At Mon, 9 Apr 2018 16:07:33 +0530, Ashutosh Bapat <ashutosh.ba...@enterprisedb.com> wrote in <cafjfprccjqsdt70eqkuockfinh3vowqzdzbg6yrozw_m0pw...@mail.gmail.com> > On Mon, Apr 9, 2018 at 3:53 PM, Ashutosh Bapat > <ashutosh.ba...@enterprisedb.com> wrote: > > On Mon, Apr 9, 2018 at 3:49 PM, Kyotaro HORIGUCHI > > <horiguchi.kyot...@lab.ntt.co.jp> wrote: > >> > >> I don't think it is not only on constatns. With the patch, > >> non-constants are .. getting a rather strange conversion. > >> > >> > >>> =# explain verbose select (a, b, c)::t1p1p1::t1p1::t1 from (select i, i * > >>> 2, i * 3 from generate_series(0, 10) i) x(a, b, c); > >>> QUERY PLAN > >>> ------------------------------------------------------------------------- > >> ... > >>> Output: (ROW(i.i, (i.i * 2), (i.i * 3))::t1p1p1)::t1 > >> > >> Conversions between scalar values cannot be assumed safely > >> composed each other for general inputs but it is known to be safe > >> for the ConvertRowtypeExpr case.. I think. > > > > I am not able to parse this statement. > > > > What output do you see without the patch? > > > > Without the patch, I see > explain verbose select (a, b, c)::t1p1p1::t1p1::t1 from (select i, i * > 2, i * 3 from generate_series(0, 10) i) x(a, b, c); > QUERY PLAN > -------------------------------------------------------------------------------------- > Function Scan on pg_catalog.generate_series i (cost=0.00..15.00 > rows=1000 width=32) > Output: ((ROW(i.i, (i.i * 2), (i.i * 3))::t1p1p1)::t1p1)::t1 > Function Call: generate_series(0, 10) > (3 rows) > > Only difference between the two outputs is direct conversion of t1p1p1 > row into t1 row, which is what is expected with this patch. Are you > suggesting that the optimization attempted in the patch is not safe? > If yes, can you please explain why, and give a scenario showing its > "un"safety?
I understood the reason for the current output. Maybe I meant the contrary, we can remove intermediate conversions more aggressively. I assumed that ::t1p1p1 and ::t1 yield the same output from any input. Is it right? regards. -- Kyotaro Horiguchi NTT Open Source Software Center
