Re: xmin increasing within a transaction block?

Luca Ferrari wrote:
> Hi all,
> I suspect this has a trivial explaination, but this is what I'm experiencing:
>
> > CREATE TABLE foo( i int );
> > BEGIN;
> * > INSERT INTO foo(i) VALUES( 1 );
> * > INSERT INTO foo(i) VALUES( 2 );
> * > SELECT xmin, cmin, xmax, cmax, i FROM foo;
> xmin | cmin | xmax | cmax | i
> ------+------+------+------+---
> 2466 | 0 | 0 | 0 | 1
> 2467 | 1 | 0 | 1 | 2
> (2 rows)

With this example both rows show the same xmin to me, which is what I'd
expect.

> Why is xmin greater than the current transaction id (and most notably
> not "fixed")?

Something is using subtransactions there. My first guess would be that
there are triggers with EXCEPTION blocks, but your example doesn't show
any. Or maybe you have event triggers.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services