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Vprocs


DEFINITION

Vproc, acronym for "Virtual PROCessor," is a self-contained instance of the processor software on a Teradata platform (SMP platform or a node). Vprocs are the basic units of parallelism that make up the Teradata database server.


OVERVIEW

To put it simply, a virtual processor is a simulated processor in a processing software system, or a software version of a dedicated physical processor. Each vproc uses a portion of the physical processor resource, and runs independently of other vprocs.  The vprocs co-existing within a node share a single memory pool - a collection of free memory in the node. The portion of memory allocated from the pool to one vproc will be returned to the pool after usage for use by other vprocs.

Vprocs are the basic units of parallelism that make up the Teradata database server. A single SMP node is made up of multiple vprocs, and a single Teradata MPP system is made up of multiple SMP nodes.  Vprocs run as multi-threaded processes to enable Teradata's parallel execution of tasks without using specialized physical processors.  They are labeled as "Virtual Processors" because they perform the similar processing functions as physical processors (CPU).

The concept of virtual processors is often utilized in the multithreading technology for parallel processing. Some examples are available from IBM Informix, HP POSIX and VM Host (HP-UX 11i) and SUN Solaris OS, though the concept is used differently in each case.

The concept of vprocs was introduced to Teradata to eliminate the need for proprietary technology in the form of physical processors. With Teradata V1 - the version used on DBC 1012, there were three types of physical processors:

    * The InterFace Processor(IFP) was responsible for the communication between the DBC and the HOST. Its components included parser, dispatcher, session controller, client interface and YNET interface.
    * The COmmunication Processor (COP) was the type of IFP that contained a gateway process for communication with hosts (DOS-PC/UNIX) via a network.     * The Access Module Processor (AMP) was the physical processing unit for all the Teradata database functions. Each AMP contained its own microprocessor, disk drive, file system, database software (Database Manager), Teradata Operating System (TOS), and YNET interface. In some sense, an AMP was a node.

The YNET Interconnection Network linked all the IFPs, COPs, and AMPs together with circuit boards and cables.

In Teradata V2, the above-mentioned physical processors (IFP, COP, and AMP) were replaced by Virtual PROCessors (vprocs), which were invented as an abstraction layer between the work-unit multithreading and the physical parallel processing system. [6] Logically, each vproc is a seperate AMP or PE instance within an SMP node. Physically, a vproc is a directly addressable collection of processes that allow data correction and fault tolerance. Teradata allocates its data rows across all AMP vprocs via hash partitioning. PE vprocs manage sessions, break work units down to multiple steps, make query plans and distribute the steps to the relevant AMP vprocs. The AMPs process the steps in parallel. Differently from Teradata V1, there may be multiple AMPs in a node.

To sum up, as Carrie Ballinger and Ron Fryer observe, "the VPROC is the fundamental unit of apportionment, and delivers basic query parallelism to all work in the system."


 
TYPES

There are two types of vprocs on the Teradata platform: AMP(Access Module Processor) and PE(Parsing Engine).

    * AMPs are the type of vprocs that contain a BYNET interface and perform database, file and disk functions.
    * PEs are the type of vprocs that handle session control, SQL parsing/optimizing, step generating and dispatching.



RELATED UTILITIES

Vproc Manager (vprocmanager)

Vproc Manager(vprocmanager) is used for the following administrative functions:
    * To check the status of the specific vproc or vprocs;
    * To alter the state of a vproc or the states for a series of vprocs;
    * To initialize and start the specific vproc - mostly an AMP vproc;
    * To initialize the file subsystem on the vdisk associated with a certain AMP vproc;
    * To force a manual database restart.

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