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V8 Bundled Exec call – and Oracle Program Interface (OPI) calls

So, what he hell is that V8 Bundled Exec call which shows up in various Oracle 11g monitoring reports?!

It’s yet another piece of instrumentation which can be useful for diagnosing non-trivial performance problems. Oracle ASH has allowed us to measure what is the top wait event or top SQLID for a long time, but now it’s also possible to take a step back and see what type of operation the database session is servicing. 

I am talking about Oracle Program Interface (OPI) calls. Basically for each OCI call in the client side (like , OCIStmtExecute, OCIStmtFetch, etc) there’s a corresponding server side OPI function (like opiexe(), opifch2() etc). 

Creating Optimizer Trace Files

Many Oracle DBA’s are probably familiar with what Optimizer trace files are and likely know how to create them. When I say “Optimizer trace” more than likely you think of event 10053, right? SQL code like this probably is familiar then:

alter session set tracefile_identifier='MY_10053';
alter session set events '10053 trace name context forever';
select /* hard parse comment */ * from emp where ename = 'SCOTT';
alter session set events '10053 trace name context off';

In 11g, a new diagnostic events infrastructure was implemented and there are various levels of debug output that you can control for sql compilation. ORADEBUG shows us the hierarchy.

Full scans, direct path reads and ORA-8103 error hacking session video here (plus iTunes podcast address!)

I have uploaded the latest hacking session video to I have edited it a little, I cut out the part where I spilled an entire Red Bull onto my desk, with some onto my laptop (some keys are still sticky:)

Also, I do upload all these sessins into iTunes – so you can subscribe to my podcast! That way you can download the videos into your computer, phone or iPad. I have deliberately used 1024×768 resolution so it would look awesome on iPad screen! (so hopefully your commute time gets a bit more fun now ;-)



iTunes video-podcast:




How do you trouble-shoot a problem ? It’s not an easy question to answer when posed in this generic fashion; but perhaps it’s possible to help people trouble-shoot by doing some examples in front of them. (This is why I’ve got so many statspack/AWR examples – just reading a collection of different problems helps you to get into the right mental habit.)

So here’s a problem someone sent me yesterday. Since it only took a few seconds to read, and included a complete build for a test case, with results, and since it clearly displayed an Oracle bug, I took a look at it. (I’ve trimmed the test a little bit, there were a few more queries leading up to the error):

create table person (id number(2), name varchar2(10)) ;

insert into person values (1, 'Alpha') ;
insert into person values (2, 'Bravo') ;
insert into person values (3, 'Charlie') ;
insert into person values (4, 'Charles') ;
insert into person values (5, 'Delta') ;

create or replace view vtest as
select id, 'C' as letter from person where name like 'C%' ;

select,,, v.letter
from person p
left join vtest v on =
order by ;

The problem was that and gave different results – and the result was clearly wrong. So the question was: “is there something broken with outer joins on views, or possibly ANSI outer joins?” (The ansswer to the last question is always “probably” as far as I’m concerned, but I wouldn’t turn that into a “yes” without checking first.) Here are the two results:
        ID NAME               ID L
---------- ---------- ---------- -
         1 Alpha
         2 Bravo
         3 Charlie             3 C
         4 Charles             4 C
         5 Delta
        ID NAME               ID L
---------- ---------- ---------- -
         1 Alpha                 C
         2 Bravo                 C
         3 Charlie             3 C
         4 Charles             4 C
         5 Delta                 C

Clearly the extra ‘C’s in the letter column are wrong.

So what to do next ? Knowing that Oracle transforms ANSI SQL before evaluating an execution plan I decided to run the 10053 trace. Sometimes you get lucky and see the “unparsed SQL” in this trace file, a representation (though not necessarily 100% exact) image of the statement for which Oracle will generate a plan. I was lucky, this was the unparsed SQL (cosmetically enhanced):

	PERSON.ID  (+) = P.ID

So I ran this query, and found that the same error appeared – so it wasn’t about ANSI or views. So possibly it’s something about the CASE statement and/or the ROWID in the CASE statement, which I tested by adding three extra columns to the query:,

With these extra columns I got the following results from the query:

        ID NAME               ID NAME       ROWID              L L
---------- ---------- ---------- ---------- ------------------ - -
         1 Alpha                                               C
         2 Bravo                                               C
         3 Charlie             3 Charlie    AAAT7gAAEAAAAIjAAC C C
         4 Charles             4 Charles    AAAT7gAAEAAAAIjAAD C C
         5 Delta                                               C

So the CASE did the right thing with the column, but the wrong thing with the person.rowid column.
Time to get onto MOS (Metalink).

I searched the bug database with the key words: case rowid null
This gave me 2,887 hits, so I added the expression (with the double quotes in place) “outer join”
This gave me 110 hits, so from the “product category” I pick “Oracle Database Products”
This gave me 80 hits, and the first one on the list was:


The text matched my problem, so job done – except it’s reported as not fixed until 12.1

This isn’t a nice bug, of course, because the particular problem can be generated automatically in the transformation of ANSI outer joins to Oracle outer joins, so you can’t just change the code.

In passing, it’s taken me 31 minutes to write this note – that’s 10 minutes longer than it took to pin down the bug, but I have to say I got lucky on two counts: first, that the “unparsed SQL” was available, second that my choice of key words for MOS got me to the bug so quickly (which is where I usually find I waste most time).

Training Schedule for 2011 and Public Appearances

Online Seminars
A lot of people have asked me about whether I’d be doing any more seminars in the future. And the answer is yes – at least this year (might be too busy running a company the next year ;-)
I have finally put together the schedule for my 2011 seminars. In addition to the Advanced Oracle Troubleshooting seminar I will also deliver my Advanced Oracle SQL Tuning and Oracle Partitioning and Parallel Execution for Performance seminars, which I have done only onsite in past.
So, check out the seminars page:
Also don’t forget the Expert Oracle Exadata virtual conference next week!
Public Appearances

Oracle OpenWorld 2. October
  • I will talk about Large-Scale Consolidation onto Oracle Exadata: Planning, Execution, and Validation
  • Session ID 09355
Maybe I’ll lurk around the UKOUG venue as well in december ;-)

Enabling and Reading event 10046 / SQL Trace

As I’m done with the book and back from a quick vacation (to Prague, which is an awesome place – well, at least during the summer) I promised (in Twitter) that now I’d start regularly writing blog articles again. In a separate tweet I asked what to write about. Among other requests (which I’ll write about later), one of the requests was to write something about enabling and reading SQL trace files… 

I am probably not going to write (much) about SQL trace for a single reason – Cary Millsap has already written a paper so good about this topic, that there’s no point for me to try to repeat it (and my paper wouldn’t probably be as clear as Cary’s).

So, if you want to get the most out of SQL Trace, read Cary’s Mastering Performance with Extended SQL Trace paper:


The above link directs you to Method-R’s article index, as there’s a lot of other useful stuff to read there.

Wow, now I’m done with my first request – to write something about SQL Trace :-)


VirtaThon – Mining the AWR

Earlier I did a presentation at VirtaThon which is the same topic that I presented at Hotsos 2011.. Mining the AWR and Capacity Planning are very dear to my heart and up until now I’m using every research I did on that presentation to work on an “Exadata Provisioning Tool” which I’m planning to present at the next Hotsos 2012… well, the only thing that’s different this time is.. my attendees are virtual geeks all over the world ;)

Troubleshooting Oracle Exadata

The crew at My Oracle Support (MOS) [@myoraclesupport] have an excellent starting point for troubleshooting Oracle Exadata. I’d recommend to add this one to your MOS bookmarks.

Oracle Database Machine and Exadata Storage Server Information Center [ID 1306791.1]

Operating System Interaction

The excellent Madrid from the otn forums has a nice post here on a particular listener error caused by not following the install instructions precisely. I thought that I’d dig in a little further to illustrate the interplay between the O/S and our wonderful C program that is oracle.exe The message Hector got was   [...]

Another cache buffers chains latch contention troubleshooting example using LatchProf

One of my blog readers recently dropped me an email noting that he had noticed some cache buffers chains latch contention recently and successfully troubleshooted it with LatchProf. I asked if he’d like to blog about it and here’s the article:


Cache buffer chains latch contention typically shows up when some execution plans go bad, switching to nested loops or filter loops and revisiting the same table (or index) blocks very frequently…