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Updates to IBM Tools Base for z/OS V1.6 IMS Hardware Data Compression Extended User's Guide and Reference (SC19-4373-02)

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Abstract

Updates to IBM Tools Base for z/OS V1.6 IMS Hardware Data Compression Extended User's Guide and Reference (SC19-4373-02)

Content

The most recent updates appear at the top of the list.


Update 2

Date of change: May 2020

Change description: User's guide updates. 

Topics: Changes apply to multiple topics.

------------------------------

Topic: Building and relinking a dictionary > Modifying a DBD

This topic has been updated as follows:

Procedure

1. Add or change the COMPRTN keyword of the SEGM statement for each segment that contains compressed data. The COMPRTN keyword must specify either KEY or DATA compression, and must specify INIT. For more information, see "COMPRTN keyword".

The following example shows how to enter the COMPRTN keyword of the SEGM statement for fixed-length segments:

SEGM NAME=SEGMENTA,PARENT=0,BYTES=256,PTR=TB,
     COMPRTN=(DRVRSCNM,DATA,INIT)

The following example shows how to enter the COMPRTN keyword of the SEGM statement for variable-length segments:

SEGM  NAME=SEGMENTA,PARENT=0,BYTES=(256,16),PTR=TB,
      COMPRTN=(DRVRSCNM,DATA,INIT) 
2. Modify the COMPRTN or the BYTES parameter to allow for 10 byte control information.
If the format or contents of the data in a segment precludes compression, the HDCE exit routine adds control information that indicates that the segment cannot be compressed.
The control information might lengthen the segment beyond the maximum length definition. For example, an application on a test IMS system uses a production compression exit. If the test application tries to insert an X'00' string segment and no X'00' data was present when the production dictionary was built, then that input string cannot be compressed.
Failure to increase the MAXBYTES field by 10 might result in an ABENDU0853.  Follow these instructions to allow for 10 byte control information:
  • Fixed-length segment: Omit the PAD parameter, and omit the max parameter or specify 10 (default) for the max parameter of the COMPRTN keyword of the SEGM statement. If you want to use the PAD parameter to control segment padding, see "Step 3".
  • Variable-length segment: Increase the max bytes parameter of the BYTES keyword of the SEGM statement by 10 from the maximum length before compression.
  • DEDB: If your database is a DEDB, make sure that the new MAXBYTES field is at least 120 bytes less than the VSAM control interval (CI) size. If it is not, you must redefine your VSAM CI size.
  • Segments that cannot be compressed due to data inconsistency: If a segment cannot be compressed due to data inconsistency, IMS manages the increased length internally with no affect to the application or DBD. For more information, see the topic "Database Manager exit routines" in IMS Exit routines.

3. Optional: If you want to control segment padding, adjust the parameters.
If the compressed segment is frequently replaced by applications, consider adjusting the padding length. When a segment is replaced and the new data length after compression becomes longer, it could cause data fragmentation, which affects database performance. By specifying appropriate padding, IMS adds padding space to the value for the segments that are heavily compressed and reduces fragmentation.
  • Fixed-length segment: Specify the padding length with the max parameter and the PAD parameter of the COMPRTN keyword of the SEGM statement. The max parameter, when specified with the PAD parameter, is treated as the padding length. In this case, the default length, which is 10 bytes, is added for control information.
    SEGM NAME=SEGMENTA,PARENT=0,BYTES=256,PTR=TB,
         COMPRTN=(DRVRSCNM,DATA,INIT,150,PAD)
    

    Padding length and the PAD parameter are not supported for DEDBs.

  • Variable-length segment: Specify the padding length with the min bytes parameter of the BYTES keyword of the SEGM statement.
    SEGM NAME=SEGMENTA,PARENT=0,BYTES=(266,150),PTR=TB,
         COMPRTN=(DRVRSCNM,DATA,INIT) 
    
To determine the padding value for each segment, review the Segment Distribution by Compressed Length report (HCO007). For details, see "Segment Distribution by Compressed Length report (HCO007)".
4. Run an ACBGEN for online databases. Running ACBGEN is required whenever you modify a DBD.
------------------------------
Topic: Building and relinking a dictionary > COMPRTN keyword

This topic has been updated as follows:

The COMPRTN keyword of the SEGM statement for each segment that contains data must be modified to allow for data compression.

Purpose

The COMPRTN keyword statement specifies the compression exit routine.

>>--COMPRTN=--(EXITNAME-+-,DATA-+-+-------+-+---------------+-)---><  
                        '-,KEY--' '-,INIT-' '-,max-+------+-'       
                                                   '-,PAD-'

Parameters
The following parameters apply to both variable-length and fixed-length segments:
EXITNAME
...
INIT
...
The following parameters apply to fixed-length segments:
MAX max
When specified without the PAD keyword, the max value specifies the maximum number of bytes by which fixed-length segments can increase during compression exits. You can specify from 1 bytes to 32,767 bytes. This keyword is optional. If omitted, the default value 10 is used.
When specified with the PAD keyword, the max value specifies the padding length. For more information, see the description of the PAD keyword.
PAD
Use the PAD keyword to indicate that the numeric value that is supplied in the previous parameter of max is used for padding. The numeric range from 1 to 32767 still applies; however, it is used in a different way. The value specifies a size to which an inserted segment is padded when the compression of that segment results in a length less than the PAD value. This keyword is optional.
The following example shows how to enter the COMPRTN keyword of the SEGM statement for fixed-length segments:
SEGM  NAME=SEGMENTA,PARENT=0,BYTES=256,PTR=TB,
      COMPRTN=(DRVRSCNM,DATA,INIT,150,PAD)
The following example shows how to enter the COMPRTN keyword of the SEGM statement for variable-length segments:
SEGM  NAME=SEGMENTA,PARENT=0,BYTES=(266,150),PTR=TB,
      COMPRTN=(DRVRSCNM,DATA,INIT)
------------------------------
Topic: Extracting data > Image Copy Extract utilities > Image Copy Extract JCL requirements

The names of sample JCL members have been updated as follows:

 

Table. JCL members for accessing the Image Copy Extract utilities

(Table 5 in PDF)

Function Sample JCL member
Detail Analyze HCOJOB1A
Analyze HCOJOB2A
Build HCOJOB3A
Examine HCOJOB4A
------------------------------

Topic: IMS HD Compression Extended overview

This topic has been updated as follows:

IMS HD Compression Extended provides functions for compressing IMS data. IMS HD Compression Extended uses the z/OS hardware data compression (HDC) that is available on IBM processors.
IMS provides a basic utility that supports z/OS HDC. IMS HD Compression Extended provides enhanced functions that supports z/OS HDC that are not available in the basic IMS utility. IMS HD Compression Extended can be used to compress HDAM, HIDAM, PHDAM, PHIDAM, HISAM, and Fast Path databases.
------------------------------
Topic: IMS HD Compression Extended overview > IMS HD Compression Extended features and benefits
This topic has been updated as follows:
IMS HD Compression Extended and other IMS Tools
Many IMS tools provide database management features that are not available in IMS itself or provide enhancements to capabilities built into IMS.
IMS HD Compression Extended is only one of several IMS tools that provide enhancements to the process of database administration and change management.
Other IMS Tools products that can assist with database administration and change management include:
  • IMS Database Solution Pack
  • IMS Database Utility Solution
  • IMS Fast Path Solution Pack
  • IMS Recovery Solution Pack
  • IMS Transaction Manager Solution Pack
  • IMS Sequential Randomizer Generator
IMS HD Compression Extended is a vital part of managing your IMS database system.
------------------------------

Topic: Configuring IMS HD Compression Extended

Link to the IBM Tools Base for z/OS Configuration Guide has been corrected:

Information about configuring IMS HD Compression Extended and other Tools Base components for IMS is provided in IBM Tools Base V1.6 Configuration Guide.

Update 1
Date of change:
August 2018
Change description: Typographical edit for HDCDSTAT pathname.
Topics: (Chapter 8.) Examining an existing dictionary > Examine JCL requirements

The pathname for HDCDSTAT erroneously contains a "comma" instead of a "period".

The pathname with the correct punctuation is indicated below:

HDCDSTAT
The name of the custom dictionary statistics data set (hlq.dictname.HDCDSTAT).

Publication Number

SC19-4373-02

Original Publication Date

01 October 2016

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Document Information

Modified date:
26 May 2020

UID

ibm10720097