The onunload and onload utilities provide the fastest way to move data, but they do not let you modify the database schema or move from one operating system or database server version to another. The onunload utility unloads data from the specified database or table onto a tape or a file on disk in disk-page-sized units, making this utility more efficient than dbexport. The onload utility takes a tape or a file that the onunload utility creates and re-creates the database or the table. The onunload and onload utilities are faster than dbimport, dbload, or LOAD but are much less flexible.
Because the data is written in page-sized units, you can use onunload and onload only when certain constraints are met. For example, you cannot use onunload and onload to move data between UNIX and Windows. You can, however, use the onunload and onload utilities to move data between computers that use the same database server on the same platform.
You can only use onunload and onload if your answer to each of the following questions is yes. If your answer is no, you cannot use onunload and onload.
| Use onunload and onload If Your Answer To Each Question Is Yes |
|---|
| Do you want to move to another database server of the same version? |
| Do you want to move data between GLS and non-GLS databases? |
| Do you want to modify the database schema? |
| Do you want to move an entire database or an entire table? |
| Are the page images compatible? Are the numeric representations the same? Is the target database server on the same hardware platform? |
The onunload and onload utilities are the fastest way to unload and load data, but you can use them only when all the following criteria are the same for the source and target computers:
You cannot use onunload and onload to move data between UNIX or Linux and Windows because they use different page sizes. For example, the page size is two kilobytes on some UNIX systems and four kilobytes on Windows.
You can use the onunload and onload utilities to unload from and load data into the following database servers between computers that have the same operating system:
For example, your site purchases a more powerful UNIX computer to allow faster access for users. You need to transfer existing databases to the new database server on the new computer. Use onunload to unload data from the first database server and then use onload to load the data into the second database server. Both database servers must have the same version number, or they must have compatible version numbers. You can move an entire database or selected tables only, but you cannot modify the database schema.
The onunload and onload utilities have the following restrictions:
Do not use onunload and onload to move data between two Dynamic Server 10.0, 9.40, 9.30, or 9.2x databases if either database contains an extended data type.
Use the HPL instead to move the data.
You can use onunload and onload to move data between databases if the NLS and GLS locales are identical. For example, if user A has a French locale NLS table on server A and tries to load data into a German locale GLS table on server B, onload and onunload report errors. However, if both the NLS and GLS tables were created with the same French locale, onload and onunload would work.
The tape that onload reads contains binary data that is stored in disk-page-sized units. For this reason, the computers where the original database resides (where you use onunload) and where the target database will reside (where you use onload) must have the following characteristics:
If the page sizes are different, onload fails. If the alignment or numeric data types on the two computers are different (for example, with the most-significant byte last instead of first or different float-type representations), the contents of the data page could be misinterpreted.
For additional constraints and restrictions, see The onunload and onload Utilities.
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