Loading Using Unload/Load FAQS

1. What is the unload/load method for loading data into the staging area?
•  The unload/load method involves unloading data from the source database to a temporary flat file, then loading this file into the staging area. This method is often used when the source is on a remote server or when dealing with large volumes of data across heterogeneous technologies.
2. When should I use the unload/load strategy?
•  The unload/load strategy is particularly effective when dealing with large datasets and heterogeneous technologies. For example, you may unload data from a Microsoft SQL Server using bcp and load it into an Oracle staging area using SQL*Loader.
3. What are the steps involved in the unload/load method?
•  The steps typically involved in the unload/load method are:
1. Drop and create the loading table in the staging area.
2. Unload data from the source to a temporary flat file.
3. Generate the loading utility script to load the file into the staging area.
4. Execute the load command and check the return code.
5. Analyze log files for any errors.
6. Drop the loading table and remove the temporary file once the process is complete.
4. What utilities can be used for unloading data from the source?
•  For unloading data, you can use source database unload utilities, such as:

• bcp (Bulk Copy Program) for Microsoft SQL Server
• DB2 unload for IBM DB2
• Or the built-in OdiSqlUnload tool.

5. How is the unloading process done?
•  Data is unloaded from the source system to a temporary flat file using the appropriate unload utility (e.g., bcp, DB2 unload, or OdiSqlUnload).
6. What happens after the data is unloaded into the temporary file?
•  After unloading, a loading utility script (like SQL*Loader for Oracle) is generated to load the data from the temporary flat file into the loading table in the staging area.
7. What happens if an error occurs during the unloading or loading process?
•  If an error occurs, you can analyze the log files produced by the unloading or loading utility to identify the issue and handle it appropriately, ensuring the data load is successful.
8. Are there any issues with using the unload/load strategy?
•  Some challenges include:

• Extra disk space usage: Data is staged twice, once in the temporary file and again in the loading table.
• Efficiency concerns: This two-step process can be less efficient, especially when dealing with large datasets.

9. Can I use pipelines for the unload/load method?
•  A more efficient approach would be using file-based pipelines (FIFOs) between the unload and load utilities, but not all operating systems support this method.
10. Why is the unload/load method often preferred for large volumes of data?
•  The unload/load method is typically faster and more reliable for handling large volumes of data because it utilizes specialized utilities (like bcp and SQL*Loader) that are optimized for bulk data loading, making the process more efficient than row-by-row methods.