On Thu, Jun 12, 2014 at 2:48 PM, Andreas Joseph Krogh <andreas@xxxxxxxxxx> wrote: > > På torsdag 12. juni 2014 kl. 16:58:06, skrev Tom Lane <tgl@xxxxxxxxxxxxx>: > > Matt Silverlock <matt@xxxxxxxxxxxxxxxxxx> 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. I doubt it. Offset is widely regarded as being pretty dubious. SQL has formally defined the way to do this (cursors) and optimizing offset would be complex for such a little benefit. Speaking generally SQL server also has some trick optimizations of other constucts like fast count(*) but in my experience underperforms pg in many areas. merlin
