Matheus de Oliveira <matioli.matheus@xxxxxxxxx> writes: > Em 26 de fev de 2016 4:44 PM, "joe meiring" <josephmeiring@xxxxxxxxx> > escreveu: >> The same query for parameters is rather slow and does NOT use the index: >> >> EXPLAIN ANALYZE >> select * >> from parameter >> where exists ( >> select 1 from datavalue >> where datavalue.parameter_id = parameter.id limit 1 >> ); > Please, could you execute both queries without the LIMIT 1 and show us the > plans? > LIMIT in the inner query is like a fence and it caps some optimizations > available for EXISTS, you'd better avoid it and see if you get a proper > semi-join plan then. FWIW, PG >= 9.5 will ignore a LIMIT 1 inside an EXISTS, so that you get the same plan with or without it. But that does act as an optimization fence in earlier releases. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
