谢谢，Gerhard！非常感谢你的帮助。这个问题变得越来越奇怪了。
对我来说，incoming_referers 出问题也说不通。我最近一次从生产环境恢复到这个测试站点是在 10 月。
看起来问题出在数据库或索引上。我怀疑是某个插件导致的，但错误涉及这么多不同的索引，不太可能是单个插件造成的。之前用 grep 在插件中搜索与损坏索引相关的问题，结果一无所获。
有一次恢复时，我得到了以下错误：
[2020-01-03 16:25:30] ERROR: could not create unique index "index_plugin_store_rows_on_plugin_name_and_key"
我执行了：
[10] pry(main)> PluginStoreRow.where(plugin_name: 'discourse-data-explorer',key: 'q:-8').destroy_all
然后再次尝试：
[2020-01-03 16:49:16] ERROR: could not create unique index "index_tags_on_lower_name"
[2020-01-03 16:49:16] DETAIL: Key (lower(name::text))=(addins) is duplicated.
以下是最新恢复过程的完整头部日志：
[2020-01-03 16:41:34] 'pfaffman' has started the restore!
[2020-01-03 16:41:34] Marking restore as running...
[2020-01-03 16:41:34] Making sure /var/www/discourse/tmp/restores/default/2020-01-03-164133 exists...
[2020-01-03 16:41:34] Downloading archive to tmp directory...
[2020-01-03 16:45:20] No metadata file to extract.
[2020-01-03 16:45:20] Validating metadata...
[2020-01-03 16:45:20] Current version: 20191220134101
[2020-01-03 16:45:20] Restored version: 20191129144706
[2020-01-03 16:45:20] Extracting dump file...
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:15] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] CREATE INDEX
[2020-01-03 16:49:16] ERROR: could not create unique index "index_tags_on_lower_name"
[2020-01-03 16:49:16] DETAIL: Key (lower(name::text))=(addins) is duplicated.
[2020-01-03 16:49:16] ERROR: current transaction is aborted, commands ignored until end of transaction block
[2020-01-03 16:49:16] ERROR: current transaction is aborted, commands ignored until end of transaction block
[2020-01-03 16:49:16] ERROR: current transaction is aborted, commands ignored until end of transaction block