Permanent objects and access methods

 

The database objects and access methods used by the query engine can be broken down into three basic types of operations that are used to manipulate the permanent and temporary objects -- Create, Scan, and Probe.

The following table lists each object and the access methods that can be performed against that object. The symbols shown in the table are the icons used by Visual Explain.

Table 1. Permanent object's data access methods

Permanent objects	Scan operations	Probe operations
Table	Table scan	Table probe
Radix index	Radix index scan	Radix index probe
Encoded vector index	Encoded vector index symbol table scan	Encoded vector index probe

• Table
  An SQL table or physical file is the base object for a query. It represents the source of the data used to produce the result set for the query. It is created by the user and specified in the FROM clause (or OPNQRYF FILE parameter).

• Radix index
  An SQL index (or keyed sequence access path) is a permanent object that is created over a table and used by the optimizer to provide a sequenced view of the data for a scan or probe operation.

• Encoded vector index
  An encoded vector index is a permanent object that provides access to a table by assigning codes to distinct key values and then representing those values in a vector.

 

Parent topic:

Data access on DB2 UDB for iSeries: data access paths and methods