Re: constraint with reference to the same table - Mailing list pgsql-performance

Hi,

Can I confirm what this means then ..

For large table's each column with ref. inegritry I should create an index on those columns ?

So if I create a table like this :
CREATE TABLE business_businesstype
(
b_bt_id serial PRIMARY KEY,
b_id integer REFERENCES business ON UPDATE CASCADE ON DELETE CASCADE NOT NULL,
bt_id integer REFERENCES businesstype ON UPDATE CASCADE ON DELETE CASCADE NOT NULL
);

I should then create 2 index's

CREATE  INDEX business_idx ON  business_businesstype (business);
CREATE  INDEX businesstype_idx ON  business_businesstype (businesstype);

Thanks
Regards
Rudi.



Stephan Szabo wrote:

On Thu, 15 May 2003, Victor Yegorov wrote:
 

I'm using PostgreSQL 7.3.1 on i686-pc-linux-gnu, compiled by GCC egcs-2.91.66.

Here is topic. Table transactions:

=> \d transactions     Table "public.transactions"  Column    |     Type     | Modifiers
-------------+--------------+-----------trxn_id     | integer      | not nulltrxn_ret    | integer      |trxn_for    | integer      |status      | numeric(2,0) | not nullauth_status | numeric(2,0) | not null
Indexes: transactions_pkey primary key btree (trxn_id)
Foreign Key constraints: trxns_id FOREIGN KEY (trxn_id) REFERENCES connections(conn_id) ON UPDATE NO ACTION ON DELETE NO ACTION,                        trxns_ret FOREIGN KEY (trxn_ret) REFERENCES transactions(trxn_id) ON UPDATE NO ACTION ON DELETE NO ACTION,                        trxns_for FOREIGN KEY (trxn_for) REFERENCES transactions(trxn_id) ON UPDATE NO ACTION ON DELETE NO ACTION

As you can see, trxns_ret and trxns_for constraints references to the same table they come from.

Maintenance of system includes the following step:
delete from transactions where transactions.trxn_id = uneeded_trxns.trxn_id;
transactions volume is about 10K-20K rows.
uneeded_trxns volume is about 3K-5K rows.


Problem: It takes to MUCH time. EXPLAIN says:

I was waiting for about 30 minutes and then hit ^C.

After some time spent dropping indexes and constraints, I've found out, that problem was in
those 2 "cyclic" constraints. After drop, query passed in some seconds (that is suitable).

Question: why so?   

For each row dropped it's making sure that no row has either a trxn_ret or
trxn_for that pointed to that row.  If those columns aren't indexed it's
going to be amazingly slow (if they are indexed it'll probably only be
normally slow ;) ).



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