The queries produced in Wikibase\Repo\Store\Sql\SqlEntityIdPager::fetchIds is slow.
It runs queries like:
SELECT /* Wikibase\Repo\Store\Sql\SqlEntityIdPager::fetchIds datasets@snapsh... */ page_id,page_title FROM `page` WHERE (page_id > 3128073) AND page_namespace IN ('0','120') AND page_is_redirect = '0' ORDER BY page_id ASC LIMIT 100
(takes >1s on db1082)
… rewriting the queries as follows makes it way faster for me:
SELECT /* Wikibase\Repo\Store\Sql\SqlEntityIdPager::fetchIds datasets@snapsh... */ page_id,page_title,page_is_redirect FROM `page` WHERE (page_id > 3128073) AND page_namespace IN ('0','120') HAVING page_is_redirect = 0 ORDER BY page_id ASC LIMIT 100;
(takes <0.00s on db1082)