Re: Same query taking less time in low configuration machine

HI,

OS cache is updated and I had run the query few times with almost the same
result each time.

Regards,
Vishwa

On Tue, Jul 14, 2020 at 6:16 PM Philip Semanchuk <
philip(at)americanefficient(dot)com> wrote:

>
>
> > On Jul 14, 2020, at 5:27 AM, Vishwa Kalyankar <
> vishwakalyankar8(at)gmail(dot)com> wrote:
> >
> > Hi,
> >
> > I have two machines - one with 8GB RAM & 4core CPU and the other with
> 64GB Ram & 24 core CPU. Both machines have the same DB (Postgres 12 +
> Postgis 2.5.3). Same query is taking less time in low end machine whereas
> more time in high end machine. Any thoughts on where to look? I have
> tuned the db in both machines according to https://pgtune.leopard.in.ua/#/
> >
> >
> > Below I am pasting the output of query explain in both the machines.
> >
> > -bash-4.2$ psql -p 5434
> > psql (12.3)
> > Type "help" for help.
> >
> > postgres=# \c IPDS_KSEB;
> > You are now connected to database "IPDS_KSEB" as user "postgres".
> > IPDS_KSEB=# explain analyze select * from
> kseb_geometry_trace_with_barrier_partition(5,'kottarakara_version',437,'htline',2)
> ;
> >
> QUERY PLAN
> >
> ---------------------------------------------------------------------------------------------------------------------------------------------------------
> > Function Scan on kseb_geometry_trace_with_barrier_partition
> (cost=0.25..10.25 rows=1000 width=169) (actual time=11626.548..11626.568
> rows=254 loops=1)
> > Planning Time: 0.212 ms
> > Execution Time: 11628.590 ms
> >
> >
> > -bash-4.2$ psql -p 5422
> > psql (12.3)
> > Type "help" for help.
> >
> > postgres=# \c IPDS_KSEB;
> > You are now connected to database "IPDS_KSEB" as user "postgres".
> > IPDS_KSEB=# explain analyze select * from
> kseb_geometry_trace_with_barrier_partition(5,'kottarakara_version',437,'htline',2)
> ;
> >
> QUERY PLAN
> >
> ---------------------------------------------------------------------------------------------------------------------------------------------------------
> > Function Scan on kseb_geometry_trace_with_barrier_partition
> (cost=0.25..10.25 rows=1000 width=169) (actual time=22304.425..22304.448
> rows=254 loops=1)
> > Planning Time: 0.219 ms
> > Execution Time: 22352.219 ms
> > (3 rows)
> >
>
> Hi Vishwa,
> Is it possible that your data is in the cache on the low end machine but
> not on the high end machine? There’s both the Postgres cache and the OS
> disk cache to consider. You can see what’s in the Postgres cache with an
> extension like pg_buffercache. I don’t know of a way to see what’s in the
> OS cache; maybe others do.
>
> Cheers
> Philip
>
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>