2.76 FETCHCOMPS | FETCHLASTIMAGE
Valid for
Extract
Description
Use FETCHCOMPS or FETCHLASTIMAGE to extract full update images. When audit compression is used for a SQL table or Enscribe file, update operations to the table or file are recorded in a compressed format. Therefore, only part of the image is available for updates. (Full delete and insert images are always available). For some applications, this is acceptable. For example, when delivering the operation to another file, usually you need only the portion of the record that changed.
When either FETCHCOMPS or FETCHLASTIMAGE is specified, Extract attempts to retrieve the full record images of any compressed records from the original database using a SQL SELECT or Guardian READ statement.
You can fetch compressed images for selected files or tables. FETCHCOMPS and FETCHLASTIMAGE apply only to FILE or TABLE entries listed below the FETCHCOMPS or FETCHLASTIMAGE specification. Specify NOFETCHCOMPS or NOFETCHLASTIMAGE to turn off fetching for subsequent entries.
FETCHCOMP is more useful for audit applications, and FETCHLASTIMAGE is more appropriate for hot site applications. Several other items to note when using these parameters:
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FETCHLASTIMAGEoutputs the latest image of the record found on disk. Changes that occurred during the current transaction are ignored. -
FETCHCOMPSuses data from the latest image to fill in missing values in the compressed record. This approximates but is not always exactly the same as the actual transaction values (if subsequent updates occurred). -
If the original record has been deleted from the database, Extract discards the record from the compressed record with a warning message.
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The record retrieved may be a newer version than the record processed from the audit trail, so intermediate update information will be lost.
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Fetching each update from the database can result in significant performance penalties because each record must be fetched with random access into the database (Extract processes other updates sequentially).