DataStage官方培训教程7
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Module Objectives
Upon module completion, students will be able to: Define what a hashed file is List different types of hashed files List various uses for hashed files Create hashed files Source hashed files Use caching attributes to accelerate reads and writes Import metadata from hashed files Delete hashed files
What is a Hashed File?
A DataStage file written to the file system Most use a hashing algorithm based on key
column values Files can be cataloged in the project’s VOC file for
Ascential Software Corporation 50 Washington Street
Westboro, MA 01581-1021 USA Phone: (508) 366-3888 Fax: (508) 366-3669
Ascential, DataStage, INTEGRITY, MetaRecon, MetaStage and MetaBroker are trademarks of Ascential Software Corporation. Pick is a registered trademark of Pick Systems. Ascential Software is not a licensee of Pick Systems. Other trademarks and registered trademarks are the property of the respective trademark holder.
Uses of Hashed Files
Good for locally storing tables of a remote database that will be read from frequently
Good as an intermediate file location in sequences of jobs
DataStage官方培训教程7
This document and the software described herein are the property of Ascential Software Corporation and its licensors and contain confidential trade secrets. All rights to this publication are reserved. No part of this document may be reproduced, transmitted, transcribed, stored in a retrieval system or translated into any language, in any form or by any means, without prior permission from Ascential Software Corporation.
Copyright © 2003 Ascential Software Corporation. All rights Reserved
Ascential Software Corporation reserves the right to make changes to this document and the software described herein at any time and without notice. No warranty is expressed or implied other than any contained in the terms and conditions of sale.
easy retrieval
Types of Hashed Files
21 different types Type 1 and 19 do not use a hashing algorithm Types 2-18 are static hashed files and use a
hashing algorithm Type 25 is static and uses a B-tree algorithm Type 30 is dynamic and uses a hashing algorithm
Main use is as a reference lookup table
Hashing Algorithms (Static File Types)
Character type
Location where most variation occurs in key column
Right
Middle
Left
Any
Wholly numeric
2
6
10
14
Numeric & separators
3
ASCII
4
Any
5
7
11
15
8
Fra Baidu bibliotek
12
16
9
13
17
Inserting Records into Hashed Files
Hashing Algorithm
Group 1 Group 2 Group 3 Group 4 Group 5
Overflow Groups
When there is not enough space remaining in a group, the group overflows
Module Objectives
Upon module completion, students will be able to: Define what a hashed file is List different types of hashed files List various uses for hashed files Create hashed files Source hashed files Use caching attributes to accelerate reads and writes Import metadata from hashed files Delete hashed files
What is a Hashed File?
A DataStage file written to the file system Most use a hashing algorithm based on key
column values Files can be cataloged in the project’s VOC file for
Ascential Software Corporation 50 Washington Street
Westboro, MA 01581-1021 USA Phone: (508) 366-3888 Fax: (508) 366-3669
Ascential, DataStage, INTEGRITY, MetaRecon, MetaStage and MetaBroker are trademarks of Ascential Software Corporation. Pick is a registered trademark of Pick Systems. Ascential Software is not a licensee of Pick Systems. Other trademarks and registered trademarks are the property of the respective trademark holder.
Uses of Hashed Files
Good for locally storing tables of a remote database that will be read from frequently
Good as an intermediate file location in sequences of jobs
DataStage官方培训教程7
This document and the software described herein are the property of Ascential Software Corporation and its licensors and contain confidential trade secrets. All rights to this publication are reserved. No part of this document may be reproduced, transmitted, transcribed, stored in a retrieval system or translated into any language, in any form or by any means, without prior permission from Ascential Software Corporation.
Copyright © 2003 Ascential Software Corporation. All rights Reserved
Ascential Software Corporation reserves the right to make changes to this document and the software described herein at any time and without notice. No warranty is expressed or implied other than any contained in the terms and conditions of sale.
easy retrieval
Types of Hashed Files
21 different types Type 1 and 19 do not use a hashing algorithm Types 2-18 are static hashed files and use a
hashing algorithm Type 25 is static and uses a B-tree algorithm Type 30 is dynamic and uses a hashing algorithm
Main use is as a reference lookup table
Hashing Algorithms (Static File Types)
Character type
Location where most variation occurs in key column
Right
Middle
Left
Any
Wholly numeric
2
6
10
14
Numeric & separators
3
ASCII
4
Any
5
7
11
15
8
Fra Baidu bibliotek
12
16
9
13
17
Inserting Records into Hashed Files
Hashing Algorithm
Group 1 Group 2 Group 3 Group 4 Group 5
Overflow Groups
When there is not enough space remaining in a group, the group overflows