Re: Update does not move row across foreign partitions in v11

On 2019/03/06 12:47, David Rowley wrote:
> On Wed, 6 Mar 2019 at 16:29, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> That means that rows can be moved from a local partition to a foreign
>> partition if the FDW supports it.
>
> It seems a bit light on detail to me. If I was a user I'd want to know
> what exactly the FDW needed to support this. Does it need a special
> partition move function? Looking at ExecFindPartition(), this check
> seems to be done in CheckValidResultRel() and is basically:
>
> case RELKIND_FOREIGN_TABLE:
> /* Okay only if the FDW supports it */
> fdwroutine = resultRelInfo->ri_FdwRoutine;
> switch (operation)
> {
> case CMD_INSERT:
> if (fdwroutine->ExecForeignInsert == NULL)
> ereport(ERROR,
> (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> errmsg("cannot insert into foreign table \"%s\"",
> RelationGetRelationName(resultRel))));
>
> Alternatively, we could just remove the mention about "if the FDW
> supports it", since it's probably unlikely for an FDW not to support
> INSERT.

AFAIK, there's no special support in FDWs for "tuple moving" as such. The
"if the FDW supports it" refers to the FDW's ability to handle tuple
routing. Note that moving/re-routing involves calling
ExecPrepareTupleRouting followed by ExecInsert on the new tupls after the
old tuple is deleted. If an FDW doesn't support tuple routing, then a
tuple cannot be moved into it. That's what that text is talking about.

Maybe, we should reword it as "if the FDW supports tuple routing", so that
a reader doesn't go looking around for "tuple moving support" in FDWs.

Thanks,
Amit