Managing the order of the alternate keys in an indexed file
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Sometimes when a user accesses a file migrated from Acucobol or RM/COBOL to either Jisam or c-tree file systems, the order of the alternate keys can change from the previous COBOL dialect used.
In these cases or even when we created a brand new file, it's important to use the appropriate compiler options for handling alternate keys.
When migrating from ACU to Jisam or c-tree or accessing an original file by using Visionj file connector, make sure you compile the program with '-cko' option.
This compiler option lists keys in offset order. Without this option keys are listed following the order they're declared in the FILE-CONTROL paragraph.
There is a similar compiler option, '-crko', specific to RM/COBOL data files. Just like '-cko', without this option keys are listed following the order they're declared in the FILE-CONTROL paragraph. But '-crko' handles split keys with multiple segments differently.
The -crko will evaluate all segments of the key for the offset, while -cko only evaluates the first segment for the offset.
Note that the -cko and -crko options change the order in which keys are registered in the physical file (you can verify this with file management utilities such as jutil and ctutil). As a consequence, this option affects XML/ISS dictionaries as well as the I$IO and file interfaces where keys are indicated by ordinal number.
Here's an example. The attached program, create-file.cbl, will create a file called "songs" with three alternae keys. The keys are declared in the file-control paragraph this way:
select songs assign to "songs"
organization is indexed
access is dynamic
record key is sr-key
alternate record key is key2 = sr-artist sr-genre sr-album duplicates
alternate record key is key3 = sr-artist sr-album sr-genre duplicates
alternate record key is sr-title duplicates
file status is file-status.
And the order of the items in the FD is:
fd songs.
01 songs-record.
05 sr-key.
10 sr-id pic 9(5).
05 sr-data.
10 sr-title pic x(30).
10 sr-length pic x(5).
10 sr-artist pic x(20).
10 sr-album pic x(30).
10 sr-genre pic x(15).
10 sr-label pic x(30).
10 sr-year pic 9(4).
10 sr-authors occurs 5.
15 sr-author pic x(20).
Attached is a sample program that can be used to see the results of using the two different compiler options or none of them.
- When compiled without any option, the order of the keys would be: sr-key, key2, key3, sr-title.
- With -cko, the order is changed to follow the order of the fields in the FD: sr-key, sr-title, key2, key3.
- With -crko, the order is changed to follow the order of the fields in the FD also for segments: sr-key, sr-title, key2, key2.
To see this in detail, compile the program with -cko or -crko and without any option, run it to create the file songs, and look at the file with jutil, using the -x option to display the offsets:
jutil -info songs -xThe structure of the physical file including all the alternate keys with the length and the offset of each alternate key are:
With no compiler options:
Key Dups Segments
1 N 1 Seg. Offset Size
1 0 5
2 Y 3 Seg. Offset Size
1 40 20
2 90 15
3 60 30
3 Y 3 Seg. Offset Size
1 40 20
2 60 30
3 90 15
4 Y 1 Seg. Offset Size
1 5 30
With -cko:
Key Dups Segments
1 N 1 Seg. Offset Size
1 0 5
2 Y 1 Seg. Offset Size
1 5 30
3 Y 3 Seg. Offset Size
1 40 20
2 90 15
3 60 30
4 Y 3 Seg. Offset Size
1 40 20
2 60 30
3 90 15
With -crko:
Key Dups Segments
1 N 1 Seg. Offset Size
1 0 5
2 Y 1 Seg. Offset Size
1 5 30
3 Y 3 Seg. Offset Size
1 40 20
2 60 30
3 90 15
4 Y 3 Seg. Offset Size
1 40 20
2 90 15
3 60 30