When a client initiates index building, sorting, or logical
recovery, the database server creates multiple threads to work on
the task in parallel, using as much of the computer resources as possible.
While one thread is waiting for I/O, another can be working.
In the following cases, virtual processors of the CPU class can
run multiple session threads, working in parallel, for a single client:
Index building
Sorting
Recovery
Scanning
Joining
Aggregation
Grouping
User-defined-routine (UDR) execution
For more information about parallel UDR execution, see Informix® User-Defined Routines and
Data Types Developer's Guide.
The following figure illustrates parallel processing. Figure 1: Parallel processing