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Introduction to the Teradata® RDBMS for UNIX® Version 2 Release 2.1 - NCR

NCR Introduction to the Teradata® RDBMS for UNIX® Version 2 Release 2.1 - NCR, 1998. - 315 p.
Download (direct link): inntroduktionteradata1998.pdf
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9 gncApply passes the concrete steps to the Dispatcher.

The Dispatcher controls the sequence in which steps are executed. It also passes the steps to the BYNET (or Vnet on single node systems) to be distributed to the AMP database management software.

Note that AMP steps can be sent in any one of the following ways:

• Between one PE and one AMP using the hashing algorithm

• Among a selected group of AMPS (referred to as a dynamic BYNET (or Vnet) group

• Among all AMPs in the system.

Stage Process
1 The Dispatcher receives concrete steps from gncApply.
2 The Dispatcher places the first step on the BYNET (or Vnet)— the Dispatcher tells the BYNET whether the step is for one AMP, several AMPS, or all AMPS—and waits for a completion response. Whenever possible, the Teradata RDBMS performs steps in parallel to enhance performance.
3 The Dispatcher receives a completion response from one or several AMPS and places the next step on the BYNET. It continues to do this until all the AMP steps associated with a request are done.

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Introduction to the Teradata RDBMS for UNIX
Teradata RDBMS Architecture

The Parsing Engine

The Dispatcher controls the sequence in which steps are executed Dispatching the Steps 2 and passes the steps onto the Vnet (single node systems) or BYNET

(multinode systems). Once the steps are handed over to the Vnet or BYNET, they are referred to as AMP steps. The Dispatcher tells the Vnet or BYNET whether an AMP step is for one AMP, a group of AMPs, or all AMPs.

When the Dispatcher receives a completion response from an AMP or AMPs, the Dispatcher sends the next step via the Vnet or BYNET until all of the AMP steps associated with a request are complete.

The Vnet or BYNET software controls the transmission of messages to and from the AMPs. See Figure 2-3, where 12 rows of a table are distributed among disks attached to four AMPs.

If a request is for a single row, the PE transmits steps to a single AMP, as shown at PE 1 in Figure 2-3. If the request is for many rows (an all-AMP request), the PE causes the Vnet or BYNET to broadcast the steps to all AMPs as shown at PE 2 in Figure 2-3 . To minimize system overhead, the PE can send a step to a subset of AMPs.

Figure 2-3 PE Routing of Teradata SQL Request Messages


Disk Disk Disk Disk
R1, R5, R9 R2, R6, R10 R3, R7, R11 R4, R8, R12
, ,

HD14A001

Introduction to the Teradata RDBMS for UNIX 2-15

AMP 1 AMP 2 AMP 3 AMP 4
Teradata RDBMS Architecture

The Parsing Engine

Processing the Steps

As an example, consider the following two Teradata SQL statements from a table of checking account information:

1.SELECT * FROM Table_01 WHERE AcctNo = 12 9317 ; 2.SELECT * FROM Table_01 WHERE AcctBal > 1000 ;

In this example:

• PEs 1 and 2 receive requests 1 and 2.

• The data for account 129317 is contained in table row R9 stored on AMP 1

• Information about all account balances is distributed evenly among the disks of all four AMPs

The PE 1 Parser determines that its request is a primary-index retrieval, which calls for access and return of one specific row.

The Dispatcher in PE 1 then issues a message to the Vnet or BYNET containing an appropriate read step and R9/AMP 1 routing information. Once the desired record is received from AMP 1, PE 1 transmits the data back to the TDP.

The PE 2 Parser determines that this is an all-AMPs request, then issues a message to the Vnet or BYNET containing the appropriate read step to be broadcast to all four AMPs.

Once results are received from the AMPs, PE 2 transmits the data back to the TDP.

To enhance system performance, the RDBMS executes steps in parallel whenever possible.

Parallel steps can work with multi-statement requests, macros, and single statements and can provide a significant improvement in response time.

For example, the response time of a multi-statement request consisting of four statements that can be independently executed may be cut in half.

The AMPs are responsible for obtaining the rows required to process the request.

The software on the AMPs does the following:

• Processes AMP steps by performing select, insert, delete, and update operations on the data on the disks.

• Performs other functions associated with AMP steps such as journaling, space accounting, index maintenance, and output data conversion.

• Performs utilities to configure and reconfigure the RDBMS. (See Chapter 5, “Database Administration” for more information.)

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Introduction to the Teradata RDBMS for UNIX
Teradata RDBMS Architecture

The Parsing Engine

• Uses the file system software to perform primitive physical data block operations.

An AMP step can be sent in one of the following ways:

• Between one PE and one AMP using hashing algorithm.

• Among a selected set of AMPs, called a dynamic Vnet or BYNET group.

• Among all AMPs in the system.

An AMP step is broadcast to all AMPs when a full-table scan is requested or when the operation uses nonunique secondary indexes (NUSIs).
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