PropertySuggester’s SuggestionGenerator directly uses TermSqlIndex::getTopMatchingTerms(), resulting in queries like this (slightly reformatted from T194273#4228564):
SELECT term_entity_type, term_type, term_language, term_text, term_weight, term_full_entity_id FROM `wb_terms` WHERE term_language = 'en' AND (term_text LIKE 'b%' ESCAPE '`') AND term_type IN ('label','alias') AND term_entity_type = 'property' LIMIT 2500
This should use CirrusSearch instead, so that we don’t have to keep expensive indexes on term_text/term_search_key.