Archive for January, 2012

How to get full list of the Oracle hidden parameters?

Oracle has many hidden parameters. You will not find them in V$PARAMETER or see them with SHOW PARAMETERS command as these are hidden. All these parameter start with “_” (underscore), like _B_TREE_BITMAP_PLANS.
These parameters are undocumented. You won’t find them in Oracle documentation. These parameters are for specific purpose only. Some of them are OS specific and used in unusual recovery situations. Some are also used to enable\disable new feature. You should be very much careful while using them. Please check with Oracle Support before changing them.

Here is a simple SQL query that you can use to find these parameters:

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 '/'
Categories: Oracle, RDBMS Tags: , ,

BITMAP CONVERSION (FROM/TO) ROWIDS – SQL query execution plan steps.

Recently, in one of the database I support, I was notified that one of the SQL query worked very slow. I checked SQL execution plan and discovered two steps: BITMAP CONVERSION TO ROWIDS and BITMAP CONVERSION FROM ROWIDS which looked suspicious to me because there are no bitmap indexes in that database.
The “BITMAP CONVERSION TO ROWIDS” or “BITMAP CONVERSION FROM ROWIDS” execution plan steps were generally introduced in Oracle 9i when the default value for the hidden parameter _B_TREE_BITMAP_PLANS changed from FALSE to TRUE. The “BITMAP CONVERSION” plan is not always an optimal step when converting from b-tree indexes, and it can be very inefficient access plan in some cases. Bitmap conversion to ROWIDS does not require bitmap indexes, and it’s sometimes found in cases of SQL with complex WHERE clause conditions.
The bitmap conversion to rowids is sometimes seen with star transformations, so you could start with changing the initialization parameter STAR_TRANSFORMATION_ENABLED to FALSE. In my case it didn’t help, so I had to change the hidden parameter _B_TREE_BITMAP_PLANS to FALSE.
You can also turn off bitmap conversion at the session level, for testing:

alter session set _b_tree_bitmap_plans=false;

As always, notify Oracle technical support before changing any hidden parameters, as they can make your database unsupported.

Desktop icons in Windows 2008 R2.

Have you noticed that you cannot add the desktop icons (Computer, Network, etc.) to your Windows Server 2008 R2 desktop? Am I the only one who is annoyed by this? If not, here’s how to get them back.

First, you’ll have to go into Server Manager and access the Features section. In Features, you will select to add a feature and then select the Desktop Experience feature. Once added, you will have to reboot the server. That’s right! A reboot is required to add icons to your desktop.

Now this is really insane. Think about it. You can add your own icons for shortcuts on the desktop, but to get Computer and Network, you have to add the entire Desktop Experience feature. What a ridiculous decision Microsoft made here.

Now that I’ve expressed my suffering, we shall move on.

Once you’ve rebooted the server, simply right-click on the Desktop and select Personalize. From here, you can add the desktop icons you desire as usual.

That’s should be all.

Enable multiple RDP connections per user in Windows Server 2008.

In Windows Server 2003 you could have multiple Remote Desktop session with the same user. In Windows Server 2008 this is not possible by default. If you login with the same user account the first session will be taken over by second session.

There are several (at least 4 methods to change this), here are two of them:
Method 1.
Allow multiple Remote Desktop sessions per user by changing a registry key.
1. Click Start, then Run and type regedit.
2. Check out the following registry key:


3. If the fSingleSessionPerUser value doesn’t exist, create a new DWORD value named fSingleSessionPerUser.
4. Open the fSingleSessionPerUser value. The possible values for this setting are as follows:
– 0x0 Allow multiple sessions per user
– 0x1 Force each user to a single session

Method 2.
1. Click Start, then Run and type tsconfig.msc.
2. You should untick the Restrict each user to a single session option.

That’s should be all.

Categories: MS Windows, OS Tags: , , ,