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Donald K. Burleson

Oracle Tips  

Number and Placement of Rollback Segments

Will the Tools Be Linked Single-Task or Be Independent (Two-Task)? 

This question deals with the way the Oracle tools, such as SQLLOADER, IMP, or EXP, address the Oracle kernel. See Figure 1.1 for a graphical demonstration of the concept of single-task versus a two- or multitask structure.

If the tools are linked single-task, they address a specific node’s Oracle kernel by default. To access another node or another system, a connect string must be used (connect strings will be covered in Chapter 14, Managing in a Distributed Environment). This mode is useful for a single-node database situation and saves on memory and task usage. This is generally used where a client/server architecture is not used. It has been demonstrated that relinking some tools single-task, such as the import and export utilities, will increase their performance by up to 30 percent.


Single-task linking will be allowed only in preOracle releases, so plan now to remove it from use.

If the tools are linked independent, or two-task, a connect string must always be used. It is called “two-task” because the tools must run as one task while the Oracle executable runs as another. Two-task is generally used in a client/server situation. This allows the following benefits:

Client machines to perform CPU-intensive tasks, offloading these tasks from the server.

* Movement of tools from one environment to another (such as from a development area to a production one) without relinking.
* The Oracle8i server to be relinked without relinking all of the tools.
* Two-task tools can reduce throughput, depending on the machine they are installed upon. The DBA needs to consider the costs versus the benefits when deciding whether to use single- or two-task-linked tools.

This is an excerpt by Mike Ault’s book “Oracle Administration & Management”.  If you want more current Oracle tips by Mike Ault, check out his new book “Mike Ault’s Oracle Internals Monitoring & Tuning Scripts” or Ault’s Oracle Scripts Download.




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