Re: [HACKERS] Transactions involving multiple postgres foreign servers

On Tue, Jan 9, 2018 at 11:38 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Dec 27, 2017 at 9:40 PM, Tsunakawa, Takayuki
> <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
>> (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.
>
> If I understand correctly, XactLastRecEnd can be set by, for example,
> a HOT cleanup record, so that doesn't seem like a good thing to use.

Yes, that's right.

> Whether we need to use 2PC across remote nodes seems like it shouldn't
> depend on whether a local SELECT statement happened to do a HOT
> cleanup or not.

So I think we need to check if the top transaction is invalid or not as well.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center