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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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For example, if your system has 332 AMPs, the data imbalance between processors is ten percent; 323 AMPs will have 11 buckets, and nine AMPs will have 10 buckets.

If you have 608 AMPs, the data imbalance reaches 20%; 603 AMPs will have 6 buckets, and five AMPs will have five buckets.

Introduction to the Teradata RDBMS for UNIX

A-3
How the Teradata RDBMS for UNIX Differs from the Teradata RDBMS for TOS

Additional Specific Improvements

Enhanced Row Evaluation

File System Improvements

During a full file scan (a query for which the WHERE clause does not fully specify the value of an index), a large number of rows are read.

After each row is accessed, the RDBMS reinterprets the WHERE clause to determine if the row matches the conditions of the WHERE clause.

The Teradata RDBMS for UNIX provides the following enhancements to the row evaluation process:

• Executable vs. interpretive row evaluation.

If the number of rows to be accessed and interpreted is large enough, it becomes more efficient to compile the interpretive code into executable code, which can run up to 50 times faster. The Teradata RDBMS for UNIX always compiles this code during the parsing phase.

• Compile time (versus run time) operand typing and field offset calculation.

The Teradata RDBMS for UNIX evaluates data types and positions only once, at compile time, rather than repetitively, at run time.

• Common subexpression elimination.

Enhances the row evaluation process by eliminating the repetitive evaluation of the same subexpressions.

• NULL and compressed field access optimization.

Streamlined processes provide optimal evaluation of NULL values and compressed fields.

Many improvements have been made to the RDBMS file system, including the following:

• Automatic detection of cylinder fragmentation

• Uniqueness code carried in the cylinder index

• More efficient internal format of data blocks

• Larger maximum multi-row data block size (32 KB)

• Table-level attributes

• Optional look-ahead reads

• Optional page release

• User-tunable cache size for spool files

A-4

Introduction to the Teradata RDBMS for UNIX
How the Teradata RDBMS for UNIX Differs from the Teradata RDBMS for TOS

Additional Specific Improvements

Automatic Detection of Cylinder Fragmentation

Uniqueness Code Carried in the Cylinder Index

More Efficient Internal Format of Data Blocks

In the Teradata DBS for TOS, disk fragmentation is not realized until a data block or cylinder is not available for allocation.

Once realized for a data block allocation request, an attempt is made to migrate data blocks to an adjacent cylinder or a new cylinder altogether to make room available for the request.

For a cylinder allocation request, a mini-cylpack operation is done.

These operations can cause a significant delay to the query that is inserting the data.

The Teradata RDBMS for UNIX automatically performs a check for disk fragmentation.

Upon detection of fragmentation within a cylinder, a defragmentation task is scheduled to defragment the cylinder in the background.

In the case of fragmentation where the number of cylinders available for allocation is below a certain threshold, a background mini-cylpack task is scheduled to free up cylinders.

These operations as part of the automatic disk fragmentation detection significantly reduce the number of times that customer queries against databases are delayed due to disk fragmentation.

In the Teradata DBS for TOS, the cylinder index identifies the hash value associated with data blocks.

Because multiple data blocks can have the same hash value, a secondary lookup is required to read multiple data blocks until the block containing the desired row is found.

By indicating the uniqueness value associated with the first row in a data block, the cylinder index of the Teradata RDBMS for UNIX file system can be used to directly find the correct data block on a secondary index lookup (where the hash-id and uniqueness have already been determined), thereby reducing the number of blocks that have to be read to just one.

The internal format of data blocks includes two improvements:

• Search of block based on pointer array, allowing fast access within larger blocks

• Faster non-unique primary index access with large numbers of duplicates

Introduction to the Teradata RDBMS for UNIX

A-5
How the Teradata RDBMS for UNIX Differs from the Teradata RDBMS for TOS

Additional Specific Improvements

Larger Maximum MultiRow Data Block Size

Table-Level Attributes

In the Teradata DBS for TOS, data blocks with multiple rows are limited to 16KB in an NCR System 3600 and 8KB in an NCR DBC/1012 Model 4.

With the Teradata RDBMS for UNIX, the maximum size can be set at the system or table level to as much as 32K (less one sector).

The ability to adjust the size of the data blocks allows system administrators to fine tune the system for the type of workload desired.
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