Thursday, September 27, 2007
AS/400 F.A.Q's
DB2/400 & CL/400
1. How do you find physical file for a logical file?
By using DSPFD command and PFILE
2. What is use of RGZPFM? (Reorganize Physical File Member)
Remove deleted records to make the space occupied by them available for more records.
Reorganize the records of a file in the order in which you normally access them sequentially, there by minimizing the time required to retrieve records. This is done using the KEYFILE parameter.
This may be advantageous for files that are primarily accessed in an order other than arrival sequence. A member
can be reorganized using either of the following:
– Key fields of the physical file
– Key fields of a logical file based on the physical file
Reorganize a source file member, insert new source sequence numbers, and reset the source date fields (using the SRCOPT and SRCSEQ parameters on the Reorganize Physical File Member command).
Reclaim space in the variable portion of the file that was previously used by variable-length fields in the physical file format and that has now become fragmented
3. What is ODP in AS/400?
An open data path is the path through which all input/output operations
for the file are performed. In a sense, it connects the program to a file. If you do not specify the SHARE(*YES) parameter, a new open data path is created every time a file is opened. If an active file is opened more than once in the same job or activation group, you can use the active ODP for the file with the current open of the file. You do not have to create a new open data path.
4. Can you tell about the access path maintenance (*Immediate, *Rebuild, *Delay)?
The MAINT parameter specifies how access paths are maintained for closed files. While a file is open, the system maintains the access paths as changes are made to the data in the file.
Immediate maintenance of an access path means that the access path is maintained as changes are made to its associated data, regardless if the file is open. Access paths used by referential constraints will always be in immediate maintenance.
Rebuild maintenance of an access path means that the access path is only maintained while the file is open, not when the file is closed; the access path is rebuilt when the file is opened the next time. When a file with rebuild maintenance is closed, the system stops maintaining the access path. When the file is opened again, the access path is totally rebuilt. If one or more programs has opened a specific file member with rebuild maintenance specified, the system maintains the access path for that member until
the last user closes the file member.
Delayed maintenance of an access path means that any maintenance for the access path is done after the file member is opened the next time and while it remains open. However, the access path is not rebuilt as it is with rebuild maintenance. Updates to the access path are collected from the time the member is closed until it is opened again. When it is opened, only the collected changes are merged into the access path.
5. How do you update a file in a CL program?
By using RUNSQLSTM Command
6. What will be your approach in going either for OPNQRYF or Logical files?
7. What is a JOB?
Is a Unit of work or any piece of work within the business is considered a job
8. How to lock a file in CL?
Using ALCOBJ command
9. What is a MONMSG?
Using the Monitor Message (MONMSG) command, you can direct a procedure to
Take predetermined action if specific errors occur during the processing of the
Immediately preceding command. The MONMSG command is used to monitor for
Escape, notify, or status messages sent to the call stack of the procedure in which
The MONMSG command is used.
Free format RPG
MAKING THE TRANSITION TO FREE-FORMFree-form RPG is a controversial topic. I've received a number of messages from readers who feel strongly that I should provide my code samples in free-form RPG -- but I've also received messages from people who don't like it. Before starting to include free-form code in the newsletter, I thought it would be a good idea to introduce some of the aspects of free-form RPG to the readers. Unfortunately, I don't have nearly enough space to cover everything, so I will show some samples to get you started.
HOW TO CODE FREE-FORM STATEMENTSFree-form code only replaces the calculation specifications ("c-specs") of your program. The H,F,D,I,O, and P specs are still coded in the same way that they would be if you were writing traditional fixed-form code. Instead of coding a form type in position 6 of every record, free-form code is identified as a block. You code the "/free" compiler directive in position 7 of the record to start the block, and you code the "/end-free" compiler directive when you want the block to end. All free-form statements are typed in columns 8-80 of the record. Every free-form statement ends with a semi-colon. If no semi-colon appears at the end of a line of code, the compiler will assume that the statement is not finished and will interpret the next line as part of the same statement. The following is a very simple RPG program that uses free-form: D msg s 50A D wait s 1A /free eval msg = 'Hello World'; dsply msg ' ' wait; eval *inlr = *on; /end-free Just to make it absolutely clear -- the semi-colon ends every statement. It does not matter where one physical line begins and another ends. For example, the following statement is ugly, but perfectly valid: eval *inlr = *on; In free-form, the op-code is always specified first in each statement, followed by the factor1, factor2, and result fields. If a particular op-code does use the factor1, factor2, or result field, it is simply omitted. The following is a traditional C-spec for the chain op-code: C RRN chain MyFile This is the free-form equivalent: chain RRN Myfile;
THE EVAL AND CALLP OP-CODES ARE SPECIAL You do not have to specify an op-code when coding an EVAL or CALLP operation. The following lines of code are equivalent: eval msg = 'Hello World'; msg = 'Hello World';
MANY OP-CODES HAVE BEEN REMOVED One of the most controversial aspects of free-form RPG is that many of the op-codes that you have in traditional fixed-form RPG have been removed. For the most part, they were removed because of the expressions that you have available in the EVAL statement. The "Websphere Development Studio ILE RPG Reference" manual in the Information Center will tell you if an op-code is supported in free-form, and if not, it will suggest an alternative. For example, if you look up the TIME op-code in the manual, you'll see that it says: "Free-Form Syntax: (not allowed -- use the %DATE, %TIME, or %TIMESTAMP built-in function)"
SAMPLE FREE-FORM REPLACEMENTS In most cases where fixed-form op-codes were removed from free-form RPG, an expression or built-in-function (BIF) can be used instead. Most of the things that I'm going to explain here aren't only available in free-form and on the traditional C-specs using the EVAL op-code. Since RPG IV was introduced in V3R1, it has been possible to do math operations using expressions in the EVAL op-code. These same expressions work nicely in free-form. Here are some typical math operations: C A ADD B TOTAL1 C A SUB B TOTAL2 C A MULT B TOTAL3 C X DIV Y Z And this is how you'd code them as expressions: Total1 = A + B; Total2 = A - B; Total3 = A * B; Z = X / Y; Starting in V5R2, there are new operators in EVAL statements that can be used when performing a math operation that affects itself. C ADD 1 COUNT1 C SUB 1 COUNT2 C MULT 2 COUNT3 They can be coded with the special operators as follows: COUNT1 += 1; COUNT2 -= 1; COUNT3 *= 2; Prior to V5R2, you could accomplish the same thing by doing the following: COUNT1 = COUNT1 + 1; COUNT2 = COUNT2 - 1; COUNT3 = COUNT3 * 2; It's often useful to be able to get the remainder of a division operation. For example, if you want to know the remainder of X divided by Y, you'd traditionally code the following: C X DIV Y UNUSED C MVR R With the %REM() BIF, you no longer need to do division first -- and you no longer need to define a variable that you don't need elsewhere. You can simply code this: R = %REM(X : Y); The Z-ADD and Z-SUB op-codes were used in the old days to assign a numeric value to a variable. c z-add 15 A c
HOW TO CODE FREE-FORM STATEMENTSFree-form code only replaces the calculation specifications ("c-specs") of your program. The H,F,D,I,O, and P specs are still coded in the same way that they would be if you were writing traditional fixed-form code. Instead of coding a form type in position 6 of every record, free-form code is identified as a block. You code the "/free" compiler directive in position 7 of the record to start the block, and you code the "/end-free" compiler directive when you want the block to end. All free-form statements are typed in columns 8-80 of the record. Every free-form statement ends with a semi-colon. If no semi-colon appears at the end of a line of code, the compiler will assume that the statement is not finished and will interpret the next line as part of the same statement. The following is a very simple RPG program that uses free-form: D msg s 50A D wait s 1A /free eval msg = 'Hello World'; dsply msg ' ' wait; eval *inlr = *on; /end-free Just to make it absolutely clear -- the semi-colon ends every statement. It does not matter where one physical line begins and another ends. For example, the following statement is ugly, but perfectly valid: eval *inlr = *on; In free-form, the op-code is always specified first in each statement, followed by the factor1, factor2, and result fields. If a particular op-code does use the factor1, factor2, or result field, it is simply omitted. The following is a traditional C-spec for the chain op-code: C RRN chain MyFile This is the free-form equivalent: chain RRN Myfile;
THE EVAL AND CALLP OP-CODES ARE SPECIAL You do not have to specify an op-code when coding an EVAL or CALLP operation. The following lines of code are equivalent: eval msg = 'Hello World'; msg = 'Hello World';
MANY OP-CODES HAVE BEEN REMOVED One of the most controversial aspects of free-form RPG is that many of the op-codes that you have in traditional fixed-form RPG have been removed. For the most part, they were removed because of the expressions that you have available in the EVAL statement. The "Websphere Development Studio ILE RPG Reference" manual in the Information Center will tell you if an op-code is supported in free-form, and if not, it will suggest an alternative. For example, if you look up the TIME op-code in the manual, you'll see that it says: "Free-Form Syntax: (not allowed -- use the %DATE, %TIME, or %TIMESTAMP built-in function)"
SAMPLE FREE-FORM REPLACEMENTS In most cases where fixed-form op-codes were removed from free-form RPG, an expression or built-in-function (BIF) can be used instead. Most of the things that I'm going to explain here aren't only available in free-form and on the traditional C-specs using the EVAL op-code. Since RPG IV was introduced in V3R1, it has been possible to do math operations using expressions in the EVAL op-code. These same expressions work nicely in free-form. Here are some typical math operations: C A ADD B TOTAL1 C A SUB B TOTAL2 C A MULT B TOTAL3 C X DIV Y Z And this is how you'd code them as expressions: Total1 = A + B; Total2 = A - B; Total3 = A * B; Z = X / Y; Starting in V5R2, there are new operators in EVAL statements that can be used when performing a math operation that affects itself. C ADD 1 COUNT1 C SUB 1 COUNT2 C MULT 2 COUNT3 They can be coded with the special operators as follows: COUNT1 += 1; COUNT2 -= 1; COUNT3 *= 2; Prior to V5R2, you could accomplish the same thing by doing the following: COUNT1 = COUNT1 + 1; COUNT2 = COUNT2 - 1; COUNT3 = COUNT3 * 2; It's often useful to be able to get the remainder of a division operation. For example, if you want to know the remainder of X divided by Y, you'd traditionally code the following: C X DIV Y UNUSED C MVR R With the %REM() BIF, you no longer need to do division first -- and you no longer need to define a variable that you don't need elsewhere. You can simply code this: R = %REM(X : Y); The Z-ADD and Z-SUB op-codes were used in the old days to assign a numeric value to a variable. c z-add 15 A c
Iseries
SFLMSGKEY (Subfile Message Key) keyword for display files
Use this field-level keyword on the first field in the subfile record format for a message subfile (SFL and SFLMSGRCD keywords specified). It is not valid on the subfile control record format (SFLCTL). To select messages from a program message queue for display, your program places a message reference key in this field. Your program also places the name of the program message queue in the second field in the subfile record format. See SFLPGMQ (Subfile Program Message Queue) keyword for display files.
This keyword has no parameters.
This field is predefined as a four-position, character data type, hidden field. The following rules apply:
· This field must always be the first field defined in the subfile record format.
· The field name and SFLMSGKEY are the only DDS you can specify for this field.
Option indicators are not valid for this keyword or with the associated field.For more information on building and displaying message subfiles, see SFLPGMQ (Subfile Program Message Queue) keyword for display files
Use this field-level keyword on the first field in the subfile record format for a message subfile (SFL and SFLMSGRCD keywords specified). It is not valid on the subfile control record format (SFLCTL). To select messages from a program message queue for display, your program places a message reference key in this field. Your program also places the name of the program message queue in the second field in the subfile record format. See SFLPGMQ (Subfile Program Message Queue) keyword for display files.
This keyword has no parameters.
This field is predefined as a four-position, character data type, hidden field. The following rules apply:
· This field must always be the first field defined in the subfile record format.
· The field name and SFLMSGKEY are the only DDS you can specify for this field.
Option indicators are not valid for this keyword or with the associated field.For more information on building and displaying message subfiles, see SFLPGMQ (Subfile Program Message Queue) keyword for display files
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