Обсуждение: intercepting where clause on a view or other performance tweak
Hi,
I have a table which contains generated static data (defined below) where the search_key field contains varying length strings.
There are 122,000 rows in the table
When the data is created the search_key field is ordered alphanumerically and assigned a unique order_key value starting at 1.
The table is defined as:
CREATE TABLE stuff
(
code integer NOT NULL DEFAULT 0,
search_key character varying(255),
order_key integer,
CONSTRAINT "PK_code" PRIMARY KEY (code)
)
CREATE INDEX order_key
ON stuff
USING btree
(order_key);
ALTER TABLE stuff CLUSTER ON order_key;
And a view defined as:
CREATE OR REPLACE VIEW stuff_view AS
select * from stuff
Running the following query takes 56+ ms as it does a seq scan of the whole table:
SELECT CODE FROM stuff
WHERE SEARCH_KEY LIKE 'AAAAAA%'
Running the following query takes 16+ ms as it does 2 index scans of the order_key index:
SELECT CODE FROM stuff
WHERE SEARCH_KEY LIKE 'AAAAAA%'
and order_key >=
(
SELECT order_key FROM stuff
WHERE SEARCH_KEY LIKE 'AA%'
order by order_key
limit 1
)
and order_key <
(
SELECT order_key FROM stuff
WHERE SEARCH_KEY LIKE 'AB%'
order by order_key
limit 1
)
Running the following query takes less than a second doing a single index scan:
SELECT CODE FROM stuff
WHERE SEARCH_KEY LIKE 'AAAAAA%'
and order_key >= 14417
and order_key < 15471
The problem query is always going to be in the first format.
It was my intention to either change the view to intercept the query using a rule and either
add the extra parameters from the second query
OR
Add a second table which contains the order_key ranges and
add the extra parameters from the third query
Is there an easier way to do this?
As always, thanks for you help…
Regards,
Russell Keane
INPS
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