Re: Display of multi-target-table Modify plan nodes in EXPLAIN

Ashutosh Bapat <ashutosh.bapat@enterprisedb.com> writes:
> On Mon, Mar 23, 2015 at 10:51 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hm?  We don't have scan nodes that read more than one table, so I'm
>> not following your point.

> But in the text output you gave
> Update on public.pt1  (cost=0.00..321.05 rows=3541 width=46)
>    Update on public.pt1
>    Foreign Update on public.ft1
>      Remote SQL: UPDATE public.ref1 SET c1 = $2 WHERE ctid = $1
>    Foreign Update on public.ft2
>      Remote SQL: UPDATE public.ref2 SET c1 = $2 WHERE ctid = $1
>    Update on public.child3
>    ->  Seq Scan on public.pt1  (cost=0.00..0.00 rows=1 width=46)
>          Output: (pt1.c1 + 1), pt1.c2, pt1.c3, pt1.ctid
>    ... etc ...

> For ft1 there is only Update Remote SQL. whereas for child3 you have
> specified the Seq Scan as well.

I think you're confused by my perhaps-overly-abbreviated example.
Here's the whole output for the example in HEAD:

# explain update pt1 set c1=c1+1;                            QUERY PLAN                              
---------------------------------------------------------------------Update on pt1  (cost=0.00..321.05 rows=3541
width=46) Update on pt1  Foreign Update on ft1  Foreign Update on ft2  Update on child3  ->  Seq Scan on pt1
(cost=0.00..0.00rows=1 width=46)  ->  Foreign Scan on ft1  (cost=100.00..148.03 rows=1170 width=46)  ->  Foreign Scan
onft2  (cost=100.00..148.03 rows=1170 width=46)  ->  Seq Scan on child3  (cost=0.00..25.00 rows=1200 width=46)
 
(9 rows)

# explain verbose update pt1 set c1=c1+1;                                QUERY PLAN                                 
----------------------------------------------------------------------------Update on public.pt1  (cost=0.00..321.05
rows=3541width=46)  Update on public.pt1  Foreign Update on public.ft1    Remote SQL: UPDATE public.ref1 SET c1 = $2
WHEREctid = $1  Foreign Update on public.ft2    Remote SQL: UPDATE public.ref2 SET c1 = $2 WHERE ctid = $1  Update on
public.child3 ->  Seq Scan on public.pt1  (cost=0.00..0.00 rows=1 width=46)        Output: (pt1.c1 + 1), pt1.c2,
pt1.c3,pt1.ctid  ->  Foreign Scan on public.ft1  (cost=100.00..148.03 rows=1170 width=46)        Output: (ft1.c1 + 1),
ft1.c2,ft1.c3, ft1.ctid        Remote SQL: SELECT c1, c2, c3, ctid FROM public.ref1 FOR UPDATE  ->  Foreign Scan on
public.ft2 (cost=100.00..148.03 rows=1170 width=46)        Output: (ft2.c1 + 1), ft2.c2, ft2.c3, ft2.ctid        Remote
SQL:SELECT c1, c2, c3, ctid FROM public.ref2 FOR UPDATE  ->  Seq Scan on public.child3  (cost=0.00..25.00 rows=1200
width=46)       Output: (child3.c1 + 1), child3.c2, child3.c3, child3.ctid
 
(17 rows)

        regards, tom lane