Free your thinking, free your code

I have been surprised, and a bit disappointed, to find many examples of RPG code in various social media groups still written in columns. This seems to perpetuate the stereotype of the "AS400" and "RPG programmers" held by many others who do not work with the IBM i, that we are working with an out of date language on an out of date platform.

The reality is different. IBM has spent many hundreds of millions of dollars on the IBM i operating system and PowerSystem servers to make this a modern platform and market leader, which can do so much more than the AS400 could. Part of these enhancements has been the introduction of free format RPG.

Using the Error Subfile for messages in display files

I recently received a communication asking me if there was an easier way to display messages on a display file than using a message subfile. In my opinion there is a much simpler way using the Error Subfile, ERRSFL, keyword in the display file.

I have been using the Error Subfile for many years, so long that I cannot remember when I first encountered it. By using it I do not have to add all the code for the message subfile to my programs. I can just enter ERRSFL into my display and let the operating system do the hard work.

Checking for locked objects in QDLS and IFS

In the past week one of my established jobs has started an "object locked" error. After some quick analysis I discovered that the object in question is a file in the QDLS file system. This left me asking myself a couple of questions

1. How can I see what is locking an object in QDLS?
2. Can I do the same for an object in the IFS?

Data Structures in CL

Data structures have always been a useful part of RPG, especially when returning information from a procedure. In CL I can create "Defined Variables", which are the equivalent of a RPG data structure. This becomes useful when I have a CL procedure that is called by RPG procedure, or vice versa. I will explain that in detail in a future post.

I am sure we have all encountered a situation where a data structure is passed to a CL program, and I have seen many programs were the subfields are broken out into individual variables using the Substring command, %SST. While this is easy if the data structure contains only character subfields, it can get messy if there are numeric subfields as I have to determine the start and end positions while considering the packing of the number.

Read operation code extenders

Operation code extenders on a Read operation in RPG are those letters that are follow the operation code in parentheses. I am sure the two most commonly known ones are:

read(e) TESTFILE ; reade(n) (KeyField) TESTFILE ;

Each one provides a little bit extra functionality that compliments the Read operation. On performing research for this post I found that with free format Read operations a number of additional extenders were added, some are available with only some of the Read operations in V5R4 and later releases.

The best way to find what is using all the disk space

Almost by accident I have started discussions on how to determine the largest objects on your IBM i server. I have given examples of how:

• Identify the 250 biggest objects using the DSPOBJD command, followed by a SQL statement, see here.
• Retrieve the number of deleted records/rows in files/tables, see here.

Discovering the number of deleted records in a file

In last week's post, here, I gave an example of how I determine the 250 biggest objects on my IBM i server. I created the information about the objects by using the Display Object Description command, DSPOBJD, and mentioned if anyone knew of a better way to get the same information to contact me.

Select the number of rows from SQL's result set

There are times when I do not want all of the rows/records from a table/file just, for example, the 100 with the largest value in a variable. I could use a "Copy File" command, CPYF, to copy on the first 100, but I cannot sort with a CPYF to select the largest. Fortunately SQL's Select does offer me a way to do this.

Today did not start well as the development server reached critical storage, 93%+ of DASD was being used. After doing some basic deleting and purging of a few files I was not able to lower the percentage of DASD more than 1%, which was not enough. What I need to do was to identify the largest object on this IBM i and determine if they could be deleted or their contents purged. But how to find those big objects?

Overriding control block size using SQL

Last week I discussed how to use control block size in the "Override with database file" command,OVRDBF, see here. In this post I am going to introduce the SQL procedure OVERRIDE_TABLE. Unlike the OVRDBF command this procedure can only do one thing, set the control block size for a table/file.

The OVERRIDE_TABLE appears to have introduced in IBM i 7.1 TR7. It is not mentioned in the IBM i 7.1 KnowledgeCenter website, but is in the 7.2 site.

This procedure has only three parameters:

Using control blocking to improve database performance

IBM i 7.1 TR7 saw an addition to the "Override with data base file" command, OVRDBF, the ability to set the control block size when performing file I/O. By increasing the control block size I can increase the memory allocated to the file's I/O buffer, which will increase the speed of I/O to the file. The enhancement is to the second element of the "Limit to sequential only" parameter, SEQONLY.

Limit to sequential only: Sequential only . . . . . . > ____ *NO, *YES Number of records . . . . . > _________ Number, *BUF32KB, *BUF64KB...

Using SQL to get information from Job Logs

I know I have written a lot recently about SQL, but IBM has added a lot of great views that allow you to access information easily. A good example is today's post: how to get information from a job log using SQL. Prior to this if you need to get information from the job log you had to use the RCVMSG command or the "List Job Log Messages" API, QMHLJOBL. Now I can get the information I want just using a SQL Select statement.

The JOBLOG_INFO table function was added to IBM i 7.2 and 7.1 TR9. It returns one row for each job log message, and what I really like about it is I can choose what information to return by using a WHERE clause in the Select statement.

Analyzing recursive data with SQL

This presentation was made by Birgitta Hauser, IBM i SQL expert, to Common Europe on May 28.