XACT_EVENT for 'commit prepared'
Hi hackers,
I found that in enum XactEvent, there is 'XACT_EVENT_PREPARE' for
'prepare transaction', but there is no event for 'commit prepared' or
'rollback prepared'.
For the following SQL:
------------------------------------------------
begin;
create table test(a int);
PREPARE TRANSACTION 'foo';
rollback prepared 'foo';
-------------------------------------------------
When executing ' rollback prepared 'foo'; ', I expected to get
'XACT_EVENT_ABORT', but actually,
the event type is 'XACT_EVENT_COMMIT'.
I think XACT_EVENT_COMMIT_PREPARED and XACT_EVENT_ROLLBACK_PREPARED can be
added in function 'FinishPreparedTransaction'
I'm confused why there are no related events for them.
Xiaoran Wang <fanfuxiaoran@gmail.com> writes:
I found that in enum XactEvent, there is 'XACT_EVENT_PREPARE' for
'prepare transaction', but there is no event for 'commit prepared' or
'rollback prepared'.
On the whole, it seems like a good idea to me that those commands
don't invoke event triggers. It is a core principle of 2PC that
if 'prepare' succeeded, 'commit prepared' must not fail. Invoking a
trigger during the second step would add failure cases and I'm not
sure what value it has.
regards, tom lane
Hi,
On 2024-06-07 11:19:40 -0400, Tom Lane wrote:
Xiaoran Wang <fanfuxiaoran@gmail.com> writes:
I found that in enum XactEvent, there is 'XACT_EVENT_PREPARE' for
'prepare transaction', but there is no event for 'commit prepared' or
'rollback prepared'.On the whole, it seems like a good idea to me that those commands
don't invoke event triggers. It is a core principle of 2PC that
if 'prepare' succeeded, 'commit prepared' must not fail. Invoking a
trigger during the second step would add failure cases and I'm not
sure what value it has.
Event triggers? Isn't this about RegisterXactCallback?
XACT_EVENT_COMMIT is called after the commit record has been flushed and the
procarray has been modified. Thus a failure in the hook has somewhat limited
consequences. I'd assume XACT_EVENT_COMMIT_PREPARED would do something
similar.
I suspect the reason we don't callback for 2pc commit/rollback prepared is
simpl: The code for doing a 2pc commit prepared lives in twophase.c, not
xact.c...
Greetings,
Andres Freund