https://logstash.wikimedia.org/#/dashboard/elasticsearch/mediawiki-error – search for "Search backend error during". As of July 2018, about 11,000 recorded instances of this error per month.
>>! Normalised:
> Search backend error during {queryType} search for '{query}' after {tookMs}: {error_message}
```name=Sample (1.32.0.wmf-14)
Search backend error during comp_suggest search for 'audit' after 1: :
elasticTookMs: "0"
error_message: ":"
hitsOffset: "0"
hitsReturned: "0"
hitsTotal: "-"
level:WARNING
channel:CirrusSearch
url: /w/api.php?action=opensearch&search=audit&limit=15
reqId: W2CfuApAEMIAADlGDK8AAAAK
```
```name=Sample (1.25wmf23)
Warning: Search backend error during degraded_full_text search
for '"nicht antretbar*" OR "nicht antreten*" OR "nicht erstattbar*" OR "nicht erstatten*" OR "nicht erstattet*" OR "nicht stornierbar*" OR "nicht stornieren*" OR "nicht storniert*"'
after 62.
Parse error on ' or OR OR OR OR OR or ': Encountered " <OR> "OR "" at line 1, column 11.
[Called from CirrusSearch\ElasticsearchIntermediary::failure in /srv/mediawiki/php-1.25wmf23/extensions/CirrusSearch/includes/ElasticsearchIntermediary.php at line 98] in /srv/mediawiki/php-1.25wmf23/includes/debug/MWDebug.php on line 300
```