SQL, PL/SQL functions, and ORA-04091 table is mutating

Question

Dears,
Recently a question came up in an Oracle French forum about an insert/select that is throwing ORA-04091: table xxxx is mutating, trigger/function may not see it error in 11g while the same insert/select was working very well in 10g. The original poster gave a scenario that is easily reproducible. I am wondering what database release is correct the one throwing the error(11g) or the other one accepting the insert/select(10g)?
*10g*
mhouri.world > select * from v$version;
BANNER                                                                         
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi               
PL/SQL Release 10.2.0.4.0 - Production                                         
CORE     10.2.0.4.0     Production                                                     
TNS for Solaris: Version 10.2.0.4.0 - Production                               
NLSRTL Version 10.2.0.4.0 - Production                                         
mhouri.world > create table t_read_consistency (id number, vc varchar2(15), primary key (id));
Table created.
mhouri.world > insert into
  2        t_read_consistency
  3      select
  4        rownum id,
  5        rpad('a',15,'a')
  6      from
  7        dual
  8      connect by
  9        level<=1000;
1000 rows created.
mhouri.world > commit;
Commit complete.
mhouri.world > create or replace function f_read_consistency return varchar2
  2       as
  3        lv_vc  t_read_consistency.vc%type;
  4       begin
  5         select trc.vc
  6         into lv_vc
  7          from t_read_consistency trc
  8         where trc.id = 70 ;
  9        return lv_vc;
10     end f_read_consistency;
11    /
Function created.
mhouri.world >insert into
  2        t_read_consistency (id, vc)
  3      select
  4         1001
  5        ,f_read_consistency
  6      from dual;
      ,f_read_consistency
ERROR at line 5:
ORA-04091: table MHOURI.T_READ_CONSISTENCY is mutating, trigger/function may not see it
ORA-06512: at "MHOURI.F_READ_CONSISTENCY", line 5
_11g_
mohamed@mhouri> select * from v$version;
BANNER                                                                         
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production         
PL/SQL Release 11.2.0.1.0 - Production                                         
CORE     11.2.0.1.0     Production                                                     
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production                        
NLSRTL Version 11.2.0.1.0 - Production                                         
mohamed@mhouri> create table t_read_consistency (id number, vc varchar2(15), primary key (id));
Table created.
mohamed@mhouri> insert into
  2    t_read_consistency
  3  select
  4    rownum id,
  5    rpad('a',15,'a')
  6  from
  7    dual
  8  connect by
  9    level<=1000;
1000 rows created.
mohamed@mhouri>  create or replace function f_read_consistency return varchar2
  2   as
  3    lv_vc  t_read_consistency.vc%type;
  4   begin
  5     select trc.vc
  6     into lv_vc
  7      from t_read_consistency trc
  8     where trc.id = 70 ;
  9    return lv_vc;
10  end f_read_consistency;
11  /
Function created.
mohamed@mhouri> insert into
  2    t_read_consistency (id, vc)
  3  select
  4     1001
  5    ,f_read_consistency
  6  from dual;
  ,f_read_consistency
ERROR at line 5:
ORA-04091: table MOHAMED.T_READ_CONSISTENCY is mutating, trigger/function may
not see it
ORA-06512: at "MOHAMED.F_READ_CONSISTENCY", line 5 So far so good. Same behaviour for both releases. But let's bring a small change to the PL/SQL function to be as close as the example given in the French Forum
_10g where the select/insert was working without error_:
mhouri.world > select * from v$version;
BANNER                                                                         
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi               
PL/SQL Release 10.2.0.4.0 - Production                                         
CORE     10.2.0.4.0     Production                                                     
TNS for Solaris: Version 10.2.0.4.0 - Production                               
NLSRTL Version 10.2.0.4.0 - Production       
mhouri.world > create type t_read_cs as object (id number,vc varchar2(15));
  2  /
Type created.
mhouri.world > create type t_read_cs_tab  as table of t_read_cs;
  2  /
Type created.
mhouri.world > create or replace function f_read_consistency_tab
  2  return t_read_cs_tab
  3    as
  4      lc_t_read_cs_tab t_read_cs_tab := t_read_cs_tab();
  5      j  binary_integer := 0;
  6    begin
  7        for x in (select
  8                      id,
  9                      vc
10                   from  t_read_consistency trs
11                  where trs.id <= 10
12       ) loop
13 
14          j := j +1;
15          lc_t_read_cs_tab.extend;
16          lc_t_read_cs_tab(j) := t_read_cs(x.id, x.vc);
17     end loop;
18     RETURN lc_t_read_cs_tab;
19   end f_read_consistency_tab;
20  /
Function created.
mhouri.world > select count(1) from t_read_consistency;
  COUNT(1)                                                                                                             
      1000                                                                                                             
mhouri.world > select count(1)
  2  from (select * from table(f_read_consistency_tab));
  COUNT(1)                                                                                                             
        10                                                                                                             
mhouri.world > insert into t_read_consistency
  2         (id,vc)
  3      select id,vc
  4   from table(f_read_consistency_tab)
  5  ;
10 rows created.
mhouri.world > select count(1) from t_read_consistency;
  COUNT(1)                                                                                                             
      1010            
_11g where the same insert/select is throwing an error:_
mohamed@mhouri> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
mohamed@mhouri> create type t_read_cs as object (id number,vc varchar2(15));
  2  /
Type created.
mohamed@mhouri> create type t_read_cs_tab  as table of t_read_cs;
  2  /
Type created.
mohamed@mhouri> create or replace function f_read_consistency_tab
  2      return t_read_cs_tab
  3        as
  4          lc_t_read_cs_tab t_read_cs_tab := t_read_cs_tab();
  5          j  binary_integer := 0;
  6        begin
  7            for x in (select
  8                          id,
  9                          vc
10                      from  t_read_consistency trs
11                     where trs.id <= 10
12          ) loop
13 
14            j := j +1;
15             lc_t_read_cs_tab.extend;
16             lc_t_read_cs_tab(j) := t_read_cs(x.id, x.vc);
17        end loop;
18        RETURN lc_t_read_cs_tab;
19      end f_read_consistency_tab;
20    /
Function created.
mohamed@mhouri> select count(1) from t_read_consistency;
  COUNT(1)                                                                     
      1000                                                                     
mohamed@mhouri> select count(1) from (select * from table(f_read_consistency_tab));
  COUNT(1)                                                                     
        10                                                                     
mohamed@mhouri> insert into t_read_consistency
  2            (id,vc)
  3          select id,vc
  4      from table(f_read_consistency_tab)
  5     ;
    from table(f_read_consistency_tab)
ERROR at line 4:
ORA-04091: table MOHAMED.T_READ_CONSISTENCY is mutating, trigger/function may
not see it
ORA-06512: at "MOHAMED.F_READ_CONSISTENCY_TAB", line 7 In addition, one of the posters spotted out very judiciously that if we slightly change the definition of the table t_read_consistency in 11g, strangely the insert/select will work correctly in this data base as shown below:
ohamed@mhouri> drop table tr_read_consistency;
Table dropped.
mohamed@mhouri> create table tr_read_consistency
  2      as select rownum rn,
  3                trs.*
  4      from
  5         t_read_consistency trs;
Table created.
mohamed@mhouri> insert into tr_read_consistency
  2                 (rn, id,vc)
  3              select rownum, id,vc
  4           from table(f_read_consistency_tab);
10 rows created.So is this a regression? or a corrected bug during upgrade?
Thanks in advance
Mohamed Houri

Answer 1

I just followed the doc links provided by Tubby, which have 100% Correct answer. See below :
SQL> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
SQL> show user;
USER is "SCOTT"
SQL> create type t_read_cs as object (id number,vc varchar2(15));
  2  /
Type created.
SQL> create type t_read_cs_tab  as table of t_read_cs;
  2  /
Type created.
SQL> create table t_read_consistency (id number, vc varchar2(15), primary key (id));
Table created.
SQL> create or replace function f_read_consistency_tab
  2  return t_read_cs_tab
  3  as
  4  lc_t_read_cs_tab t_read_cs_tab := t_read_cs_tab();
  5  j  binary_integer := 0;
  6  begin
  7  for x in (select
  8  id,
  9  vc
10  from  t_read_consistency trs
11  where trs.id <= 10
12  ) loop
13  j := j +1;
14  lc_t_read_cs_tab.extend;
15  lc_t_read_cs_tab(j) := t_read_cs(x.id, x.vc);
16  end loop;
17  RETURN lc_t_read_cs_tab;
18  end f_read_consistency_tab;
19  /
Function created.
SQL> insert into
  2  t_read_consistency
  3  select
  4  rownum id,
  5  rpad('a',15,'a')
  6  from
  7  dual
  8  connect by
  9  level<=1000;
1000 rows created.
SQL> select count(1) from t_read_consistency;
  COUNT(1)
      1000
SQL> select count(1) from (select * from table(f_read_consistency_tab));
  COUNT(1)
        10
SQL> insert into t_read_consistency
  2  (id,vc)
  3  select id,vc
  4  from table(f_read_consistency_tab);
from table(f_read_consistency_tab)
ERROR at line 4:
ORA-04091: table SCOTT.T_READ_CONSISTENCY is mutating, trigger/function may not see it
ORA-06512: at "SCOTT.F_READ_CONSISTENCY_TAB", line 7
SQL> ed
Wrote file afiedt.buf
  1  create or replace function f_read_consistency_tab
  2  return t_read_cs_tab
  3  as
  4  lc_t_read_cs_tab t_read_cs_tab := t_read_cs_tab();
  5  j  binary_integer := 0;
  6  PRAGMA AUTONOMOUS_TRANSACTION; <--- This works as documented in 11.2.0.1
  7  begin
  8  for x in (select
  9  id,
10  vc
11  from  t_read_consistency trs
12  where trs.id <= 10
13  ) loop
14  j := j +1;
15  lc_t_read_cs_tab.extend;
16  lc_t_read_cs_tab(j) := t_read_cs(x.id, x.vc);
17  end loop;
18  RETURN lc_t_read_cs_tab;
19* end f_read_consistency_tab;
SQL> /
Function created.
SQL> insert into t_read_consistency
  2  (id,vc)
  3  select id,vc
  4  from table(f_read_consistency_tab);
insert into t_read_consistency
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.SYS_C0011307) violated
SQL> drop table t_read_consistency purge;
Table dropped.
SQL> create table t_read_consistency (id number, vc varchar2(15));
Table created.
SQL> insert into
  2  t_read_consistency
  3  select
  4  rownum id,
  5  rpad('a',15,'a')
  6  from
  7  dual
  8  connect by
  9  level<=1000;
1000 rows created.
SQL> commit;
Commit complete.
SQL> insert into t_read_consistency
  2  (id,vc)
  3  select id,vc
  4  from table(f_read_consistency_tab);
10 rows created.
SQL> commit;
Commit complete.
SQL>So, you have to add only PRAGMA AUTONOMOUS_TRANSACTION; before begin in your function code to avoid ORA-04091 in 11.2.0.1
But, All thanks to Tubby who pointed us to the correct documentation link.
Regards
Girish Sharma