The documentation states that "concurrent execution of a set of
Serializable transactions is guaranteed to produce the same effect as
running them one at a time in some order."
I'm not sure how the following behavior fits that definition. (Note that
this is just an experiment, not a use case. Purely academic.) I run these
transactions sequentially, and I get a different result than if I run them
concurrently.
This is in 9.3.0
First, I set up a table.
create table x (value int);
Then I run the following transactions. If I run them sequentially, in
either order, I get one row in table x. If I run them concurrently, I get
no rows in x.
It seems like one of these should error out and not commit, so I must be
missing some stipulation.
Feel free to repeat this result.
=========
begin;
set transaction isolation level serializable;
create table z ();
select pg_sleep(5);
insert into x (value)
select 0
where exists (select relname from pg_class
where relname = 'y')
and exists (select relname from pg_class
where relname = 'z');
commit;
=========
begin;
set transaction isolation level serializable;
create table y ();
select pg_sleep(5);
insert into x (value)
select 0
where exists (select relname from pg_class
where relname = 'y')
and exists (select relname from pg_class
where relname = 'z');
commit;
