Data stream information

Within an access plan, there is often a need to control the creation and flow of data from one series of operations to another. The data stream concept enables a group of operations within an access plan to be controlled as a unit.

The start of a data stream is indicated by the following statement in db2expln output:
   Data Stream n
where n is a unique identifier assigned by db2expln for ease of reference.
The end of a data stream is indicated by:
   End of Data Stream n

All operations between these statements are considered to be part of the same data stream.

A data stream has a number of characteristics, and one or more statements can follow the initial data stream statement to describe these characteristics:
  • If the operation of the data stream depends on a value that is generated earlier in the access plan, the data stream is marked with:
  • Similar to a sorted temporary table, the following statements indicate whether or not the results of the data stream will be kept in memory:
       Not Piped
    A piped data stream might be written to disk if there is insufficient memory at execution time. The access plan provides for both possibilities.
  • The following statement indicates that only a single record is required from this data stream:
       Single Record
When a data stream is accessed, the following statement will appear in the output:
   Access Data Stream n