Re: BUG #13541: There is a visibility issue when run some DDL and Query. The time window is very shot

The test cases is not clear in last mail,  the following shows all test
cases.
1. Table precondition
create table t(c1 int);
create table t2(c1 int):
insert into t values(1),(2),(3);
select xmin from t ;   (xmin=10043)
2. Step1:
   session1:  begin transaction isolation level repeatable read;
                 select * from t2;   (query on other table only for get
snapshot)
   Step2:
  session2: alter table t alter c1 set data type char(10);
               select xmin from t;   (new xid)
   Step3:
  session1:  select xmin from t;       (you can see 0 row, because the
snapshot is the same as the first query when transaction isolation level is
repeatable read.)

The DDL query(alter ...set data type ) rewrites all tuples with new
transaction xid,  so if the transaction isolation level is repeatable read,
that will cause wrong result.   Which DDL query rewrite all tuples with new
xid?




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