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Delete performance

From: Jana <jana(dot)vasseru(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Delete performance
Date: 2009-06-14 13:36:34
Message-ID: op.uvin28aig6o41l@truhlik (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
i have a table with about 250m records from which i want to delete thoose  
not contained in other table. I used this SQL query:
DELETE FROM data_structures_items WHERE id_data_structure NOT IN (
SELECT id_structure FROM data_structures);

This ran for 24hours and in the mean time it read more than 20TB of disk  
(then i run out of patience). Since the actual table is only about 16GB in  
size (the whole database is ~50GB) the only explanation i can think of is  
that the result of the sub-query is not cached and is  read again for each  
of 2.43655e+008 rows of data_structures_items table. Also i don't quite  
get why is data_individual_structures_pkey having ~52MB when the actual  
data contained is only ~343kb. Autovacuum is on and before doing this  
query i also ran vacum full analyze. Please tell me there is some logic in  
this and i am doing something wrong.

SELECT relname, reltuples, relpages FROM pg_class ;
relname	reltuples	relpages
data_structures	85820	2002
data_structures_id_individual_state	85820	6526
data_structures_id_structure_seq	1	1
data_structures_items	2.43655e+008	2030460
data_structures_items_depth	2.43655e+008	675971
data_structures_items_id_data_structure	2.43655e+008	668184
data_structures_items_id_data_structure_item_seq	1	1
data_structures_items_left	2.43655e+008	676334
data_structures_items_pkey	2.43655e+008	668074
data_individual_structures_pkey 85820	6526

CREATE TABLE data_structures_items
   id_data_structure_item serial NOT NULL,
   id_data_structure integer NOT NULL,
   "text" character varying(255) NOT NULL,
   lft integer NOT NULL,
   rght integer NOT NULL,
   depth integer NOT NULL,
   description character varying(255),
   CONSTRAINT data_structures_items_pkey PRIMARY KEY  

CREATE INDEX data_structures_items_depth
   ON data_structures_items
   USING btree

CREATE INDEX data_structures_items_id_data_structure
   ON data_structures_items
   USING btree

CREATE INDEX data_structures_items_left
   ON data_structures_items
   USING btree

CREATE TABLE data_structures
   id_structure serial NOT NULL,
   id_individual_state integer NOT NULL,
   "text" text,
   "timestamp" timestamp(0) without time zone DEFAULT now(),
   CONSTRAINT data_individual_structures_pkey PRIMARY KEY (id_structure),
   CONSTRAINT data_structures_fk FOREIGN KEY (id_individual_state)
       REFERENCES data_individual_states (id_individual_state) MATCH SIMPLE
ALTER TABLE data_structures OWNER TO sanae;

CREATE INDEX data_structures_id_individual_state
   ON data_structures
   USING btree


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Subject: Re: Delete performance
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