> -----Original Message-----
> From: Mark Rotteveel [mailto:m...@lawinegevaar.nl]
> Sent: Miércoles, 07 de Mayo de 2014 8:14
>
> As the value of RDB$TRANSACTION_STATE is modified, I assume
> this code (or
> something very similar) is actually called, but then the `else` branch
> shown above. What does TRA_prepare2 mean here? Note that the specific
> scenario that triggered my question is a transaction recovery
> case, where
> the transaction is reconnected: transaction was prepared, but not
> committed/rolled back, then the connection was
> abandoned/destroyed; new
> connections recovers transaction and commits (or rolls back).
MET_prepare() writes a record in RDB$TRANSACTIONS and as Vlad said,
TRA_prepare() calls MET... only if you pass a text:
TRA_prepare:
// Functional desc: Put a transaction into limbo
....
if (msg && length)
{
MET_prepare(tdbb, transaction, length, msg);
transaction->tra_flags |= TRA_prepare2;
}
TRA_prepare2 is the indication that you are signaling all members of a
distributed transaction "pay attention, we are going to commit this
multi-connection mess".
In other words, when you prepare a 2PC txn, you have the sequence:
- jrd.cpp's JTransaction::prepare_tra() (prepare a txn for commit, first
phase of 2PC)
- jrd.cpp's prepare_tra()
- TRA_prepare()
- MET_prepare() -> writes to rdb$transactions and activates TRA_prepare2 but
it's called only if you passed a message to TRA_prepare().
Now, when you commit or rollback:
Only with the flags TRA_prepare2 or TRA_reconnected activated, TRA_commit
does
MET_update_transaction(tdbb, transaction, true);
and TRA_rollback does
MET_update_transaction(tdbb, transaction, false);
then we reach the code I showed in the previous letter:
void MET_update_transaction(thread_db* tdbb,
jrd_tra* transaction, const bool do_commit)
{
....
if (do_commit && (transaction->tra_flags & TRA_prepare2))
ERASE X
else
{
MODIFY X
X.RDB$TRANSACTION_STATE = do_commit ?
RDB$TRANSACTIONS.RDB$TRANSACTION_STATE.COMMITTED :
RDB$TRANSACTIONS.RDB$TRANSACTION_STATE.ROLLED_BACK;
END_MODIFY
}
Now it's evident what Vlad said: no message when preparing to commit implies
no TRA_prepare2 activated and in turn, it means the deletion won't happen.
There will be only an update.
The code is consistent. However if you're managing the 2PC trick in other
ways, we can allow the deletion (commenting the protection code is one
line), but how can we be sure you're deleting only what belongs to your
distributed transaction?
C.
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