Distributed query optimization feature - Definition - Oracle Distributed Database concepts

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• Nirja Shah   -Posted on 21 Sep 15
  - Application development in a distributed system raises issues that are not applicable in a non-distributed system.
  
  - Transparency in a Distributed Database System
  - With minimal effort, you can develop applications that make an Oracle Database distributed database system transparent to users that work with the system.
  - The goal of transparency is to make a distributed database system appear as though it is a single Oracle Database.
  - Consequently, the system does not burden developers and users of the system with complexities that would otherwise make distributed database application development challenging and detract from user productivity.
  
  - Remote Procedure Calls (RPCs)
  - Developers can code PL/SQL packages and procedures to support applications that work with a distributed database.
  - Applications can make local procedure calls to perform work at the local database and remote procedure calls (RPCs) to perform work at a remote database.
  
  - Distributed Query Optimization
  - Distributed query optimization is an Oracle Database feature that reduces the amount of data transfer required between sites when a transaction retrieves data from remote tables referenced in a distributed SQL statement.
  - Distributed query optimization uses cost-based optimization to find or generate SQL expressions that extract only the necessary data from remote tables, process that data at a remote site or sometimes at the local site, and send the results to the local site for final processing. - This operation reduces the amount of required data transfer when compared to the time it takes to transfer all the table data to the local site for processing.
  - Using various cost-based optimizer hints such as DRIVING_SITE, NO_MERGE, and INDEX, you can control where Oracle Database processes the data and how it accesses the data.

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