Transaction isolation levels

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Hi,

I'm having some trouble with transaction isolation levels, and would
appreciate some input on this.

According to the documentation of PostgreSQL 8.0.3, section 12.2:

"Read Committed is the default isolation level in PostgreSQL. When a
transaction runs on this isolation level, a SELECT query sees only data
committed before the query began; it never sees either uncommitted data
or changes committed during query execution by concurrent transactions."

Therefore, in this isolation level, I should not see data committed by
another concurrent transaction.

Now I open two terminals with a 'pgsql' command, and do the following:

terminal 1:
    geertj=> \set AUTOCOMMIT off
    geertj=> set transaction isolation level read committed;
    SET
    geertj=> create table products (id integer not null, code char(20)
not null);
    CREATE TABLE
    geertj=> commit; begin;
    COMMIT
    BEGIN

terminal 2:
    geertj=> \set AUTOCOMMIT off
    geertj=> set transaction isolation level read committed;
    SET
    geertj=> select * from products;
     id | code
    ----+------
    (0 rows)

terminal 1:
    geertj=> insert into products values (10, 'pr10');
    INSERT 34071 1
    geertj=> commit;
    COMMIT

terminal 2:
    geertj=> select * from products;
     id |         code
    ----+----------------------
     10 | pr10


As you see, the row inserted in the transaction from terminal 1 appears
into terminal 2, but terminal 2 had a transaction open that did not commit.

The top of section 12.2 of the manual tells that nonrepeatable reads may
happen in the 'read committed' isolation level. I can understand the
above behaviour in terms of this.  However, the start of section 12.2.1
tells that in read committed mode, you get a snapshot of the database
when the transaction starts, and that snapshot will not inlude committed
changes from other transactions. Who is right here?

Regards,
Geert



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