This blog has moved here.

Monday, May 12, 2008

Profiling the new SIMPLE_INTEGER type

Oracle 11g comes with a new PLSQL type called SIMPLE_INTEGER. The official documentation says that this type yield significant performance compared to PLS_INTEGER type. Because I want to see this with my own eyes I’ve decided to test it using another new 11g component called hierarchical profiler which I also want to see how it’s working.

First of all, let’s setup the environment:

1. on the database server create a new directory to be used for creating profiler trace files:

oracle@obi:oracle$ mkdir profiler
oracle@obi:oracle$ chmod o-rx profiler/

2. create the DIRECTORY object in the database too, and grant read/write privileges to the testing user (in our case TALEK user):

SQL> create directory profiler_dir as '/opt/oracle/profiler';

Directory created.

SQL> grant read, write on directory profiler_dir to talek;

Grant succeeded.

3. grant execute privilege for DBMS_HPROF package to the TALEK user:

SQL> grant execute on dbms_hprof to talek;

Grant succeeded.

4. connect using TALEK user and create the following package (the only difference between the first and second approach is the type of the l_count variable):

create or replace package trash is

procedure approach_1;

procedure approach_2;

end trash;

create or replace package body trash is

procedure approach_1 as
l_count pls_integer := 0;
for i in 1..10000 loop
l_count := l_count + 1;
end loop;

procedure approach_2 as
l_count simple_integer := 0;
for i in 1..10000 loop
l_count := l_count + 1;
end loop;

end trash;

5. Profile the approaches:

SQL> exec dbms_hprof.start_profiling(location => 'PROFILER_DIR', filename => 'test.trc');

PL/SQL procedure successfully completed

SQL> exec trash.approach_1;

PL/SQL procedure successfully completed

SQL> exec trash.approach_2;

PL/SQL procedure successfully completed

SQL> exec dbms_hprof.stop_profiling;

PL/SQL procedure successfully completed

6. Analyze the generated trace file. For this we’ll use the "plshprof" command line utility.

oracle@obi:profiler$ plshprof -output report test.trc
PLSHPROF: Oracle Database 11g Enterprise Edition Release - Production
[8 symbols processed]
[Report written to 'report.html']

Aaaaand, the WINNER is:

TALEK.TRASH.APPROACH_1 -> 5713 (microseconds)
TALEK.TRASH.APPROACH_2 -> 100706 (microseconds)

Well… this is unexpected. According to Oracle docs, the SIMPLE_INTEGER should be faster. Ok, back to official doc: "The new PL/SQL SIMPLE_INTEGER data type is a binary integer for use with native compilation which is neither null checked nor overflow checked". Ahaaa… native compilation! Let’s check this:

SQL> show parameter plsql_code_type

------------------------------------ ----------- ------------------------------
plsql_code_type string INTERPRETED

So, we have a first clue and a first conclusion. If the database doesn’t use NATIVE compilation the SIMPLE_INTEGER type is actually much slower.

Let’s switch to native compilation. This can be easily done because the "plsql_code_type" parameter is dynamic:

SQL> alter system set plsql_code_type=native scope=both;

System altered.

It is important to compile once again the package because otherwise the old PLSQL byte code will be used (you can use "alter package trash compile plsql_code_type=native;"), then repeat the profiler tests.

The new results are:

TALEK.TRASH.APPROACH_2 -> 3927 (microseconds)
TALEK.TRASH.APPROACH_1 -> 12556 (microseconds)

Now, the second approach with SIMPLE_INTEGER is much faster and, interestingly, the PLS_INTEGER approach is slightly slower on native compilation compared with the same approach on the initial PLSQL interpreted environment.

Okey, one more thing. I really enjoy using the new 11g hierarchical profiler. From my point of view is a big step forward compared with the old DBMS_PROFILER, and the provided HTML reports produced by "plshprof" are quite lovely.

Sunday, May 11, 2008

WTF is that? (ep. 1)

I've just decided to put here some posts about the (...well, you know) Oracle WTF stories, those moments (... hours, and sometimes days) when being at my desk, I'm just staring at that stupid SQLPLUS> prompt couldn't figure out what the hell is happening.

Today, episode 1:

The scenario is very simple. I have two nice users: TALEK and SIM. TALEK has a table and gives UPDATE rights to SIM.

SQL> connect talek
Enter password:

SQL> create table muci (col1 varchar2(10));

Table created.

SQL> insert into muci values ('abc')
2 /

1 row created.

SQL> commit;

Commit complete.

SQL> grant update on muci to sim;

Grant succeeded.

SQL> connect sim
Enter password:

SQL> update talek.muci set col1='xyz' where col1='abc';
update talek.muci set col1='xyz' where col1='abc'
ERROR at line 1:
ORA-01031: insufficient privileges

Of course, this is the WTF moment. Why the UPDATE failed? The first thing to do is to check the DBA_TAB_PRIVS view for a confirmation that the UPDATE privilege is still there. (I'm pretty sure that no one was so fast to revoke meanwhile the granted privilege but, just in case...)

SQL> select grantee, owner, table_name, privilege 
from dba_tab_privs where table_name='MUCI' and owner='TALEK';

----- ----- --------- ----------

And yes, the privilege is there. Hmmm... what's next? Usually the next thought is that another Oracle bug makes fun of me. But, this sounds too scary to be true. Finally, the stupid answer comes to light.

SQL> show parameter sql92_security

------------------------------------ ----------- ------------------------------
sql92_security boolean TRUE

The database reference documentation says the following:
"The SQL92 standards specify that security administrators should be able to require that users have SELECT privilege on a table when executing an UPDATE or DELETE statement that references table column values in a WHERE or SET clause. SQL92_SECURITY specifies whether users must have been granted the SELECT object privilege in order to execute such UPDATE or DELETE statements."

With the above sql92_security parameter set, actually the "where col1='abc'" filter from the UPDATE statement complains about "insufficient privileges" and not the UPDATE itself. Without a filter the update executes as expected:

SQL> update talek.muci set col1='xyz';

1 row updated.

Ok, another lesson has been learned!

Friday, May 09, 2008

Obsolete Policy Violation

This is quite funny. Starting with 10g the LOG_ARCHIVE_START parameter is obsolete. Nevertheless, into the "Database Control" of a new installed 11g database I have a policy rule violation called "Use of Automatic Log Archival Features". The description of this policy rule says: "This policy ensures that archiving of redo logs is done automatically and prevents suspension of instance operations when redo logs fill. Only applicable if database is in archivelog mode".

Well, my database is already configured to run in archivelog mode:
SQL> archive log list
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 15
Next log sequence to archive 17
Current log sequence 17

So, where is the problem? The action suggested by "Database Control" console is "Set the value of the LOG_ARCHIVE_START initialization parameter to TRUE". Hmmm, that is to set an obsolete parameter... no, thanks!

Update: Actually, I discovered that there are a lot of non-relevant/obsolete policies for 11g, like SGA_TARGET is not used, or PGA_AGGREGATE_TARGET should be used etc. It seems that many default settings from the "Database Control" do not take into consideration the actual version of the managed database therefore you have to manually suppress these policy/rule violations.