Re: Abnormal performance difference between Postgres and MySQL

On Mon, Feb 23, 2009 at 5:27 PM, Gregory Stark <stark(at)enterprisedb(dot)com>wrote:

> Farhan Husain <russoue(at)gmail(dot)com> writes:
>
> > I can provide any other information needed and also the data if anyone
> > wants.
>
> What did the query plans look like in both databases?
>
> In Postgres you can get the query plan with
>
> EXPLAIN ANALYZE select ...
>
> You can leave out the ANALYZE if you can't wait until the query completes
> but
> it will have much less information to diagnosis any problems.
>
> --
> Gregory Stark
> EnterpriseDB http://www.enterprisedb.com
> Ask me about EnterpriseDB's Slony Replication support!
>

Here is the output:

ingentadb=# EXPLAIN ANALYZE select A0.Subj, A2.Obj From jena_g1t1_stmt A0,
jena_g1t1_stmt A1, jena_g1t1_stmt A2 Where A0.Prop='Uv::
http://prismstandard.org/namespaces/1.2/basic/isPartOf' AND A0.Obj='Uv::
http://www.utdallas.edu/~farhan.husain/IngentaConnect/issue1_1' AND
A0.GraphID=1 AND A0.Subj=A1.Subj AND A1.Prop='Uv::
http://www.w3.org/1999/02/22-rdf-syntax-ns#type' AND A1.Obj='Uv::
http://metastore.ingenta.com/ns/structure/Article' AND A1.GraphID=1 AND
A0.Subj=A2.Subj AND A2.Prop='Uv::
http://prismstandard.org/namespaces/1.2/basic/startingPage' AND
A2.GraphID=1;

QUERY
PLAN

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Merge Join (cost=652089.37..665004.47 rows=733195 width=134) (actual
time=5410683.129..5410690.033 rows=30 loops=1)
Merge Cond: ((a0.subj)::text = (a1.subj)::text)
-> Sort (cost=86716.91..86796.78 rows=31949 width=208) (actual
time=76.395..76.423 rows=30 loops=1)
Sort Key: a0.subj
Sort Method: quicksort Memory: 24kB
-> Nested Loop (cost=0.00..84326.57 rows=31949 width=208) (actual
time=4.146..65.409 rows=30 loops=1)
-> Index Scan using jena_g1t1_stmt_ixo on jena_g1t1_stmt a0
(cost=0.00..5428.34 rows=487 width=74) (actual time=1.980..2.142 rows=30
loops=1)
Index Cond: ((obj)::text = 'Uv::
http://www.utdallas.edu/~farhan.husain/IngentaConnect/issue1_1'::text)
Filter: (((prop)::text = 'Uv::
http://prismstandard.org/namespaces/1.2/basic/isPartOf'::text) AND (graphid
= 1))
-> Index Scan using jena_g1t1_stmt_ixsp on jena_g1t1_stmt
a2 (cost=0.00..161.37 rows=51 width=134) (actual time=2.101..2.104 rows=1
loops=30)
Index Cond: (((a2.subj)::text = (a0.subj)::text) AND
((a2.prop)::text = 'Uv::
http://prismstandard.org/namespaces/1.2/basic/startingPage'::text))
Filter: (a2.graphid = 1)
-> Sort (cost=565372.46..568084.16 rows=1084680 width=74) (actual
time=5410606.604..5410606.628 rows=31 loops=1)
Sort Key: a1.subj
Sort Method: quicksort Memory: 489474kB
-> Seq Scan on jena_g1t1_stmt a1 (cost=0.00..456639.59
rows=1084680 width=74) (actual time=0.043..44005.780 rows=3192000 loops=1)
Filter: ((graphid = 1) AND ((prop)::text = 'Uv::
http://www.w3.org/1999/02/22-rdf-syntax-ns#type'::text) AND ((obj)::text =
'Uv::http://metastore.ingenta.com/ns/structure/Article'::text))
Total runtime: 5410691.012 ms
(18 rows)

--
Mohammad Farhan Husain
Research Assistant
Department of Computer Science
Erik Jonsson School of Engineering and Computer Science
University of Texas at Dallas