Re: OFFSET/LIMIT - Disparate Performance w/ Go application - Mailing list pgsql-performance
På torsdag 12. juni 2014 kl. 16:58:06, skrev Tom Lane <tgl@sss.pgh.pa.us>:
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 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 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 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.
Are there any plans to make PG implement OFFSET more efficiently, so it doesn't have to "read and throw away"?
I used SQL Server back in 2011 in a project and seem to remember they implemented offset pretty fast. Paging in a resultset of millions was much faster than in PG.
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Andreas Jospeh Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
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