While trying to test T238043 with a script, I end up with this:
...
14200 (11.52 pages/sec 11.52 revs/sec)> ] 22% ETA 1:12:18
14300 (11.52 pages/sec 11.52 revs/sec)> ] 22% ETA 1:12:11
14400 (11.52 pages/sec 11.52 revs/sec)> ] 22% ETA 1:11:58
CannotCreateActorException from line 2282 of /opt/htdocs/mediawiki/includes/user/User.php: Cannot create an actor for a usable name that is not an existing user
#0 /opt/htdocs/mediawiki/includes/ActorMigration.php(303): User->getActorId(Object(Wikimedia\Rdbms\DatabaseMysqli))
#1 /opt/htdocs/mediawiki/includes/Revision/RevisionStore.php(753): ActorMigration->getInsertValuesWithTempTable(Object(Wikimedia\Rdbms\DatabaseMysqli), 'rev_user', Object(User))
#2 /opt/htdocs/mediawiki/includes/Revision/RevisionStore.php(552): MediaWiki\Revision\RevisionStore->insertRevisionRowOn(Object(Wikimedia\Rdbms\DatabaseMysqli), Object(MediaWiki\Revision\MutableRevisionRecord), Object(Title), 0)
#3 /opt/htdocs/mediawiki/includes/Revision/RevisionStore.php(490): MediaWiki\Revision\RevisionStore->insertRevisionInternal(Object(MediaWiki\Revision\MutableRevisionRecord), Object(Wikimedia\Rdbms\DatabaseMysqli), Object(User), Object(CommentStoreComment), Object(Title), 14467, 0)
#4 /opt/htdocs/mediawiki/includes/libs/rdbms/database/Database.php(3966): MediaWiki\Revision\RevisionStore->MediaWiki\Revision\{closure}(Object(Wikimedia\Rdbms\DatabaseMysqli), 'MediaWiki\\Revis...')
#5 /opt/htdocs/mediawiki/includes/libs/rdbms/database/DBConnRef.php(68): Wikimedia\Rdbms\Database->doAtomicSection('MediaWiki\\Revis...', Object(Closure))
#6 /opt/htdocs/mediawiki/includes/libs/rdbms/database/DBConnRef.php(635): Wikimedia\Rdbms\DBConnRef->__call('doAtomicSection', Array)
#7 /opt/htdocs/mediawiki/includes/Revision/RevisionStore.php(498): Wikimedia\Rdbms\DBConnRef->doAtomicSection('MediaWiki\\Revis...', Object(Closure))
#8 /opt/htdocs/mediawiki/includes/Revision.php(968): MediaWiki\Revision\RevisionStore->insertRevisionOn(Object(MediaWiki\Revision\MutableRevisionRecord), Object(Wikimedia\Rdbms\DBConnRef))
#9 /opt/htdocs/mediawiki/includes/import/ImportableOldRevisionImporter.php(129): Revision->insertOn(Object(Wikimedia\Rdbms\DBConnRef))
#10 /opt/htdocs/mediawiki/includes/import/WikiRevision.php(616): ImportableOldRevisionImporter->import(Object(WikiRevision))
#11 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(366): WikiRevision->importOldRevision()
#12 /opt/htdocs/mediawiki/maintenance/importDump.php(209): WikiImporter->importRevision(Object(WikiRevision))
#13 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(501): BackupReader->handleRevision(Object(WikiRevision), Object(WikiImporter))
#14 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(941): WikiImporter->revisionCallback(Object(WikiRevision))
#15 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(860): WikiImporter->processRevision(Array, Array)
#16 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(802): WikiImporter->handleRevision(Array)
#17 /opt/htdocs/mediawiki/includes/import/WikiImporter.php(606): WikiImporter->handlePage()
#18 /opt/htdocs/mediawiki/maintenance/importDump.php(359): WikiImporter->doImport()
#19 /opt/htdocs/mediawiki/maintenance/importDump.php(301): BackupReader->importFromHandle(Resource id #252)
#20 /opt/htdocs/mediawiki/maintenance/importDump.php(129): BackupReader->importFromStdin()
#21 /opt/htdocs/mediawiki/maintenance/doMaintenance.php(99): BackupReader->execute()
#22 /opt/htdocs/mediawiki/maintenance/importDump.php(364): require_once('/opt/htdocs/med...')
#23 {main}
[f2e33a53a89f4bbd09627f75] [no req] Wikimedia\Rdbms\DBTransactionError from line 1680 of /opt/htdocs/mediawiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php: BackupReader: Commit failed on server(s) localhost: Cannot execute query from BackupReader while transaction status is ERROR
Backtrace:
#0 /opt/htdocs/mediawiki/includes/libs/rdbms/lbfactory/LBFactory.php(208): Wikimedia\Rdbms\LoadBalancer->commitMasterChanges(string, integer)
#1 /opt/htdocs/mediawiki/includes/libs/rdbms/lbfactory/LBFactorySimple.php(134): Wikimedia\Rdbms\LBFactory->Wikimedia\Rdbms\{closure}(Wikimedia\Rdbms\LoadBalancer, string, array)
#2 /opt/htdocs/mediawiki/includes/libs/rdbms/lbfactory/LBFactory.php(210): Wikimedia\Rdbms\LBFactorySimple->forEachLB(Closure, array)
#3 /opt/htdocs/mediawiki/includes/libs/rdbms/lbfactory/LBFactory.php(273): Wikimedia\Rdbms\LBFactory->forEachLBCallMethod(string, array)
#4 /opt/htdocs/mediawiki/maintenance/doMaintenance.php(124): Wikimedia\Rdbms\LBFactory->commitMasterChanges(string)
#5 /opt/htdocs/mediawiki/maintenance/importDump.php(364): require_once(string)
#6 {main}