Skip navigation.

XTended Oracle SQL

Syndicate content
XTended Oracle SQL
Updated: 8 min 56 sec ago

RESULT_CACHE: run-time dependency tracking

Sun, 2015-07-05 13:20

As you know, since 11.2 “relies_on” clause was deprecated and oracle tracks dependencies at runtime now.
Test function and tables

create or replace function f_without_deps(p_tab varchar2) return varchar2
as
   res varchar2(30);
begin
   execute immediate 'select '''||p_tab||''' from '||p_tab||' where rownum=1' into res;
   return res;
end;
/
create table a as select 'a' a from dual;
create table b as select 'b' b from dual;
create view v_ab as select a,b from a,b;

[collapse]
And it works fine with normal tables:
v_ab

SQL> exec :p_tab:='v_ab';

PL/SQL procedure successfully completed.

SQL> call DBMS_RESULT_CACHE.flush();

Call completed.

SQL> select/*+ result_cache */ f_without_deps(:p_tab) result from dual;

RESULT
----------
v_ab

1 row selected.

SQL> select name,bucket_no, id,type,status,pin_count,scan_count,invalidations from v$result_cache_objects o order by type,id;

NAME                                                               BUCKET_NO  ID TYPE       STATUS     PIN_COUNT SCAN_COUNT INVALID
----------------------------------------------------------------- ---------- --- ---------- --------- ---------- ---------- -------
XTENDER.F_WITHOUT_DEPS                                                  1579   0 Dependency Published          0          0       0
XTENDER.V_AB                                                            3127   2 Dependency Published          0          0       0
XTENDER.B                                                                778   3 Dependency Published          0          0       0
XTENDER.A                                                                464   4 Dependency Published          0          0       0
select/*+ result_cache */ f_without_deps(:p_tab) result from dual       1749   1 Result     Published          0          0       0

[collapse]
But don’t forget that the result_cache also caches such functions with the objects, that usually should not be cached, and such objects will not be listed in the result_cache dependencies list:
v$database

SQL> exec :p_tab:='v$database';

PL/SQL procedure successfully completed.

SQL> call DBMS_RESULT_CACHE.flush();

Call completed.

SQL> select/*+ result_cache */ f_without_deps(:p_tab) result from dual;

RESULT
----------
v$database

1 row selected.

SQL> select name,bucket_no, id,type,status,pin_count,scan_count,invalidations from v$result_cache_objects o order by type,id;

NAME                                                               BUCKET_NO  ID TYPE       STATUS     PIN_COUNT SCAN_COUNT INVALID
----------------------------------------------------------------- ---------- --- ---------- --------- ---------- ---------- -------
XTENDER.F_WITHOUT_DEPS                                                   772   0 Dependency Published          0          0       0
PUBLIC.V$DATABASE                                                       1363   2 Dependency Published          0          0       0
select/*+ result_cache */ f_without_deps(:p_tab) result from dual       2283   1 Result     Published          0          0       0

3 rows selected.

[collapse] As you can see, there is only dependency on public synonym V$DATABASE, but not real base fixed X$-tables.
SYS.OBJ$

SQL> exec :p_tab:='sys.obj$';

PL/SQL procedure successfully completed.

SQL> call DBMS_RESULT_CACHE.flush();

Call completed.

SQL> select/*+ result_cache */ f_without_deps(:p_tab) result from dual;

RESULT
----------
sys.obj$

1 row selected.

SQL> select name,bucket_no, id,type,status,pin_count,scan_count,invalidations from v$result_cache_objects o order by type,id;

NAME                                                               BUCKET_NO ID TYPE       STATUS     PIN_COUNT SCAN_COUNT INVALID
----------------------------------------------------------------- ---------- -- ---------- --------- ---------- ---------- -------
XTENDER.F_WITHOUT_DEPS                                                  3922  0 Dependency Published          0          0       0
select/*+ result_cache */ f_without_deps(:p_tab) result from dual       3753  1 Result     Published          0          0       0

2 rows selected.

[collapse] The results were cached and the dependencies do not include system objects.
We easily check that the queries with any table in SYS schema or with sysdate,systimestamp,current_date,current_timestamp,dbms_random will not be cached:
SYS tables

SQL> select/*+ result_cache */ current_scn result from v$database;

    RESULT
----------
##########

1 row selected.

SQL> select name,bucket_no, id,type,status,pin_count,scan_count,invalidations from v$result_cache_objects o order by type,id;

no rows selected

SQL> explain plan for select/*+ result_cache */ * from sys.obj$;

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 2311451600

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      | 87256 |  7328K|   296   (1)| 00:00:04 |
|   1 |  TABLE ACCESS FULL| OBJ$ | 87256 |  7328K|   296   (1)| 00:00:04 |
--------------------------------------------------------------------------

[collapse] Note that there is no “RESULT CACHE” line.
And even if create own tables in SYS schema(don’t do it :)), they will not be cached :
SYS.V_AB

SYS> create table a as select 'a' a from dual;
SYS> create table b as select 'b' b from dual;
SYS> create view v_ab as select a,b from a,b;
SYS> grant select on v_ab to xtender;

XTENDER> explain plan for select/*+ result_cache */ * from sys.v_ab;
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------
Plan hash value: 215283502

-----------------------------------------------------------------------------
| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |      |     1 |     6 |     4   (0)| 00:00:01 |
|   1 |  MERGE JOIN CARTESIAN|      |     1 |     6 |     4   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL  | A    |     1 |     3 |     2   (0)| 00:00:01 |
|   3 |   BUFFER SORT        |      |     1 |     3 |     2   (0)| 00:00:01 |
|   4 |    TABLE ACCESS FULL | B    |     1 |     3 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement (level=2)

[collapse]
But sys_context and userenv will be cached successbully:
sys_context

SQL> explain plan for select/*+ result_cache */ sys_context('userenv','os_user')  from dual;

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------
Plan hash value: 1388734953

---------------------------------------------------------------------------------------
| Id  | Operation        | Name                       | Rows  | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |                            |     1 |     2   (0)| 00:00:01 |
|   1 |  RESULT CACHE    | 267m2hcwj08nq5kwxcb0nb2ka8 |       |            |          |
|   2 |   FAST DUAL      |                            |     1 |     2   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

Result Cache Information (identified by operation id):
------------------------------------------------------

   1 - column-count=1; attributes=(single-row); parameters=(sys_context);
        name="select/*+ result_cache */ sys_context('userenv','os_user')  from dual"

14 rows selected.

[collapse] userenv

SQL> explain plan for select/*+ result_cache */ userenv('instance')  from dual;

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------
Plan hash value: 1388734953

---------------------------------------------------------------------------------------
| Id  | Operation        | Name                       | Rows  | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |                            |     1 |     2   (0)| 00:00:01 |
|   1 |  RESULT CACHE    | dxzj3fks1sqfy35shbbst4332h |       |            |          |
|   2 |   FAST DUAL      |                            |     1 |     2   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

Result Cache Information (identified by operation id):
------------------------------------------------------

   1 - column-count=1; attributes=(single-row); parameters=(sys_context); 
       name="select/*+ result_cache */ userenv('instance')  from dual"

[collapse]

Categories: Development

A function gets called twice if the result_cache is used

Sun, 2015-07-05 07:37

Recently I showed simple example how result_cache works with non-deterministic functions and observed strange behaviour: a function gets fired once in the normal query, but twice with the result_cache hint.
Moreover, only third and subsequent query executions return same cached results as second query execution.
I didn’t want to investigate such behavior, just because 1) we should not cache the results of non-deterministic functions and 2) it doesn’t matter if we use deterministic functions.
But later I was asked to explain this, so this post is just a short description with test case.

Look at the simple function that just returns random values:

create or replace function f_nondeterministic(p int:=100) return int
as
  res number;
begin
   res:=round(dbms_random.value(0,p));
   return res;
end;
SQL> exec dbms_result_cache.flush;
PL/SQL procedure successfully completed.

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       481

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       689

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       689

with result_cache_statistics

SQL> exec dbms_result_cache.flush;

PL/SQL procedure successfully completed.

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       481

SQL> select name,value from v$result_cache_statistics where name in ( 'Create Count Success', 'Find Count');

NAME                                               VALUE
-------------------------------------------------- ----------
Create Count Success                               1
Find Count                                         0

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       689

SQL> select name,value from v$result_cache_statistics where name in ( 'Create Count Success', 'Find Count');

NAME                                               VALUE
-------------------------------------------------- ----------
Create Count Success                               1
Find Count                                         1

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       689

SQL> select name,value from v$result_cache_statistics where name in ( 'Create Count Success', 'Find Count');

NAME                                               VALUE
-------------------------------------------------- ----------
Create Count Success                               1
Find Count                                         2

SQL> select name,bucket_no, id,type,status,pin_count,scan_count,invalidations from v$result_cache_objects o;

NAME                                                BUCKET_NO         ID TYPE       STATUS     PIN_COUNT SCAN_COUNT INVALIDATIONS
-------------------------------------------------- ---------- ---------- ---------- --------- ---------- ---------- -------------
XTENDER.F_NONDETERMINISTIC                                552          0 Dependency Published          0          0             0
select/*+ result_cache */ f_nondeterministic(1000)       2102          1 Result     Published          0          2             0
 nondeter from dual

[collapse]
As you can see, second execution returns different result than first one.
If we change this function:

create or replace function f_nondeterministic(p int:=100) return int
as
  res number;
begin
   res:=round(dbms_random.value(0,p));
   dbms_output.put_line('fired! ('||res||')');
   return res;
end;

and repeat this test-case:

SQL> select/*+ result_cache */ f_nondeterministic(1000) nondeter from dual;

  NONDETER
----------
       943    -- << (2)

1 row selected.

fired! (607)    -- << (1)
fired! (943)    -- << (2)
SQL> /

  NONDETER
----------
       607    -- << (1)

1 row selected.

SQL> /

  NONDETER
----------
       607    -- << (1)

1 row selected.

SQL> /

  NONDETER
----------
       607    -- << (1)

1 row selected.

we will see that there were 2 function executions: first result was cached, and the second was fetched!

Categories: Development

SQL*Plus tips #7: How to find the current script directory

Fri, 2015-06-26 13:06

You know that if we want to execute another script from the current script directory, we can call it through @@, but sometimes we want to know the current path exactly, for example if we want to spool something into the file in the same directory.
Unfortunately we cannot use “spool @spoolfile”, but it is easy to find this path, because we know that SQL*Plus shows this path in the error when it can’t to find @@filename.

So we can simply get this path from the error text:

rem Simple example how to get path (@@) of the current script.
rem This script will set "cur_path" variable, so we can use &cur_path later.
 
set termout off
spool _cur_path.remove
@@notfound
spool off;
 
var cur_path varchar2(100);
declare 
  v varchar2(100);
  m varchar2(100):='SP2-0310: unable to open file "';
begin v :=rtrim(ltrim( 
                        q'[
                            @_cur_path.remove
                        ]',' '||chr(10)),' '||chr(10));
  v:=substr(v,instr(v,m)+length(m));
  v:=substr(v,1,instr(v,'notfound.')-1);
  :cur_path:=v;
end;
/
set scan off;
ho (rm _cur_path.remove 2>&1  | echo .)
ho (del _cur_path.remove 2>&1 | echo .)
col cur_path new_val cur_path noprint;
select :cur_path cur_path from dual;
set scan on;
set termout on;
 
prompt Current path: &cur_path

I used here the reading file content into variable, that I already showed in the “SQL*Plus tips. #1″.
UPDATE: I’ve replaced this script with a cross platform version.

Also I did it with SED and rtrim+ltrim, because 1) I have sed even on windows; and 2) I’m too lazy to write big PL/SQL script that will support 9i-12c, i.e. without regexp_substr/regexp_replace, etc.
But of course you can rewrite it without depending on sed, if you use windows without cygwin.

PS. Note that “host pwd” returns only directory where SQL*Plus was started, but not executed script directory.

Download latest version

Categories: Development

Little quiz: Ordering/Grouping – Guess the output

Tue, 2015-04-28 06:20

How many times have you guessed the right answer? :)
1

select * from dual order by -1;
select * from dual order by 0;

[collapse] 2

select *                   from dual                                     order by -(0.1+0/1) desc;
select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by -(0.1+0/1) desc;

[collapse] 3

select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by 0;
select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by 0+0;
select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by 3+7 desc;
select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by -(3.1+0f) desc;

[collapse] 4

select column_value x,10-column_value y from table(ku$_objnumset(5,4,3,1,2,3,4)) order by 1.9;
select column_value x,10-column_value y from table(ku$_objnumset(5,4,3,1,2,3,4)) order by 2.5;
select column_value x,10-column_value y from table(ku$_objnumset(5,4,3,1,2,3,4)) order by 2.7 desc;
select column_value x,10-column_value y from table(ku$_objnumset(5,4,3,1,2,3,4)) order by -2.7 desc;

[collapse]

Categories: Development

12c: Little test of “TABLE ACCESS INMEMORY FULL” with count stopkey

Mon, 2015-03-16 17:02

The table has 9M rows:

SQL> with function f return int is
  2       begin
  3          for r in (select value from v$mystat natural join v$statname where name like 'IM scan rows') loop
  4             dbms_output.put_line(r.value);
  5             return r.value;
  6          end loop;
  7       end;
  8  select f() from t_inmemory where rownum<=1
  9  ;
 10  /

       F()
----------
         0

1 row selected.

SQL> /

       F()
----------
    491436

1 row selected.

SQL> /

       F()
----------
    982872

1 row selected.
DDL and Plan
create table t_inmemory inmemory
as 
with gen as (select 0 id from dual connect by level<=3e3)
select 0 n from gen,gen;

SQL_ID  cpgrrfv9h6m52, child number 0
-------------------------------------
with function f return int is      begin         for r in (select value
from v$mystat natural join v$statname where name like 'IM scan rows')
loop            dbms_output.put_line(r.value);            return
r.value;         end loop;      end; select f() from t_inmemory where
rownum<=1

Plan hash value: 3697881339

----------------------------------------------------------------------------------
| Id  | Operation                   | Name       | Rows  | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |            |       |     3 (100)|          |
|*  1 |  COUNT STOPKEY              |            |       |            |          |
|   2 |   TABLE ACCESS INMEMORY FULL| T_INMEMORY |     1 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter(ROWNUM<=1)

[collapse]

Categories: Development