On Fri, Jul 15, 2016 at 4:17 PM Kaixi Luo <kaixiluo@xxxxxxxxx> wrote:
Hello,I have a primary PostgreSQL server with 64GB of RAM that is replicated using streaming replication to a hot standby server with 16GB of RAM.
Do you have different hardware configuration for master and standby? I am not sure if that is the right thing to do. I usually prefer them to be equally sized and have same configuration. But may be someone else with more experience can comment better on that aspect.
My problem is as follows: I've detected a query that takes a long time to run on my primary server but runs very fast on the standby server. I did an EXPLAIN ANALYZE on the query:
What is the version of PostgreSQL on both servers? Check with
select version();
EXPLAIN ANALYZESELECT this_.id AS id1_31_0_,this_.nom AS nom2_31_0_,this_.nom_slug AS nom3_31_0_,this_.descripcio AS descripc4_31_0_,this_.url AS url5_31_0_,this_.data_captura AS data6_31_0_,this_.data_publicacio AS data7_31_0_,this_.propietari AS propieta8_31_0_,this_.privacitat AS privacit9_31_0_,this_.desnivellpujada AS desnive10_31_0_,this_.desnivellbaixada AS desnive11_31_0_,this_.longitud AS longitu13_31_0_,this_.beginpoint AS beginpo14_31_0_,this_.endpoint AS endpoin15_31_0_,this_.caixa3d AS caixa16_31_0_,this_.pic_id AS pic17_31_0_,this_.skill AS skill18_31_0_,this_.spatial_type AS spatial19_31_0_,this_.tags_cached AS tags20_31_0_,this_.images_cached AS images21_31_0_,this_.ncomments AS ncommen22_31_0_,this_.group_order AS group23_31_0_,this_.author AS author24_31_0_,this_.proper_a AS proper25_31_0_,this_.duration AS duratio26_31_0_,this_.isloop AS isloop27_31_0_,this_.seo_country AS seo28_31_0_,this_.seo_region AS seo29_31_0_,this_.seo_place AS seo30_31_0_,this_.source AS source31_31_0_,this_.source_name AS source32_31_0_,this_.api_key AS api33_31_0_,this_.ratingui AS ratingu34_31_0_,this_.nratings AS nrating35_31_0_,this_.trailrank AS trailra36_31_0_,this_.ncoords AS ncoords37_31_0_,this_.egeom AS egeom38_31_0_,this_.elevels AS elevels39_31_0_,this_.elevations AS elevati40_31_0_,this_.nphotoswpts AS nphotos41_31_0_,this_.nfavourited AS nfavour42_31_0_,this_.ncompanions AS ncompan43_31_0_,this_.group_id AS group44_31_0_FROM spatial_artifact this_WHERE this_.group_id IS NULLAND this_.propietari=7649ORDER BY this_.id DESC LIMIT 20
--PRIMARY SERVER (EXPLAIN ANALYZE output)"Limit (cost=0.43..22734.71 rows=20 width=604) (actual time=1804.124..293469.085 rows=20 loops=1)"" -> Index Scan Backward using "PK_SPATIAL_ARTIFACT" on spatial_artifact this_ (cost=0.43..7776260.84 rows=6841 width=604) (actual time=1804.121..293469.056 rows=20 loops=1)"" Filter: ((group_id IS NULL) AND (propietari = 7649))"" Rows Removed by Filter: 2848286""Total runtime: 293469.135 ms"
--STANDBY SERVER (EXPLAIN ANALYZE output)"Limit (cost=23533.73..23533.78 rows=20 width=604) (actual time=2.566..2.569 rows=20 loops=1)"" -> Sort (cost=23533.73..23550.83 rows=6841 width=604) (actual time=2.566..2.567 rows=20 loops=1)"" Sort Key: id"" Sort Method: top-N heapsort Memory: 35kB"" -> Index Scan using idx_own_spas on spatial_artifact this_ (cost=0.43..23351.70 rows=6841 width=604) (actual time=0.037..2.119 rows=618 loops=1)"" Index Cond: (propietari = 7649)""Total runtime: 2.612 ms"I've run ANALYZE on my table and have reindexed the index idx_own_spas on my primary server, but it hasn't helped.Here is the postgresql config of my two servers:--PRIMARY SERVER (postgresql.conf)shared_buffers = 8GBwork_mem = 42MBmaintenance_work_mem = 2GBeffective_cache_size = 44GB
what are the values of random_page_cost and seq_page_cost?
Also what might help here is the number of rows and pages in the table -
select relpages,reltuples, relname from pg_class where relname in ('idx_own_spas ','spatial_artifact','PK_SPATIAL_ARTIFACT');
--STANDBY SERVER (postgresql.conf)shared_buffers = 800MBwork_mem = 20MBmaintenance_work_mem = 128MBeffective_cache_size = 1024MB
Could you shed some light into why this is happening? Thank you.Cheers,Kaixi
--
--
Best Regards
Sameer Kumar | DB Solution Architect
ASHNIK PTE. LTD.
101 Cecil Street, #11-11 Tong Eng Building, Singapore 069 533
T: +65 6438 3504 | M: +65 8110 0350 | www.ashnik.com
