2017-02-16 13:25 GMT+13:00 Steve Atkins <st...@blighty.com>: > > > On Feb 15, 2017, at 3:58 PM, Patrick B <patrickbake...@gmail.com> wrote: > > > > Hi all, > > > > I just got a quick question about warm-cache. I'm using PG 9.2. > > > > When I execute this statement soon after I start/restart the database: > > > > explain select id from test where id = 124; > > > > The runtime is 40ms. > > > > Then, If I execute this statement just after the above one; > > > > explain analyze select id from test where id = 124; > > > > The runtime is 0.8ms. > > This doesn't make seem to make sense. > > "explain select ..." doesn't run the query. All it shows is the plan the > planner chose and some estimates of the "cost" of different steps, with no > time. Where are you getting 40ms from in this case? >
>From my DB-VISUALIZER - it shows how long the query took. > > "explain analyze select ..." does run the query, along with some - > potentially non-trivial - instrumentation to measure each step of the plan, > so you can see whether the planner estimates are reasonable or wildly off. > > > Well.. that is what's happening. For the first time I ran the query, it took >10 seconds. Now it is taking less than a second. How can I clear for good the cache? So i can have a real idea of how long the query takes to run?
