From: | <david(dot)sahagian(at)emc(dot)com> |
---|---|
To: | <pgsql-general(at)postgresql(dot)org> |
Subject: | successive select statements |
Date: | 2011-11-21 22:56:42 |
Message-ID: | F3CBFBA88397EA498B22A05FFA9EC49D59FFEAA7@MX22A.corp.emc.com |
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Lists: | pgsql-general |
In postgresql.org/docs/9.1/static/transaction-iso.html I read
13.2.1. Read Committed Isolation Level
. . . two successive SELECT commands can see different data, even though they are within a single transaction . . .
Please consider this code being executed by postgres:
= = = = = = = = = =
select some_int from tableX
union all
select another_int from tableY
;
= = = = = = = = = =
Are these two select statements considered "successive" when isolation == Read Committed ?
Or are they instead guaranteed to see the same snapshot of the database ?
Also, please consider this code being executed by postgres:
= = = = = = = = = =
CREATE Or Replace FUNCTION fx_one() RETURNS setof integer AS
$$
select some_int from tableX;
$$ LANGUAGE 'sql';
CREATE Or Replace FUNCTION fx_two() RETURNS setof integer AS
$$
select another_int from tableY;
$$ LANGUAGE 'sql';
select * from fx_one()
union all
select * from fx_two()
;
= = = = = = = = = =
Are the two select statements inside fx_one and fx_two considered "successive" when isolation == Read Committed ?
Or are they instead guaranteed to see the same snapshot of the database ?
Thanks,
-dvs-
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