Selecting Fields in Logical File

20 pts.
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Logical Files
PF
Physical File
If you would make a logical file and select only fields you need from a physical file that has 500,000 records it, Would it cause a performance issue when a record is updated in the PF?
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The performance issue is unchanged by the number of fields you map into the logical file.
The uses of a logical file with only a few of the fields might be restricted to only a small number of the processes that might need the key established by this logical. Requiring multiple logicals with the same key. Therefore, the use of the entire record structure is usually recommended.

Updates/inserts through such a logical can also lead to unexpected results.

Phil

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  • Gilly400
    Hi, If you're updating the PF, this should have very little impact on performance - logical files are in effect only indexes over the data in physical files and don't contain copies of the data. The index will only need to be updated if there's an impact on the key in the logical file. This will need to be done whether you select all the fields in the PF or one field in the PF. Regarding updates/inserts on such a logical - if you insert a record through a logical with only selected fields, the fields not selected in the LF will be filled with default values in the PF - this can cause problems for applications as some of these fields may have defaults of NULL values which many applications can't handle. With an update, only the fields selected in the LF are available for update within your application. Regards, Martin Gilbert.
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