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Shannon -SETLL does NOT move any data or clear any buffers - it simply positions the file cursor to be ahead of the record containing the key value specified in the KLIST.
So, as far as efficiency goes, I'd say that the first example which uses SETLL (except using %EQUAL instead of %FOUND) will be much more efficient than using the CHAIN operation code, since CHAIN does perform I/O and if a record is not found it clears the buffer area.
- sjl----- Original Message ----- From: "Shannon O'Donnell" <shannon.odonnell@xxxxxxxxxxxxxx>
To: "RPG programming on the AS400 / iSeries" <rpg400-l@xxxxxxxxxxxx> Sent: Wednesday, February 28, 2007 1:27 PM Subject: CHAIN Versus SETLL and READ When Data Needed
midrange.com
I posed this question on MCPressOnline the other day but I would like to
get more opinions on it so I'll post it here too. A shop-standard
hangs in the balance.
Assume that you have an RPG program that has logic such that you need
to first see if some data is in a file, based on a key, and then if so,
you do something with that data.
Further assume that this file has a complex key with three fields.
The program logic is such that you check the maximum number of keys
for a match down to the minimum number of keys
Like this:
Key1 Klist
Kfld Fld1
Kfld Fld2
Kfld Fld3
Key2 Klist
Kfld Fld1
Kfld Fld2
Key3 Klist
Kfld Fld1
Which one of these logic blocks is most efficient?
Key1 Setll file
If %FOUND(file)
Key1 READE file
Use Fields
Else
Key2 Setll File
If %FOUND(file)
Key2 Use Fields
Else
Key3 Setll File
If %FOUND(file)
Key3 READE file
Endif
Endif
Endif
OR....
KEY1 Chain file
If %FOUND(file)
Use fields
Else
KEY2 Chain file
If %FOUND(file)
Use Fields
Else
KEY3 Chain file
If %FOUND(file)
Use Fields
Endif
Endif
Endif
My opinion is that the CHAIN is more efficient from both a
coding/maintenance standpoint and from an I/O standpoint, but I'm open
to opinions.
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