Re: Autonomous Transaction is back

On Sat, Aug 22, 2015 at 2:23 AM, Noah Misch  wrote:
>> > Can you get away with only looking at tuples though?  For example,
>> > what about advisory locks?  Table locks?
>>
>> Well, that's an interesting question.  Can we get away with regarding
>> those things as non-conflicting, as between the parent and child
>> transactions?
>
> For system lock types, no.  While one could define advisory locks to work
> differently, we should assume that today's advisory lockers have expectations
> like those of system lockers.  An autonomous transaction should not bypass any
> lock that a transaction of another backend could not bypass.

Why?

Suppose you do this:

BEGIN;
DECLARE CURSOR foo FOR SELECT * FROM foo;
BEGIN AUTONOMOUS TRANSACTION;
ALTER TABLE foo ALTER bar TYPE int;

This has got to fail for safety reasons, but CheckTableNotInUse() is
on it.  Suppose you do this:

BEGIN;
LOCK foo;
BEGIN AUTONOMOUS TRANSACTION;
INSERT INTO foo VALUES ('spelunk');

How will making this fail improve anything?

-- 
Robert Haas
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