Re: AW: AW: relation ### modified while in use

At 10:10 23/10/00 -0400, Tom Lane wrote:
>
>I consider that behavior *far* safer than allowing schema changes to
>be seen mid-transaction. Consider the following example:
>
> Session 1 Session 2
>
> begin;
>
> INSERT INTO foo ...;
>
> ALTER foo ADD constraint;
>
> INSERT INTO foo ...;
>
> end;
>
>Which, if any, of session 1's insertions will be subject to the
>constraint? What are the odds that the dba will like the result?
>

In this case, wouldn't the answer depend on the isolation level of session
1? For serializable TX, then constraint would not apply; 'read committed'
would mean the constraint was visible on the second insert and at the commit.

I would err on the side of insisting all metadata changes occur in
serializable transactions to make life a little easier.

----------------------------------------------------------------
Philip Warner | __---_____
Albatross Consulting Pty. Ltd. |----/ - \
(A.B.N. 75 008 659 498) | /(@) ______---_
Tel: (+61) 0500 83 82 81 | _________ \
Fax: (+61) 0500 83 82 82 | ___________ |
Http://www.rhyme.com.au | / \|
| --________--
PGP key available upon request, | /
and from pgp5.ai.mit.edu:11371 |/