Re: Same query - Slow in production

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I added to the exists query qualifier: AND cp.category_id = 1000962 (in addition to the cp.category_id = ac.category_id)

Now I am getting a much better query plan on our production server:

Index Scan using attribute_category__category_id_fk_idx on attribute_category ac (cost=0.00..485.71 rows=7 width=4) (actual time=0.104..0.351 rows=5 loops=1)
   Index Cond: (category_id = 1000962)
   Filter: (((is_browsable)::text = 'true'::text) AND (subplan))
   SubPlan
-> Nested Loop (cost=0.00..24.77 rows=1 width=0) (actual time=0.058..0.058 rows=1 loops=5) -> Index Scan using x_category_product__category_id_fk_idx on category_product cp (cost=0.00..6.01 rows=1 width=4) (actual time=0.014..0.014 rows=1 loops=5) Index Cond: ((category_id = $1) AND (category_id = 1000962)) Filter: (((product_is_active)::text = 'true'::text) AND ((product_status_code)::text = 'complete'::text)) -> Index Scan using product_attribute_value__product_id_fk_idx on product_attribute_value pav (cost=0.00..18.75 rows=1 width=4) (actual time=0.041..0.041 rows=1 loops=5)
                 Index Cond: (pav.product_id = "outer".product_id)
Filter: ((attribute_id = $0) AND (status_code IS NULL))
Total runtime: 0.558 ms
(12 rows)

It is using the x_category_product__category_id_fk_idx on category_product instead of the category_product__category_id_is_active_and_status_idx index as on our backup server. Still not sure what's causing the differences in query execution between the servers, but at least the query is fast again.

Brian

On 10-May-06, at 4:39 PM, Brian Wipf wrote:

I'm trying to determine why an identical query is running approximately 500 to 1000 times slower on our production database compared to our backup database server.

Both database servers are dual 2.3 GHz G5 Xserves running PostgreSQL 8.1.3; both are configured with 8GB of RAM with identical shared memory settings; both postgresql.conf files are identical; both databases have identical indexes defined.

The three relevant tables are all clustered the same, although I'm not sure when clustering was last performed on either server. All three tables have recently been analyzed on both servers.

The different explain plans for this query seem to be consistent on both servers regardless of category and the production server is consistently and drastically slower than the backup server.

If anyone has any ideas on how to have the production server generate the same explain plan as the backup server, or can suggest anything I might want to try, I would greatly appreciate it.

Brian Wipf
ClickSpace Interactive Inc.
<brian@xxxxxxxxxxxxxx>

Here's the query:

SELECT	ac.attribute_id
FROM	attribute_category ac
WHERE	is_browsable = 'true' AND
	category_id = 1000962 AND
	EXISTS 	(	SELECT 	'X'
			FROM 	product_attribute_value pav,
				category_product cp
			WHERE 	pav.attribute_id = ac.attribute_id AND
				pav.status_code is null AND
				pav.product_id = cp.product_id AND
				cp.category_id = ac.category_id AND
				cp.product_is_active = 'true' AND
				cp.product_status_code = 'complete'
	)

Explain plans:

Fast (backup server):
Index Scan using attribute_category__category_id_fk_idx on attribute_category ac (cost=0.00..47943.34 rows=7 width=4) (actual time=0.110..0.263 rows=5 loops=1)
   Index Cond: (category_id = 1000962)
   Filter: (((is_browsable)::text = 'true'::text) AND (subplan))
   SubPlan
-> Nested Loop (cost=0.00..7983.94 rows=3 width=0) (actual time=0.043..0.043 rows=1 loops=5) -> Index Scan using category_product__category_id_is_active_and_status_idx on category_product cp (cost=0.00..4362.64 rows=1103 width=4) (actual time=0.013..0.015 rows=2 loops=5) Index Cond: ((category_id = $1) AND ((product_is_active)::text = 'true'::text) AND ((product_status_code)::text = 'complete'::text)) -> Index Scan using product_attribute_value__product_id_fk_idx on product_attribute_value pav (cost=0.00..3.27 rows=1 width=4) (actual time=0.016..0.016 rows=1 loops=8)
                 Index Cond: (pav.product_id = "outer".product_id)
Filter: ((attribute_id = $0) AND (status_code IS NULL))
Total runtime: 0.449 ms
(11 rows)

Slow (production server):
Index Scan using attribute_category__category_id_fk_idx on attribute_category ac (cost=0.00..107115.90 rows=7 width=4) (actual time=1.472..464.437 rows=5 loops=1)
   Index Cond: (category_id = 1000962)
   Filter: (((is_browsable)::text = 'true'::text) AND (subplan))
   SubPlan
-> Nested Loop (cost=18.33..23739.70 rows=4 width=0) (actual time=92.870..92.870 rows=1 loops=5) -> Bitmap Heap Scan on product_attribute_value pav (cost=18.33..8764.71 rows=2549 width=4) (actual time=10.191..45.672 rows=5869 loops=5)
                 Recheck Cond: (attribute_id = $0)
                 Filter: (status_code IS NULL)
-> Bitmap Index Scan on product_attribute_value__attribute_id_fk_idx (cost=0.00..18.33 rows=2952 width=0) (actual time=9.160..9.160 rows=33330 loops=5)
                       Index Cond: (attribute_id = $0)
-> Index Scan using x_category_product_pk on category_product cp (cost=0.00..5.86 rows=1 width=4) (actual time=0.007..0.007 rows=0 loops=29345) Index Cond: ((cp.category_id = $1) AND ("outer".product_id = cp.product_id)) Filter: (((product_is_active)::text = 'true'::text) AND ((product_status_code)::text = 'complete'::text))
Total runtime: 464.667 ms
(14 rows)

Table Descriptions:

\d attribute_category;
         Table "public.attribute_category"
     Column      |         Type         | Modifiers
-----------------+----------------------+-----------
attribute_id    | integer              | not null
category_id     | integer              | not null
is_browsable    | character varying(5) |
is_required     | character varying(5) |
sort_order      | integer              |
default_unit_id | integer              |
Indexes:
"attribute_category_pk" PRIMARY KEY, btree (attribute_id, category_id)
    "attribute_category__attribute_id_fk_idx" btree (attribute_id)
"attribute_category__category_id_fk_idx" btree (category_id) CLUSTER
Foreign-key constraints:
"attribute_category_attribute_fk" FOREIGN KEY (attribute_id) REFERENCES attribute(attribute_id) DEFERRABLE INITIALLY DEFERRED "attribute_category_category_fk" FOREIGN KEY (category_id) REFERENCES category(category_id) DEFERRABLE INITIALLY DEFERRED

\d product_attribute_value;
             Table "public.product_attribute_value"
           Column           |         Type          | Modifiers
----------------------------+-----------------------+-----------
attribute_id               | integer               | not null
attribute_unit_id          | integer               |
attribute_value_id         | integer               |
boolean_value              | character varying(5)  |
decimal_value              | numeric(30,10)        |
product_attribute_value_id | integer               | not null
product_id                 | integer               | not null
product_reference_id       | integer               |
status_code                | character varying(32) |
Indexes:
"product_attribute_value_pk" PRIMARY KEY, btree (product_attribute_value_id) "product_attribute_value__attribute_id_fk_idx" btree (attribute_id) "product_attribute_value__attribute_unit_id_fk_idx" btree (attribute_unit_id) "product_attribute_value__attribute_value_id_fk_idx" btree (attribute_value_id)
    "product_attribute_value__decimal_value_idx" btree (decimal_value)
"product_attribute_value__product_id_fk_idx" btree (product_id) CLUSTER "product_attribute_value__product_reference_id_fk_idx" btree (product_reference_id)
Foreign-key constraints:
"product_attribute_value_attribute_fk" FOREIGN KEY (attribute_id) REFERENCES attribute(attribute_id) DEFERRABLE INITIALLY DEFERRED "product_attribute_value_attributeunit_fk" FOREIGN KEY (attribute_unit_id) REFERENCES attribute_unit(attribute_unit_id) DEFERRABLE INITIALLY DEFERRED "product_attribute_value_attributevalue_fk" FOREIGN KEY (attribute_value_id) REFERENCES attribute_value(attribute_value_id) DEFERRABLE INITIALLY DEFERRED "product_attribute_value_product_fk" FOREIGN KEY (product_id) REFERENCES product(product_id) DEFERRABLE INITIALLY DEFERRED "product_attribute_value_productreference_fk" FOREIGN KEY (product_reference_id) REFERENCES product(product_id) DEFERRABLE INITIALLY DEFERRED

\d category_product;
             Table "public.category_product"
       Column        |          Type          | Modifiers
---------------------+------------------------+-----------
category_id         | integer                | not null
product_id          | integer                | not null
en_name_sort_order  | integer                |
fr_name_sort_order  | integer                |
merchant_sort_order | integer                |
price_sort_order    | integer                |
merchant_count      | integer                |
is_active           | character varying(5)   |
product_is_active   | character varying(5)   |
product_status_code | character varying(32)  |
product_name_en     | character varying(512) |
product_name_fr     | character varying(512) |
product_click_count | integer                |
Indexes:
"x_category_product_pk" PRIMARY KEY, btree (category_id, product_id) "category_product__category_id_is_active_and_status_idx" btree (category_id, product_is_active, product_status_code)
    "category_product__is_active_idx" btree (is_active)
"category_product__merchant_sort_order_idx" btree (merchant_sort_order) "x_category_product__category_id_fk_idx" btree (category_id) CLUSTER
    "x_category_product__product_id_fk_idx" btree (product_id)
Foreign-key constraints:
"x_category_product_category_fk" FOREIGN KEY (category_id) REFERENCES category(category_id) DEFERRABLE INITIALLY DEFERRED "x_category_product_product_fk" FOREIGN KEY (product_id) REFERENCES product(product_id) DEFERRABLE INITIALLY DEFERRED




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