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:
```
   Correlated
```
Similar to a sorted temporary table, the following statements indicate whether or not the results of the data stream will be kept in memory:
```
   Piped
   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