5 /srv/mediawiki/php-1.37.0-wmf.1/extensions/GrowthExperiments/includes/Mentorship/Store/MentorStore.php(149): GrowthExperiments\Mentorship\Store\DatabaseMentorStore->setMentorForUserInternal(User, User, string)
#6 /srv/mediawiki/php-1.37.0-wmf.1/extensions/GrowthExperiments/includes/Mentorship/Store/SetUserMentorDatabaseJob.php(47): GrowthExperiments\Mentorship\Store\MentorStore->setMentorForUser(User, User, string)
#7 /srv/mediawiki/php-1.37.0-wmf.1/extensions/EventBus/includes/JobExecutor.php(79): GrowthExperiments\Mentorship\Store\SetUserMentorDatabaseJob->run()
#8 /srv/mediawiki/rpc/RunSingleJob.php(76): MediaWiki\Extension\EventBus\JobExecutor->execute(array)
#9 {main}Logstash link: https://logstash.wikimedia.org/goto/004b938dedef4a372378b6b3460c78c7