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.


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