From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Matt Silverlock <matt(at)eatsleeprepeat(dot)net> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: OFFSET/LIMIT - Disparate Performance w/ Go application |
Date: | 2014-06-12 14:58:06 |
Message-ID: | 24297.1402585086@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Matt Silverlock <matt(at)eatsleeprepeat(dot)net> writes:
> Hi all. This might be tricky in so much as theres a few moving parts (when isnt there?), but Ive tried to test the postgres side 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 dont 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 AND expiry_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
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