Oracle7 Server Distributed Systems Volume I: Distributed Data
SQL Statement Execution in a Distributed System
SQL statement execution of remote and distributed statements is essentially the same in a distributed system as in a non-distributed database. However, depending on the type of statement issued, the location of statement execution can vary.
Remote Queries and Updates
All remote queries and remote updates are sent to the remote node for statement execution. The remote node executes the statement and returns any results back to the local node, which returns them to the user or application.
Distributed Queries and Distributed Updates
The statements in a procedure or trigger that constitute a distributed update are sent individually to the correct remote node for execution. Results are returned to the local node and then to the calling
user or application.
Values for Environmentally-
Dependent SQL Functions
In a distributed system, environmentally-dependent SQL functions, such as SYSDATE, USER, UID, and USERENV, are evaluated always with respect to the local node regardless of where the statement (or portion of a statement) is executed. The USERENV function is supported only for queries.
Shared SQL for Remote and Distributed Statements
The mechanics of a remote or distributed statement using shared SQL are essentially the same as those of a local statement. The SQL text must match, the referenced objects must match, and the bind types of any bind variables must be the same. If available, shared SQL areas can be used for the local and remote handling of any statement (or decomposed query).
Optimization of SQL Statements in a Distributed System
The optimization approach available for SQL statements can vary depending on the type and complexity of the statement.