Re: Hibernate generated query slow compared to 'equivalent' hand written one

Kyle Moser <moser(dot)kyle(at)gmail(dot)com> writes:
> The depesz link for explain (analyze, buffers) is shown below for 3
> different queries. The first two queries show a log dump of the postgres
> log, showing a query that was generated by Java Hibernate. The third query
> was one I wrote and ran in pgadmin that I think is similar to what
> Hibernate is doing.

It's not all that similar: according to the EXPLAIN output, the condition
Hibernate is generating is

Filter: ((FK_USER)::numeric = ANY ('{213,382,131,...,717}'::numeric[]))

whereas your handwritten query is generating

Index Cond: (fk_user = ANY ('{70,150,1248,1269,1530,...,199954}'::bigint[]))

IOW, Hibernate is telling the server that the parameters it's supplying
are NUMERIC not INTEGER, which results in a query using numeric_eq, which
can't be indexed by a bigint index.

If you can't find a hammer big enough to persuade Hibernate that it's
dealing with integers/bigints rather than numerics, you could probably
regain most of the performance by creating an index on (FK_USER::numeric).

BTW, why is one of your EXPLAINs showing the identifiers in upper case
and the other in lower case? One could be forgiven for wondering if
these were really against the same data.

regards, tom lane