Re: [HACKERS] Transactions involving multiple postgres foreign servers - Mailing list pgsql-hackers

On Thu, Jan 19, 2017 at 4:04 PM, vinayak
<Pokale_Vinayak_q3@lab.ntt.co.jp> wrote:
>
> On 2017/01/16 17:35, Masahiko Sawada wrote:
>>
>> On Fri, Jan 13, 2017 at 3:48 PM, Masahiko Sawada <sawada.mshk@gmail.com>
>> wrote:
>>>
>>> On Fri, Jan 13, 2017 at 3:20 PM, Ashutosh Bapat
>>> <ashutosh.bapat@enterprisedb.com> wrote:
>>>>>
>>>>> Long time passed since original patch proposed by Ashutosh, so I
>>>>> explain again about current design and functionality of this feature.
>>>>> If you have any question, please feel free to ask.
>>>>
>>>> Thanks for the summary.
>>>>
>>>>> Parameters
>>>>> ==========
>>>>
>>>> [ snip ]
>>>>
>>>>> Cluster-wide atomic commit
>>>>> =======================
>>>>> Since the distributed transaction commit on foreign servers are
>>>>> executed independently, the transaction that modified data on the
>>>>> multiple foreign servers is not ensured that transaction did either
>>>>> all of them commit or all of them rollback. The patch adds the
>>>>> functionality that guarantees distributed transaction did either
>>>>> commit or rollback on all foreign servers. IOW the goal of this patch
>>>>> is achieving the cluster-wide atomic commit across foreign server that
>>>>> is capable two phase commit protocol.
>>>>
>>>> In [1], I proposed that we solve the problem of supporting PREPARED
>>>> transactions involving foreign servers and in subsequent mail Vinayak
>>>> agreed to that. But this goal has wider scope than that proposal. I am
>>>> fine widening the scope, but then it would again lead to the same
>>>> discussion we had about the big picture. May be you want to share
>>>> design (or point out the parts of this design that will help) for
>>>> solving smaller problem and tone down the patch for the same.
>>>>
>>> Sorry for confuse you. I'm still focusing on solving only that
>>> problem. What I was trying to say is that I think that supporting
>>> PREPARED transaction involving foreign server is the means, not the
>>> end. So once we supports PREPARED transaction involving foreign
>>> servers we can achieve cluster-wide atomic commit in a sense.
>>>
>> Attached updated patches. I fixed some bugs and add 003 patch that
>> adds TAP test for foreign transaction.
>> 003 patch depends 000 and 001 patch.
>>
>> Please give me feedback.
>
>
> I have tested prepared transactions with foreign servers but after preparing
> the transaction
> the following error occur infinitely.
> Test:
> =====
> =#BEGIN;
> =#INSERT INTO ft1_lt VALUES (10);
> =#INSERT INTO ft2_lt VALUES (20);
> =#PREPARE TRANSACTION 'prep_xact_with_fdw';
>
> 2017-01-18 15:09:48.378 JST [4312] ERROR:  function pg_fdw_resolve() does
> not exist at character 8
> 2017-01-18 15:09:48.378 JST [4312] HINT:  No function matches the given name
> and argument types. You might need to add explicit type casts.
> 2017-01-18 15:09:48.378 JST [4312] QUERY:  SELECT pg_fdw_resolve()
> 2017-01-18 15:09:48.378 JST [29224] LOG:  worker process: foreign
> transaction resolver (dbid 13119) (PID 4312) exited with exit code 1
> .....
>
> If we check the status on another session then it showing the status as
> prepared.
> =# select * from pg_fdw_xacts;
>  dbid  | transaction | serverid | userid |  status  | identifier
> -------+-------------+----------+--------+----------+------------------------
>  13119 |        1688 |    16388 |     10 | prepared | px_2102366504_16388_10
>  13119 |        1688 |    16389 |     10 | prepared | px_749056984_16389_10
> (2 rows)
>
> I think this is a bug.
>

Thank you for reviewing!

I think this is a bug of pg_fdw_resolver contrib module. I had
forgotten to change the SQL executed by pg_fdw_resolver process.
Attached latest version 002 patch.

Regards,

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

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