On Mon, Feb 23, 2009 at 4:16 PM, Farhan Husain <russoue@xxxxxxxxx> wrote: > Hello, > > I am doing a performance comparison between running Jena with MySQL and > Postgres. I used the 8.3-community version of Postgres and MySQL 5.0.67. I > have run several queries to both MySQL and Postgres and all of them took > similar amount of time to execute except one. For the following query to a > table having 10,003,728 rows, MySQL takes 0.11 seconds to return results > whereas Postgres takes like 1 hour and 20 minutes! > > Query: > > 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; > > Table: > > Table "public.jena_g1t1_stmt" > Column | Type | Modifiers > ---------+-------------------- > ----+----------- > subj | character varying(250) | not null > prop | character varying(250) | not null > obj | character varying(250) | not null > graphid | integer | > Indexes: > "jena_g1t1_stmt_ixo" btree (obj) > "jena_g1t1_stmt_ixsp" btree (subj, prop) > > Machine: SunOS 5.10 Generic_127111-11 sun4u sparc SUNW, Sun-Fire-880 > Memory: 4 GB > Number of physical processors: 2 > > I tried to re-arrage the query but each time the amount of time needed is > the same. Can anyone help me find the answer to why Postgres is taking so > much time? > > I can provide any other information needed and also the data if anyone > wants. What is the locale of your database? I.e.: # show lc_collate ; lc_collate ------------- en_US.UTF-8 (1 row) If it's not C then string compares are going to probably need special indexes to work the way you expect them. (varchar pattern ops). Look here for more information: http://www.postgresql.org/docs/8.3/static/indexes-opclass.html -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
