RE: [HACKERS] Transactions involving multiple postgres foreign servers

From: Masahiko Sawada [mailto:sawada(dot)mshk(at)gmail(dot)com]
> I've updated documentation of patches, and fixed some bugs. I did some
> failure tests of this feature using a fault simulation tool[1] for
> PostgreSQL that I created.
>
> 0001 patch adds a mechanism to track of writes on local server. This is
> required to determine whether we should use 2pc at commit. 0002 patch is
> the main part. It adds a distributed transaction manager (currently only
> for atomic commit), APIs for 2pc and foreign transaction manager resolver
> process. 0003 patch makes postgres_fdw support atomic commit using 2pc.
>
> Please review patches.

I'd like to join the review and testing of this functionality. First, some comments after taking a quick look at 0001:

(1)
Why don't you use the existing global variable MyXactFlags instead of the new TransactionDidWrite? Or, how about using XactLastRecEnd != 0 to determine the transaction did any writes? When the transaction only modified temporary tables on the local database and some data on one remote database, I think 2pc is unnecessary.

(2)
If TransactionDidWrite is necessary, I don't think you need to provide setter functions, because other transaction state variables are accessed globally without getter/setters. And you didn't create getter function for TransactionDidWrite.

(3)
heap_multi_insert() doesn't modify TransactionDidWrite. Is it sufficient to just remember heap modifications? Are other modifications on the coordinator node covered such as TRUNCATEand and REINDEX?

Questions before looking at 0002 and 0003:

Q1: Does this functionality work when combined with XA 2pc transactions?

Q2: Does the atomic commit cascade across multiple remote databases? For example:
* The local transaction modifies data on remote database 1 via a foreign table.
* A trigger fires on the remote database 1, which modifies data on remote database 2 via a foreign table.
* The local transaction commits.

Regards
Takayuki Tsunakawa