in black and white
Main menu
Share a book About us Home
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics

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
Previous << 1 .. 58 59 60 61 62 63 < 64 > 65 66 67 68 69 70 .. 76 >> Next

As a general rule, systems used for heavy decision enabling support will benefit from using larger data block sizes.

Systems used for decision enabling support and some online transaction processing will have better performance with smaller data block sizes (the more OLTP performed, the smaller the data block size).

If a row is larger than the maximum multi-row data block size, it will be in a data block by itself; a single row data block can always be up to 32KB.

The Table Level Attribute feature allows you to set certain attributes at the table level.

Currently, this feature allows you to specify the maximum default size of the data blocks used to store the primary rows of a table, and the percentage of space to be left free on the cylinders consumed by a table during bulk data load operations.

You can use each attribute to improve performance and lower the consumption of resources, as follows:

• Data Block Size. This feature allows you to achieve optimum performance of the type of application that will most frequently access the table.

Decision support queries operate most efficiently on tables with large data block sizes because large blocks minimize the number of I/O operations involved.

Online transaction processing (OLTP) is most efficient on tables with a small data block size.

• Cylinder Percent of Free Space. This feature allows you to make the most efficient use of available disk space for decision support applications, and also improve the throughput of large DML applications.


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

Additional Specific Improvements

If the table is normally static and used for decision support

applications, then little or no free space (for example, 0%) is most efficient.

A table that will experience many inserts and thus grow rapidly should have a high percentage of free space. This will improve overall performance by reducing the need for cylinder splits and migrations.

Optional Look-Ahead Reads

The Teradata RDBMS for UNIX reads one block ahead during scans. By reading ahead, processing can be overlapped with I/O, improving performance for some workloads.

Note however that for other workloads it may be desirable to turn this feature off, as the aging of the data block may cause the block to be released from memory before it is accessed, thereby causing a waste of I/O.

Optional Page Release

In the Teradata DBS for TOS, a data block that has been accessed stays in memory until it ages out. The Teradata RDBMS for UNIX has an option which, when turned on, allows the system to immediately release data blocks once they have been accessed when it is unlikely that the data block will be accessed again in the nearterm, thereby releasing memory for other use.

Note that it is possible (but unlikely) that some workloads will perform better with this option turned off.

User-Tunable Cache Threshold for Data Block Caching

This Teradata RDBMS for UNIX feature allows the System Administrator to make tradeoffs between memory usage and I/O so that the workload for a system can be tuned for best performance.

Introduction to the Teradata RDBMS for UNIX

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

Additional General Improvements

Additional General Improvements

A number of general improvements have also been made to the Teradata RDBMS for UNIX. These improvements include the following:

• The aggregate cache has been increased to 96 KB, making it three times as large as the Teradata DBS for TOS aggregate cache (the V1 aggregate cache is 32 KB). This reduces row redistribution overhead when large aggregations are performed.

In addition, the performance of aggregations with a large number of groups has been significantly improved.

• The Teradata RDBMS for UNIX Optimizer has adjusted bit map sizes, reducing bit map collisions.

In the Teradata DBS for TOS, the Optimizer (which is used to minimize the I/O for certain types of table joins) is limited to 32KB.

The Teradata RDBMS for UNIX Optimizer has an adjustable bit map size (based on table statistics) that provides an effective use of the bit map without unnecessarily wasting memory.

• The Teradata RDBMS for UNIX has expanded parsing capabilities for complex queries.

• The Teradata RDBMS for UNIX has increased the information obtained by the Resource Usage (ResUsage) macros. ResUsage improvements include:

• A breakdown of I/O information by spool, transient journal, and data block

• More flexible logging intervals (Teradata DBS for TOS is limited to logging intervals of 6, 60, or 600 seconds)

• The information obtained can be specific to vprocs, nodes, or the entire system

• An improved hash function that eliminates the additive effect of multi-column indexes.

• New Teradata SQL features, including the following:

• Functions for investigating data row distribution, which allow the user to more effectively select a table's primary index. These functions are as follows:
Previous << 1 .. 58 59 60 61 62 63 < 64 > 65 66 67 68 69 70 .. 76 >> Next