Re: Same query taking less time in low configuration machine

Hi Justin,

I am pasting once again the output of low end server , explain result
and shared_buffer size of high end machine.

-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=# set track_io_timing TO on;
SET
IPDS_KSEB=# explain (analyze,buffers, settings) 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=22762.767..22762.800
rows=389 loops=1)
Buffers: shared hit=775445 read=2371
I/O Timings: read=1061.060
Settings: search_path = '"$user", public, topology'
Planning Time: 0.091 ms
Execution Time: 22781.896 ms
(6 rows)

#------------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------

# - Memory -

*shared_buffers = 10GB * # min 128kB
# (change requires restart)
#huge_pages = try # on, off, or try
# (change requires restart)
#temp_buffers = 8MB # min 800kB
#max_prepared_transactions = 0 # zero disables the feature
# (change requires restart)
# Caution: it is not advisable to set max_prepared_transactions nonzero
unless
# you actively intend to use prepared transactions.
work_mem = 10MB # min 64kB
maintenance_work_mem = 2GB # min 1MB
#autovacuum_work_mem = -1 # min 1MB, or -1 to use
maintenance_work_mem
#max_stack_depth = 2MB # min 100kB
#shared_memory_type = mmap # the default is the first option
# supported by the operating system:
# mmap
# sysv
# windows
# (change requires restart)
dynamic_shared_memory_type = posix # the default is the first option
# supported by the operating system:
# posix

On Thu, Jul 16, 2020 at 10:33 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:

> On Thu, Jul 16, 2020 at 09:13:45PM +0530, Vishwa Kalyankar wrote:
> > 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
>
> It looks like they're returning different number of rows, so definitely
> not the
> same DB.
>
> Also, they're performing about the same now...
>
> It looks like you didn't set shared_buffers, even for a machine with 64GB
> RAM.
> I think it's unusual to keep the default.
>
> On Thu, Jul 16, 2020 at 10:21:35PM +0530, Vishwa Kalyankar wrote:
> > Both the db's configurations are not same, I have tuned the db in both
> > machines according to https://pgtune.leopard.in.ua/#/
>
> It looks like your low-end machine has no settings at all ?
> Did you forget to restart the server or use SET instead of ALTER SYSTEM
> SET ?
>
> > IPDS_KSEB=# set track_io_timing TO on;
> > IPDS_KSEB=# explain (analyze,buffers, settings) select * from
> kseb_geometry_trace_with_barrier_partition(5,'kottarakara_version',437,'htline',2);
> >
> > Function Scan on kseb_geometry_trace_with_barrier_partition
> > (cost=0.25..10.25 rows=1000 width=169) (actual
> time=24708.020..24708.048 rows=254 loops=1)
> > Buffers: shared hit=254235 read=1484
> > I/O Timings: read=827.509
> > Settings: effective_cache_size = '30GB', effective_io_concurrency =
> '2', max_parallel_workers = '24', max_parallel_workers_per_gather = '4',
> search_path = '"$user", public, topology', work_mem = '10MB'
> > Planning Time: 0.064 ms
> > Execution Time: 24772.587 ms
> >
> > Low End Machine
> > IPDS_KSEB=# explain (analyze,buffers, settings) select * from
> kseb_geometry_trace_with_barrier_partition(5,'kottarakara_version',437,'htline',2)
> ;
> > Function Scan on kseb_geometry_trace_with_barrier_partition
> (cost=0.25..10.25 rows=1000 width=169) (actual time=21870.311..21870.344
> rows=389 loops=1)
> > Buffers: shared hit=774945
> > Settings: search_path = '"$user", public, topology'
> > Planning Time: 0.089 ms
> > Execution Time: 21870.406 ms
>