CCAPrint Newsletter for Model 204 and System 1032 Users

CCAPRINT: A Newsletter for Model 204^® and System 1032^® Users	July 10, 2003

System 1032

Lesser Known Features: Part 4
By Tym Stegner

In this edition of CCAPRINT, as part of my on-going series, I am highlighting the lesser-known features of System 1032 that support data integrity and data presentation.

Ensuring That System 1032 Data Is Reliable

A System 1032 dataset is a robust data storage medium that takes advantage of the data security features of the OpenVMS operating system. In addition, you can also ensure increased integrity of a dataset in System 1032 by using its own dataset journaling.

As part of a dataset definition, the JOURNAL command designates an external file where update transactions are managed. Before an update is executed on the dataset, System 1032 saves a copy of the disk blocks to be changed to the journal file and sets a checkpoint in the journal file for that update. A checkpoint is a place in a routine where enough information is stored to restart a computation or job run, if needed. The checkpoint contains the following information:

Checkpoint identification number
Username of the process issuing the update command
Date and time of the checkpoint posting
A damage notation, if System 1032 detected any damage since the last update

A dataset journal logs execution of the following commands:

ADD	ADMIT	ALLOCATE	APPEND
CHANGE	DELETE	DUMP DS_OUTPUT	INSERT
MODIFY	PREVENT	REMOVE	UNDELETE

Restoring a Dataset to a Valid State

The primary purpose of the journal file is to provide a way to return a dataset to a previously valid state. This capability is provided by the RECOVER command that can restore a damaged dataset back to:

A specific checkpoint
A savepoint
A specific time

During RECOVER processing, System 1032 displays the identification of all the checkpoints that precede the specified target checkpoint, in reverse chronological order. When finished, RECOVER processing truncates the journal and the damage history files, and clears the dataset’s current selection set.

Updates that followed the specified checkpoint or time are discarded. As journaling does not store any data about the actual updates, there is no way to roll a dataset forward after a recovery. The previous updates must be reapplied.

You can examine a dataset’s journal file using the SHOW JOURNAL INFORMATION command.

Using the Journal File

A dataset journal is activated only after the dataset is loaded. In addition, ADD commands are journaled after the ADD command has completed execution, not while it is processing. Adding multiple records via an ADD REPEATING command is treated as a single update event.

Non-update checkpoints can be posted using the SAVEPOINT command. A savepoint contains all the checkpoint information, plus a checkpoint name. Savepoints might be generated at the beginning of an update run, or at the beginning or end of a day. The SAVEPOINT command also has the option to purge a journal file by creating a new journal file, and creating an initial checkpoint.

Creating Readable, Logical Reports

To generate paged output to one or more files, reports in System 1032 are generally built on the PRINT command, often in conjunction with the PAGE and WRITE commands. These commands control the display or arrangement of the data at your terminal, on printer paper or address labels, or as simply stored in a file.

Controlling Column Spacing

The $PRNT_COLSPC system variable controls the default spacing between items specified in a PRINT command item list. The default value is two spaces. In situations where you need just a little more data on the line, you can set the system variable to one space. Note: you must reset the variable to two when you are done, if you want to maintain the default behavior. The space setting can be up to the limit of 127 spaces.

You can also use the LAYOUT option of the PRINT command to position columns. The LAYOUT default is relative spacing between items. By using the ABSOLUTE option, you can explicitly position each print item.

Assigning Page Numbers

System 1032 provides the PAGE command to perform page setup operations for an output channel. When a PAGE command is issued on a channel, the page number default is 1 and you may apply it to the page using the $PAGE system variable.

In some cases, such as when successive programs are writing to the same report file, you may want the page number to increase incrementally, instead of being reset by a new procedure. Use the INITIAL_PAGE option on a PAGE command to specify the starting page number.

Setting Page Margins and Breaks

The default page width for System 1032 is 80 columns. If you want to write a longer line, but do not want pagination on that channel, you can suppress the pagination on a channel by specifying PAGE LENGTH MISSING. Note that the MISSING keyword does not work with the PAGE SIZE option.

In the course of reporting, often you need to specify multiple blank lines or force a new page. While the WRITE FORMAT command offers means to accomplish these functions, additional options are provided by the OUTPUT command. The OUTPUT command can accept an integer variable to skip a varying number of lines or an integer constant can be used.

The OUTPUT SKIP PAGE command forces a page break. Odd or even pages are supported.

Formatting on the Fly

When creating reports, often additional output data is generated by WRITE commands within DO control blocks. The difficult part of presenting these additions is getting the newly output information to correctly line up with the print columns. Changes to the column formats do not propagate to the line formats used by the WRITE command.
However, using the TC and TV format specifiers, you can align the newly generated data with the appropriate print columns, thus eliminating the need to modify line formats, if column formats change.

Figure 1 illustrates the use of the TC format to align a dashed line at the end of the Length of Film column to indicate a summary. In the next WRITE command, the TV format is used to position and provide the column format for the calculated average timespan value.

Figure 1. Using the TC and TV formats in a WRITE command

1032> PRINT FILM LOF FORMAT TS4.7 BY FINAL DO AFTER
1032_       WRITE “--------------“ FORMAT( TC2 G)
1032_       WRITE “The average film length is” $AVE(LOF) –
1032_             FORMAT( G TV2 )
1032_       END_DO
              Film Title             Length of Film
-----------------------------------  --------------
Hamlet                                  2:35:00
The Bridge on the River Kwai            2:41:00
Lawrence of Arabia                      3:41:00
…                                       …
The Hireling                            1:48:00
                                     --------------
The average film length is              2:05:05

Another example of the use of TV formats can be found in the CCAPRINT article How do I line up my summary lines in System 1032 Reports?

In Summary

Journaling has become more popular, as disk sizes are now sufficient to accommodate journal files for frequently updated datasets. Sophisticated PRINT commands comprise some of the mainstays of data presentation in System 1032.

Coming Attractions

In the coming months, articles suggested by a review of lesser-known features will include:

The System 1032 Debugger
TRANGEN – a transact-command generator
System 1032 Record Descriptors
System 1032 Security