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Re: Slow Query

From: Bob Lunney <bob_lunney(at)yahoo(dot)com>
To: pgsql-performance(at)postgresql(dot)org, PamOzer <pozer(at)automotive(dot)com>
Subject: Re: Slow Query
Date: 2010-08-27 00:19:37
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
We need more information than that, like:

What version of PostgreSQL?
What does the hardware look like?
What does the disk and tablespace layout look like?
How are your configuration variables set?

Other than that, are the statistics up to date on the VehicleMake table?

Bob Lunney

--- On Thu, 8/26/10, Ozer, Pam <pozer(at)automotive(dot)com> wrote:

From: Ozer, Pam <pozer(at)automotive(dot)com>
Subject: [PERFORM] Slow Query
To: pgsql-performance(at)postgresql(dot)org
Date: Thursday, August 26, 2010, 8:03 PM


I am new to Postgres and I am trying to understand the
Explain Analyze so I can tune the following query.  I run the same query using
mysql and it takes less than 50ms.  I run it on postgres and it takes 10
seconds. I feel like I am missing something very obvious. (VehicleUsed is a big
table over 750,000records) and datasetgroupyearmakemodel has 150000 records. 


It looks like the cost is highest in the Hash Join  on
Postalcode.   Am I reading this correctly.?  I do have indexes on the
lower(postalcode) in both tables.  Why wouldn’t be using the index?  Thanks
in advance for any help. 


Here is my query: 


select  distinct VehicleMake.VehicleMake 

from VehicleUsed 

inner join PostalCodeRegionCountyCity on ( lower (
VehicleUsed.PostalCode ) = lower ( PostalCodeRegionCountyCity.PostalCode ) ) 




 inner join VehicleMake on ( VehicleUsed.VehicleMakeId =
VehicleMake.VehicleMakeId ) 


( DatasetGroupYearMakeModel.DatasetGroupId = 3 )  and 

 ( VehicleUsed.DatasetId <> 113 )  

 and ( VehicleUsed.ProductGroupId <> 13 )  

 and ( PostalCodeRegionCountyCity.RegionId = 36 ) 

order by VehicleMake.VehicleMake 

 limit 500000 


Here is the explain analyze 


"Limit  (cost=38292.53..38293.19 rows=261 width=8)
(actual time=10675.857..10675.892 rows=42 loops=1)" 

"  ->  Sort  (cost=38292.53..38293.19 rows=261
width=8) (actual time=10675.855..10675.868 rows=42 loops=1)" 

"        Sort Key: vehiclemake.vehiclemake" 

"        Sort Method:  quicksort  Memory: 18kB" 

"        ->  HashAggregate  (cost=38279.45..38282.06
rows=261 width=8) (actual time=10675.710..10675.728 rows=42 loops=1)" 

"              ->  Hash Join  (cost=436.31..38270.51
rows=3576 width=8) (actual time=4.471..10658.291 rows=10425 loops=1)" 

"                    Hash Cond:
(vehicleused.vehiclemakeid = vehiclemake.vehiclemakeid)" 

"                    ->  Hash Join 
(cost=428.43..38213.47 rows=3576 width=4) (actual time=4.152..10639.742
rows=10425 loops=1)" 

"                          Hash Cond:
(lower((vehicleused.postalcode)::text) =

"                          ->  Nested Loop 
(cost=101.81..37776.78 rows=11887 width=10) (actual time=1.172..9876.586
rows=382528 loops=1)" 

"                                ->  Bitmap Heap
Scan on datasetgroupyearmakemodel  (cost=101.81..948.81 rows=5360 width=6)
(actual time=0.988..17.800 rows=5377 loops=1)" 

"                                      Recheck Cond:
(datasetgroupid = 3)" 

"                                      ->  Bitmap
Index Scan on datasetgroupyearmakemodel_i04  (cost=0.00..100.47 rows=5360
width=0) (actual time=0.830..0.830 rows=5377 loops=1)" 

"                                            Index
Cond: (datasetgroupid = 3)" 

"                                ->  Index Scan
using vehicleused_i10 on vehicleused  (cost=0.00..6.85 rows=1 width=12) (actual
time=0.049..1.775 rows=71 loops=5377)" 

"                                      Index Cond:
((vehicleused.vehiclemodelid = datasetgroupyearmakemodel.vehiclemodelid) AND
(vehicleused.vehiclemakeid = datasetgroupyearmakemodel.vehiclemakeid) AND
(vehicleused.vehicleyear = datasetgroupyearmakemodel.vehicleyear))" 

"                                      Filter:
((vehicleused.datasetid <> 113) AND (vehicleused.productgroupid <>

"                          ->  Hash 
(cost=308.93..308.93 rows=1416 width=6) (actual time=2.738..2.738 rows=1435

"                                ->  Bitmap Heap
Scan on postalcoderegioncountycity  (cost=27.23..308.93 rows=1416 width=6)
(actual time=0.222..0.955 rows=1435 loops=1)" 

"                                      Recheck Cond:
(regionid = 36)" 

"                                      ->  Bitmap
Index Scan on postalcoderegioncountycity_i05  (cost=0.00..26.87 rows=1416
width=0) (actual time=0.202..0.202 rows=1435 loops=1)" 

"                                            Index
Cond: (regionid = 36)" 

"                    ->  Hash  (cost=4.61..4.61
rows=261 width=10) (actual time=0.307..0.307 rows=261 loops=1)" 

"                          ->  Seq Scan on
vehiclemake  (cost=0.00..4.61 rows=261 width=10) (actual time=0.033..0.154
rows=261 loops=1)" 

"Total runtime: 10676.058 ms" 


Pam Ozer 

Data Architect 


  tel. 949.705.3468 

  Source Interlink Media 
  1733 Alton Pkwy Suite 100, Irvine, CA 92606

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