Hi Esturo,
Le 05/11/2019 à 10:35, Etsuro Fujita a écrit :
> Hi Gilles,
>
> On Sat, Nov 2, 2019 at 1:29 AM Gilles Darold <[email protected]> wrote:
>> As per the following code, t1 is a remote table through postgres_fdw:
>> test=# BEGIN;
>> BEGIN
>> test=# SELECT * FROM t1;
>> ...
>>
>> test=# PREPARE TRANSACTION 'gxid1';
>> ERROR: cannot prepare a transaction that modified remote tables
>> I have attached a patch to the documentation that adds remote tables to the
>> list of objects where any operation prevent using a prepared transaction,
>> currently it is just notified "operations involving temporary tables or the
>> session's temporary namespace".
> I'm not sure that's a good idea because file_fdw works well for
> PREPARE TRANSACTION! How about adding a note about that to the
> section of Transaction Management in the postgres_fdw documentation
> like the attached?
You are right, read only FDW can be used. A second point in favor of
your remark is that this is the responsibility of the FDW implementation
to throw an error when used with a prepared transaction and I see that
this is not the case for all FDW.
I have attached a single patch that include Etsuro Fujita's patch on
postgres_fdw documentation and mine on postgres_fdw error message with
the precision that it comes from postgres_fdw. The modification about
prepared transaction in PostgreSQL documentation has been removed.
--
Gilles Darold
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 7cd69cc709..077eaf46ee 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -725,7 +725,7 @@ pgfdw_xact_callback(XactEvent event, void *arg)
*/
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("cannot prepare a transaction that modified remote tables")));
+ errmsg("cannot prepare a transaction that has operated on postgres_fdw foreign tables")));
break;
case XACT_EVENT_PARALLEL_COMMIT:
case XACT_EVENT_COMMIT:
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 634a7141ef..ed369cb54b 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -483,6 +483,12 @@
COMMITTED</literal> local transaction. A future
<productname>PostgreSQL</productname> release might modify these rules.
</para>
+
+ <para>
+ Note that it is currently not supported by
+ <filename>postgres_fdw</filename> to prepare the remote transaction for
+ two-phase commit.
+ </para>
</sect2>
<sect2>
