Re: ERROR: subtransaction logged without previous top-level txn record

Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:

>> I don't believe you can that without persisting additional
>> data. Basically, what we need is list of transactions who are running at
>> the point of snapshot serialization *and* already wrote something before
>> it -- those we hadn't seen in full and can't decode. We have no such
>> data currently. The closest thing we have is xl_running_xacts->nextXid,
>> but
>>
>> 1) issued xid doesn't necessarily means xact actually wrote something,
>> so we can't just skip xl_xact_assignment for xid < nextXid, it might
>> still be decoded
>> 2) snapshot might be serialized not at xl_running_xacts anyway
>>
>> Surely this thing doesn't deserve changing persisted data format.
>>
>
> I agree that it won't be a good idea to change the persisted data
> format, especially in back-branches. I don't see any fix which can
> avoid this without doing major changes in the code. Apart from this,
> we have to come up with a solution for point (3) discussed in the
> above email [1] which again could be change in design. I think we can
> first try to proceed with the patch
> 0002-Stop-demanding-that-top-xact-must-be-seen-before--v2 and then we
> can discuss the other patch. I can't see a way to write a test case
> for this, can you think of any way?

Yeah, let's finally get it.

Attached is raw version of isolation test triggering false
'subtransaction logged without...' (case (1)). However, frankly I don't
see much value in it, so I'm dubious whether it should be included in
the patch.