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ENTDTALEN
Specifies the maximum field length of the entry-specific data
portion of the journal entry when the output file is created
by the system. This field contains part of the variable portion
of the journal entries (such as the after image of records for
update journal entries). If the output file exists, this
parameter is ignored.
The range of allowable values for this parameter is shown in
the table at the end of this parameter description.
A single value or a single list of three elements can be specified.
Single Values
*OUTFILFMT: The length of the entry-specific data field in the
output file depends on the value specified on the OUTFILFMT
parameter. The attributes of this field are the same as those
of the entry-specific data field in the corresponding
system-supplied model output file.
If *TYPE1 or *TYPE2 is specified on the OUTFILFMT parameter,
the entry-specific data field in the output database file will
be a fixed length field 100 characters in length.
If *TYPE3 or *TYPE4 is specified on the OUTFILFMT parameter, the
entry-specific data field in the output file is a variable-length
field with a maximum field length of 100 characters and an allocated
length of 100 characters. The buffer is 2 bytes longer than the
maximum field length to include the length portion of the
variable-length field.
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*CALC: The system calculates the length of the entry-specific data
field to accommodate the longest entry-specific data of all journal
entries in the specified receiver range. In this case, the entry-specific
data field is a fixed-length character field. The minimum length of the
field is 130 characters. If the length calculated by the system causes
the record format length to exceed the maximum record length, a message
is sent and the entry-specific data field is truncated. See the table
at the end of this parameter description for the possible maximum
record lengths of the various data types that can be specified.
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field-length: Specify the number of characters for the field length.
In this case, the field is a fixed-length character field. The maximum
value prevents the total record length of the output file from being
greater than the length allowed for physical database files. A
nonzero value is required by the system to ensure that the field
exists when the output file is created.
See the table at the end of this parameter description for the allowable
field lengths of the various data types that can be specified
Element 1: Variable-Length Field
To specify a variable-length field, specify *VARLEN for the first
element and length values for the last two elements (or let the
system use the default values).
*VARLEN: The entry-specific data field is a variable-length field.
This value can be specified only when OUTFILFMT(*TYPE3) or
OUTFILFMT(*TYPE4) is specified.
Element 2: Maximum Field Length
The maximum length of the variable-length, entry-specific data field.
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*CALC: The system calculates the maximum length of the entry-specific
data field to accommodate the longest entry-specific data of all
journal entries in the specified receiver range. The minimum length
of this field is 130 bytes. The corresponding buffer length
is 132 bytes: 130 bytes of data and 2 bytes for the length portion
of the variable-length field. [/color]
field-length: Specify the number of characters for the maximum
field length. See the table at the end of this parameter description
for the allowable field lengths of the various data types that can
be specified.
Element 3: Allocated Length
The allocated length of the variable-length entry-specific
data field.
*FLDLEN: The allocated length is the same as the maximum
length of the field.
allocated-length: Specify the number of characters for
the allocated length.
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If *CALC is specified for the second element and the system-calculated
maximum field length is smaller than the specified allocated length,
the allocated length is set to the maximum field length. If the
maximum field length is specified, the allocated length cannot
exceed the maximum field length. [/color]
Table 5. Range of Values for ENTDTALEN Parameter Output
File Format Entry- Specific Data Format Null Value Indicators Format
Entry Data Length Maximum Record Length
*TYPE1 Fixed Not applicable 1-32641 32766
*TYPE2 Fixed Not applicable 1-32611 32766
*TYPE3 Fixed Fixed 1-32596 32766
*TYPE3 Fixed Variable 1-32570 32740
*TYPE3 Variable Fixed 1-32570 32740
*TYPE3 Variable Variable 1-32568 32738
*TYPE4 Fixed Fixed 1-32596 32766
*TYPE4 Fixed Variable 1-32570 32740
*TYPE4 Variable Fixed 1-32570 32740
*TYPE4 Variable Variable 1-32568 32738
Note: When the file contains variable-length fields, the maximum
record length does not include the 2 bytes per variable-length field.
***More Information***
After all these years, journaling is still a seldom-used and rarely understood
feature of OS/400-i5/OS and its integrated database, DB2 UDB for iSeries
formally DB2/400). Many sites simply don't know how to set it up properly
to perform its chief function of providing another level of data protection.
Here, and in the next few installments, we'll discuss what journaling is,
how it works, and how to set it up to give you the greatest level of
data protection.
What journaling is and how it works
Journaling, generally speaking, is a process of recording activity. In accounting,
it is the process of recording financial activity -- monies in and monies out.
On the iSeries, journaling refers to the process of recording object activity.
Journaling on the iSeries typically involves the recording of the activity related
to files, namely, physical files. When a file is being journaled, activity such as
file-opens, file-closes and data updates are recorded. For example, when a program
writes out a new record or updates an existing one, the system makes an entry in
the associated journal. The entry contains such information as the job name and
program name that made the change(s) to the file, as well as a copy of the record
that was changed. (Note: Journaling can be configured to record a copy of the
record before it is changed and/or to record a copy of the record after it
is changed.)
How to set up journaling in three easy steps
Create one or more journal receivers. Use the Create Journal Receiver (CRTJRNRCV)
command to create a journal receiver. Think of the journa as a notebook binder and
the journal receiver as the pages (i.e., the notebook paper where information is written).
The journal receiver is where the journal entries are actually recorded. The journal
"connects" the receiver to the file. It's a good habit to name the journal receiver
the same as the journal, plus a numeric suffix such as 0 or 1. (See the next step
on what to name the journal.) Also, you should put journal receivers in the
same library as the file. (This is very important in order to simplify recovery
procedures, which we will discuss in Part III.) For maximum protection, consider
storing the journal receiver in a different ASP than the file so that their storage
will not be on the same disk unit.
Create a journal. Use the Create Journal (CRTJRN) command to create a journal and
specify the receiver created in step 1. Although you can journal multiple files to
the same journal (and, in some cases, that is actually preferable), you will generally
want to have a journal "serving" a single file. A good practice is to name the journal
the same as the file and put it in the same library as the file, but store it in the
same ASP as the journal receiver.
Start journaling the file. This is done by using the Start Journal Physical File
(STRJRNPF) command. This is how you associate a file to a journal. Once the association
is made, the system will record in the journal receiver a copy of any record added,
updated or deleted from the file. Other activity, such as when the file is opened
and closed, can also be recorded in the journal receiver if you choose by selecting
the appropriate options on the STRJRNPF command.
For more information on the journal commands mentioned above and other journal-related
commands, please see the subsequent section "Quick reference to journaling commands."
Four basic journal entry categories
The most common journal entries fall into four basic categories. Each category is
represented by a one-character code (shown in parenthesis in the following list).
Within each category are a number of different journal entry types. Each journal
entry type is represented by a two-character entry code (also shown in parenthesis
within the category descriptions below).
Journal and journal receiver operations (J). These include such things as references
to the previous receiver (PR) or the next receiver (NR) in a chain. Also, at IPL-time,
an entry is made (e.g., an IN entry for IPL after normal end) marking a critical
chronological boundary in the file activity.
File operations (F). This category includes file opens (OP) and file closes (CL).
Record operations (R). Record updates (UP), deletes (DL), and new records written
(PT and PX) all fall into this category.
Commitment control (C). Anything related to commitment control falls into this category.
Some examples are begin commitment control (BC),
start a commit cycle (SC), commit operation (CM)
and rollback operation (RB).
There are other categories and entry types in addition to those listed above. However,
those are what you will come across most often. For a complete listing, see the
documentation or online help.
Quick reference to journaling commands
APYJRNCHG. Uses the journal entries to apply changes that have occurred since a
database file was saved or some other specified time.
CHGJRN. Use this command to change the attributes of a journal or to attach new journal
receivers to a journal.
CMPJRNIMG. This command compares and lists the difference between the before-image and
after-image of a record, or between the current after-image of a record and
the previous after-image of the record.
CRTJRN. Use this command to create a journal.
CRTJRNRCV. Use this command to create a journal receiver.
DLTJRN. Use this command to delete a journal.
DLTJRNRCV. Use this command to delete a journal receiver.
DSPJRN. This command displays or prints the journal entries that are in the journal
receivers associated with the specified journal. This command has outfile
support so you can list the journal entries to a database output file for
further processing or analysis.
DSPJRNRCVA. Use this command to display the attributes of a journal receiver.
ENDJRNPF. This command ends journaling for the specified physical file.
RCVJRNE. This command allows a specified user program to continuously receive
journal entries one at a time as they are written to the journal.
The behavior is similar to an exit program.
RMVJRNCHG. Use this command to remove changes that have occurred to a database
file from a specified point in time to some previous point in time
(allowed only if before-images were recorded during the time).
RTVJRNE. Use this command to retrieve a journal entry and place it in CL
program variables.
SNDJRNE. Use this command to write user-defined entries to a journal
(i.e., journal receiver).
STRJRNPF. Use this command to start journaling for the physical file.
WRKJRN. This command displays a menu from which you can perform many
journal-related functions, such as system-assisted recovery of
journaled files.
WRKJRNA. This command displays the attributes of a journal and the
associated receivers.
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