Re: Foreign join pushdown vs EvalPlanQual

On Thu, Nov 26, 2015 at 12:04 AM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> The attached patch adds: Path *fdw_outerpath field to ForeignPath node.
> FDW driver can set arbitrary but one path-node here.
> After that, this path-node shall be transformed to plan-node by
> createplan.c, then passed to FDW driver using GetForeignPlan callback.
> We expect FDW driver set this plan-node on lefttree (a.k.a outerPlan).
> The Plan->outerPlan is a common field, so patch size become relatively
> small. FDW driver can initialize this plan at BeginForeignScan, then
> execute this sub-plan-tree on demand.
>
> Remaining portions are as previous version. ExecScanFetch is revised
> to call recheckMtd always when scanrelid==0, then FDW driver can get
> control using RecheckForeignScan callback.
> It allows FDW driver to handle (1) EPQ recheck on underlying scan nodes,
> (2) reconstruction of joined tuple, and (3) EPQ recheck on join clauses,
> by its preferable implementation - including execution of an alternative
> sub-plan.
>
>> There seems to be no changes to make_foreignscan.  Is that OK?
>>
> create_foreignscan_path(), not only make_foreignscan().
>
> This patch is not tested by actual FDW extensions, so it is helpful
> to enhance postgres_fdw to run the alternative sub-plan on EPQ recheck.

I have done some editing and some small revisions on this patch.
Here's what I came up with.  The revisions are mostly cosmetic, but I
revised it a bit so that the signature of GetForeignPlan need not
change.  Also, I made nodeForeignScan.c do some of the outer plan
handling automatically, and I fixed the compile breaks in
contrib/file_fdw and contrib/postgres_fdw.

Comments/review/testing are very welcome.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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