Hidden Oracle, part I: Exploring undocumented utilities

Corrected 29 September 2003

Each new release of Oracle brings new hidden utilities. They are sometimes used by internal Oracle development staff and left in Oracle for emergency support. Many of these undocumented utilities are very powerful but can be complex.

A hidden utility is not a utility that is physically hidden in the Oracle software. Rather, a hidden utility is an executable or PL/SQL package that is either undocumented or where the documentation is difficult to find. For example, some PL/SQL packages are never loaded by the Oracle installer, yet their definitions remain in the operating system files.

The main directories of interest regarding Oracle utilities are the following:

• $ORACLE_HOME/bin -- This contains the binary executables used by the Oracle server. Most of the tools discussed in this book reside here.
• $ORACLE_HOME/plsql/demo -- This contains a useful collection of SQL scripts related to many utilities, including dbms_profiler.
• $ORACLE_HOME/rdbms/admin -- This contains many SQL scripts used for creating PL/SQL packages and their required environments.
• $ORACLE_HOME/sqlplus/admin -- This contains scripts used with autotrace and other utilities.
• $ORACLE_HOME/otrace/admin -- This is the administration directory for the Oracle Trace diagnostic tool.
• $ORACLE_HOME/otrace/sysman -- This is used by utilities such as oemctl and the Oracle Management Server (OMS).
• $ORACLE_HOME/otrace/lib -- This contains facility files used with the oerr utility.

Many of these undocumented utilities such as TKPROF have surfaced from the obscure and entered mainstream Oracle toolkits while others remain hidden inside the O/S.

Finding hidden utilities

The easiest way to find hidden utilities is to look for new packages within Oracle. The following query compares the packages in Oracle8i with new packages in Oracle9i, using a database link:

select 
   object_name 
from 
   dba_objects@oracle9i 
where 
   owner      = 'SYS' 
and 
   object_type = 'PACKAGE BODY' 
minus
select 
   object_name 
from  
   dba_objects@oracle8i
where 
   owner     = 'SYS'
and 
   object_type = 'PACKAGE BODY';

This query will quickly display all package bodies owned by SYS that exist in Oracle9i but not in Oracle8i.

Finding hidden executables

dircmp -- s 
/u01/aoracle/product/8.1.7/bin 
/u01/oracle/product/9.0.3/bin

Here we compare the bin directory of 8.1.7 with Oracle 9.0.2. Note that the -- s option of the dircmp command tells UNIX to eliminate the matches from the output.

Hidden initialization parameters

Hidden initialization parameters are very dangerous because their use is undocumented, but they can be very valuable if you are careful. We can use a SQL*Plus query to quickly find any new initialization parameters in a new version of Oracle:

select 
   name
from 
    v$parameter@oracle9i 
minus 
select 
   name
from 
   v$parameter@oracle8i
; 

Every version of Oracle has special undocumented initialization parameters. These undocumented initialization parameters are usually only used in emergencies and only under the direction of a senior DBA or Oracle support. Because the undocumented parameters begin with an underscore "_", we can write a query against the X$ foxed tables to easily extract them:

COLUMN parameter           FORMAT a37
COLUMN description         FORMAT a30 WORD_WRAPPED
COLUMN "Session Value"     FORMAT a10
COLUMN "Instance Value"    FORMAT a10
SET LINES 100
SET PAGES 0
SPOOL undoc.lis

SELECT  
   a.ksppinm  "Parameter",  
   a.ksppdesc "Description", 
   b.ksppstvl "Session Value",
   c.ksppstvl "Instance Value"
FROM 
   x$ksppi a, 
   x$ksppcv b, 
   x$ksppsv c
WHERE 
   a.indx = b.indx 
   AND 
   a.indx = c.indx
   AND 
   a.ksppinm LIKE '/_%' escape '/'
/

Remember, not everyone knows about the undocumented parameters, and few know how or when to use them. Oracle does not allow DBAs to use many of these parameters unless specifically directed by Oracle support. DBAs should be aware that use of certain undocumented parameters will result in an unsupported system.

In many cases, the undocumented parameters were either documented in previous releases or will be in future releases. Of course, it is difficult to use the undocumented parameters that have never been documented, and never will be, safely. When in doubt, get guidance from Oracle support. We will take a closer look at some of these parameters in our next installment.

Hidden v$ views

New V$ views indicate a new functionality within the database, and not all of the views make it into the Oracle documentation. Here is a quick query to locate new views:

select 
   view_name
from 
    v$fixed_view_description@oracle9i 
minus 
select 
   view_name
from 
   v$fixed_view_description@oracle8i
; 

Hidden system events

With each new release of Oracle, system events and system statistics are changed. For example, here is a query to show changed system statistics for the database writer process between Oracle8i and Oracle9i:

sql> select distinct name from v$sysstat where name like 'DBWR%'


NAME
----------------------------------------------------------------
DBWR Flush object call found no dirty buffers
DBWR Flush object cross instance calls
DBWR buffers scanned
DBWR checkpoint buffers written
DBWR checkpoint write requests
DBWR checkpoints
DBWR cross instance writes
DBWR free buffers found
DBWR incr. ckpt. write requests
DBWR lru scans
DBWR make free requests
DBWR revisited being-written buffer
DBWR skip hot writes
DBWR summed scan depth
DBWR timeouts
DBWR transaction table writes
DBWR undo block writes

Here is the listing from Oracle9i. Note the changed statistics.

SQL> select distinct name from v$sysstat where name like 'DBWR%';

NAME
----------------------------------------------------------------
DBWR buffers scanned
DBWR checkpoint buffers written
DBWR checkpoints
DBWR cross instance writes
DBWR free buffers found
DBWR fusion writes
DBWR lru scans
DBWR make free requests
DBWR revisited being-written buffer
DBWR summed scan depth
DBWR transaction table writes
DBWR undo block writes

By the same token, we can use the v $event_name view to quickly locate all new system events in Oracle9i. Here is a quick query to locate new views:

select
   name
from
    v$event_name@oracle9i
minus
select
   name
from
   v$event_name@oracle8i
;

Undocumented SQL hints

Getting a list of Oracle hints for SQL tuning is often difficult. The Oracle hint list is inside the Oracle executable and you can extract the Oracle hint list easily with UNIX commands. In UNIX, you can use grep and strings to get them directly from the Oracle executable:

   strings $ORACLE_HOME/bin/oracle > hints.lst

Here are all of the 124 Oracle9i hints on release 9.0.2:

In this output we see 57 undocumented SQL hints:

These Oracle SQL hints can be extremely useful for solving complex SQL execution problems, and that is why Oracle created them. They generally remain undocumented because Oracle does not want someone with inadequate knowledge of optimizer internals using them because they could lead to confusing results. However, for the experienced SQL tuning professional these undocumented hints are a godsend.

Conclusion

In this first installment we have shown you how to extract powerful (but potentially dangerous) undocumented utilities, parameters, hints, packages and executables. Remember, many of these undocumented features have unknown effects and should be treated with great care.

In our next installment we will take a look at how the experienced Oracle professional can use undocumented features to improve Oracle performance.

References

• "Mike Ault's Oracle Internals Monitoring & Tuning Scripts." Mike Ault, 2003, Rampant TechPress
• "Oracle Utilities: Using Hidden Programs, Import/Export, SQL*Loader, Oradebug, Dbverify, Tkprof." Dave Moore, 2003, Rampant TechPress

About the Author

Don Burleson has more than 20 years of full-time DBA experience, and has written 32 books, including "Oracle high-performance SQL tuning" and most recently "Creating a Self-Tuning Oracle Database" published by Rampant TechPress. He has also published more than 100 articles in national magazines, serves as Editor-in-Chief of Oracle Internals magazine, and is owner of BEI Oracle Consulting.

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