Re: OFFSET/LIMIT - Disparate Performance w/ Go application

Matt Silverlock <matt@eatsleeprepeat.net> writes:
> Hi all. This might be tricky in so much as there’s a few moving parts (when isn’t there?), but I’ve tried to test the
postgresside as much as possible. 
> Trying to work out a potential database bottleneck with a HTTP application (written in Go):
> Pages that render HTML templates but don’t perform DB queries can hit ~36k+ req/s
> Pages that perform a SELECT on a single row net about ~6.6k req/s: db.Get(l, "SELECT * FROM listings WHERE id = $1
ANDexpiry_date > current_date", l.Id) 
> Pages that SELECT multiple rows with OFFSET and LIMIT conditions struggle to top 1.3k req/s

You don't show us exactly what you're doing with OFFSET/LIMIT, but I'm
going to guess that you're using it to paginate large query results.
That's basically always going to suck: Postgres has no way to implement
OFFSET except to generate and then throw away that number of initial rows.
If you do the same query over again N times with different OFFSETs, it's
going to cost you N times as much as the base query would.

If the application's interaction with the database is stateless then you
may not have much choice, but if you do have a choice I'd suggest doing
pagination by means of fetching from a cursor rather than independent
queries.

            regards, tom lane