回复：BUG #15766: discard plans bug. database CRASH

Thank you , it's likely a bug caused by pg_hint_plan extension , it's not a pg's bug.
i comment the pg_hint_plan , and will not crash now.

```
#shared_preload_libraries = 'oracle_fdw,pg_hint_plan' # (change requires restart)
restart pg.

postgres=# prepare a(int) as select * from tf where id=$1;
PREPARE
postgres=# \d tf
Table "public.tf"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+--------------------------------
id | integer | | not null | nextval('tf_id_seq'::regclass)

postgres=# execute a(1);
id
----
(0 rows)

postgres=# insert into tf values (1);
INSERT 0 1
postgres=# insert into tf values (2);
INSERT 0 1
postgres=# execute a(1);
id
----
1
(1 row)

postgres=# alter table tf add column c1 int;
ALTER TABLE
postgres=# execute a(1);
ERROR: cached plan must not change result type
postgres=# \set VERBOSITY verbose
postgres=# execute a(1);
ERROR: 0A000: cached plan must not change result type
LOCATION: RevalidateCachedQuery, plancache.c:723
postgres=# discard plans;
DISCARD PLANS
postgres=# execute a(1);
ERROR: 0A000: cached plan must not change result type
LOCATION: RevalidateCachedQuery, plancache.c:723
postgres=# execute a(1);
ERROR: 0A000: cached plan must not change result type
LOCATION: RevalidateCachedQuery, plancache.c:723
```

best regards,
digoal.
------------------------------------------------------------------
发件人：Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
发送时间：2019年4月18日(星期四) 01:09
收件人：digoal <digoal(at)126(dot)com>
抄　送：pgsql-bugs <pgsql-bugs(at)lists(dot)postgresql(dot)org>
主　题：Re: BUG #15766: discard plans bug. database CRASH

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> PostgreSQL version: 11.1

> discard plans bug. database CRASH

This seems to be fixed already; I just get additional reports of

ERROR: cached plan must not change result type

in all branches. I didn't go through the git logs to try to
identify the relevant fix, so possibly it was post-11.2.

regards, tom lane