Change listing library Endevor compression to zEDC compression
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Change listing library Endevor compression to zEDC compression


Article ID: 245848


Updated On:




The listing library datasets (from compile output) are compressed.
Compression of PDSEs can now be done by zEnterprise Data Compression (zEDC) - is it possible to use this instead? Has any evaluation of this been done as an alternative?


Release : 18.0 18.1 

Component : Endevor Software Change Manager


In this case the listing libraries were PDSE datasets with RECFM=VBA which means they are compressed because the CONLIST Utility compresses a VBA dataset by default.

Endevor Engineering provided the following advice:
zEDC compression at the data set level is transparent to the Endevor application and can be activated any time. Compressing data that's already in some compressed format usually doesn't provide a significant benefit.
There would be 2 ways to test the compression differences:
1. Comparison without making any changes to Endevor i.e. copy the contents of the current listing library to a zEDC-compressed one and compare the space used.
2. Comparison of Endevor compression to zEDC compression i.e. convert the Endevor listing library to one on which zEDC compression is active and which has fixed length (Record Format=FBA) so it is not compressed by Endevor.
The expectation is that the second approach will be the more CPU efficient because software compression is replaced with hardware compression. There is no prediction about which compression will be most DASD-efficient.

Test #2 was run by user using BC1PNCPY Utility to copy/uncompress the existing Endevor VBA listing library dataset to a zEDC compressed FBA listing library dataset i.e. COPY INPUT FILE (VBA) to OUTPUT FILE (FBA) with the UNPACKED option set only on the OUTPUT.
The size of the resulting zEDC compressed FBA listing library (Used pages = 394,147) represented a gain of 66% in free space compared to the original Endevor compressed VBA listing library (Used pages = 1,130,893)

Endevor Engineering also tested as follows on a z15 LPAR with integrated compression.
For a listing library with 1182 members:
a. Without any compression, 407611 pages are used
b. With Endevor compression, 76173 pages (gain: 81%)
c. With zEDC-compression of Endevor-compressed data, 63033 pages (gain: 84%)
d. With zEDC-compression of uncompressed Endevor data, 57602 (gain: 86%)
As for the impact on CPU, that depends on how much Endevor compression/decompression takes place. For "normal" Endevor work like generating and moving elements, the impact is small. However, for work that involves reading or writing all members of a library (e.g. BC1PNCPY), the impact is high. Having said that, the latter work only happens occasionally or even almost never. Note that UNLOAD copies PDSE members "as is", i.e. there's no compression/decompression being done.

Additional Information

1. Example JCL for BC1PNCPY:
//STEPLIB  DD DISP=SHR,DSN=hlq.mlq.CSIQAUTU              
//         DD DISP=SHR,DSN=hlq.mlq.CSIQAUTH              
//CONLIB   DD DISP=SHR,DSN=hlq.mlq.CSIQLOAD              
//ELIBI    DD DISP=SHR,DSN=hlq.mlq.ELIB                  
//ELIBO    DD DISP=SHR,DSN=hlq.mlq.PDSE                  
//SYSIN    DD *                                          
     INPUT  DDN ELIBI                                    
     OUTPUT DDN ELIBO                                    
     MEMBER *                                            
//BSTERR   DD SYSOUT=*                                    
//SYSPRINT DD SYSOUT=*                                    
//SYMDUMP  DD DUMMY                                      

2. IBM zEDC Compression information for PDSEs: Creating Compressed Format PDSEs
NOTE: zEDC compression is not performed for members smaller than 64KB.