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Volume 10, Number 7 -- February 24, 2010

How To Use the Inhibit Write Keyword?

Published: February 24, 2010

Hey, Ted:

I stumbled upon the Inhibit Write (INHWRT) keyword parameter of the Override with Database File (OVRDBF) command recently while I was looking through the help text for something else. How long has the parameter been there? I can think of some ways to put it to work. Can you tell me something about INHWRT and how to go about using it?

--Bill


That parameter has been there forever, Bill, but I don't think a lot of people know about it. I see it mentioned occasionally in online forums. I don't consider it a terribly useful feature of i5/OS.

When you override a database file with INHWRT(*YES), the database manager suppresses all output operations to the file. To the best of my knowledge, the INHWRT parameter was designed with debugging in mind. When you enter debugging mode with STRDBG UPDPROD(*NO), the system halts if you try to write to a database file in a production database. By overriding the file with INHWRT(*YES), the debugger can run without writing to the file. However, if you can make a copy of the file in a test library, such as QTEMP, you won't need the override. Use the TYPE parameter of Create Library (CRTLIB) or Change Library (CHGLIB) to determine whether a library is for production or test.

Also, many shops now have a test system (often a logical partition), which means they can debug in production mode all the time. Such was not the case on the S/38 and earlier versions of the operating system currently known as IBM i.

If you use INHWRT in testing, be aware that your test may not be complete. For example, if the program tries to write a record with a duplicate key, your test run won't catch it if INHWRT is in effect. If you have calculations that are conditioned to the success or failure of output operations, they may not work the same under INHWRT(*YES) and INHWRT(*NO).

I know of two other ways to control output that you might consider when writing or modifying source code. You can use the EXTIND keyword in the F spec to control any file, input, as well as output. If an external indicator (U1-U8) is off when the cycle gets ready to open the file, the file will not be opened and all I/O will be ignored. I used that technique a good bit back in my S/34 and S/36 days.

The other way is control the file open and I/O operations manually. That is, pass a parameter into a program, and depending on the setting of that parameter, either process the file or not. You'll have to include the USROPN keyword on the file. This method is more work, but it's my preference.

All this is not to say that INHWRT is worthless. Many shops still run old programs that were written years ago. Imagine a program that builds a report and writes to a database file. Imagine that the report has gotten misplaced and needs to be regenerated. How do you rerun the program in order to get the report without corrupting the database file? Maybe you can use INHWRT(*YES).

And by the way, INHWRT also applies to output done though SQL.

--Ted




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TABLE OF CONTENTS
Naming Idiosyncrasies with the DB2 Storage Engine for MySQL

How To Use the Inhibit Write Keyword?

Hunting Down Storage Hogs

Four Hundred Guru

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