Re: Effective usage without unique key -- suggestion

On Wednesday 07 Aug 2002 9:27 am, Bhuvan A wrote:
> Hi,
>
> I am using postgresql 7.2.1 on redhat linux 7.3
>
> I have a table in very high production database which is circulating
> several thousands of records per day ie.. count does not exceed several
> thousands.  Here for some technical reason i dont have unique key on this
> table, but it should contain unique records. I know that without using
> unique index it can be achieved in any of the following methods.

Why don't you create a unique index on the fields concerned? You can always
create a functional index if uniqueness is a complicated thing for you.

CREATE TABLE foo (a int, b int);

CREATE FUNCTION foo_add(int, int) RETURNS int AS ' SELECT $1 + $2;
' LANGUAGE 'sql' WITH (iscachable);

CREATE UNIQUE INDEX foo_uniq_idx ON foo ( foo_add(a,b) );

richardh=> INSERT INTO foo values (1,4);
INSERT 7024674 1
richardh=> INSERT INTO foo values (2,4);
INSERT 7024675 1
richardh=> INSERT INTO foo values (2,3);
ERROR:  Cannot insert a duplicate key into unique index foo_uniq_idx

> Method 1
>   * check for the record.
>   * if exists update, else insert
>
> Method 2
>   * delete the record (trigger on before insert)
>   * insert the record
>
> So Can you please suggest the best among the above 2 methods?
>
> BTW, internals of the above 2 methods would be different. For example in
> method 2, frequent deletion of records calls for vacuuming the database.
> FYI, i does VACUUM ANALYZE every day. So Can you please suggest the best
> among the above 2 methods which well suits me and to use postgres more
> effectively?

Don't think it matters which way you do it with MVCC - updating is equivalent
to a delete + insert. You say this table has a high rate of change, so you
might want to VACUUM it more often than daily.

- Richard Huxton