ELIB performance.

Document ID : KB000011286
Last Modified Date : 14/02/2018
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Introduction:

ELIB performance is not only dependent of the number of file extents, but may also be impacted by the number of directory overflows.

Question:

How can you optimize the performance when using ELIB?

Answer:

Usually the performance of BDAM and VSAM ELIB files is very good compared to PDS or PDS/E but to obtain optimal ELIB performance a few rules must be observed. We recommend on that the following be completed on a monthly basis:

  • Ensure that the ELIB file does not contain more than 1 physical extent.

    ==> for VSAM ELIBs, run IDCAMS LISTCAT ENT(elib.dsname) ALL and check the number of extents. If the file has more than one extent, define larger file and use IDCAMS repro to copy the data.

  • Ensure that the ELIB directory overflow count is zero or close to zero.

    ==> run BC1PNLIB INQUIRE and check the output line containing the number of DIRECTORY OVERFLOWS. If its number is not zero a BC1PNLIB REORG job should be run to reorganize the ELIB directory pages. In this case, we recommend to increase the number of directory pages by ten percent.

All Endevor utilities that do many ELIB reads, like UNLOAD, SEARCH/REPLACE, BC1PNCPY will benefit greatly of single extent files with a well organized directory. Individual Endevor actions will also benefit of well organized files, but the difference will be hard to measure for each action.
In one reported case the elapsed time of a full unload got reduced from 8 hours to 25 minutes (merely five percent of the original elapsed time) after reorganizing the directory of the base and delta files. The ELIB reorganization took less than 2 minutes.

Below is an illustration that shows how a Generate action against 2398 elements has its elapse time strongly reduced after a Directory Reorganization:

After a lot of activities (The directory was strongly unorganized), running a BC1PNLIB INQUIRE shows that both BASE and DELTA libraries have # DIR OVERFLOWS: 49.

Remarks : The Directory overflow number can be less than '10' which is a small number of overflows, but each block of directory page can be very disorganized.

Before Reorganizing the Directory, the Elapse time spent to perform a generate action of 2398 elements was 00:13:55.14
After Reorganizing the Directory, the Elapse time spent to perform a generate action of 2398 elements is 00:05:41.58

The elapsed time of generate got reduced from 13 minutes 55 seconds to 5 minutes 41 seconds (41 percent of the original elapsed time) after reorganizing the directory of the base and delta files.

Result of BC1PNLIB/Inquire before REORG :

ENDEVOR-LIB INQUIRY: DDNAME=ELIBVSAM                              
         DDNAME:                   ELIBVSAM                       
         DSNAME:                   PUBLIC.JELB1203.STG1.VSAM      
         LIBRARY TYPE:             VLB                            
.../...        
         LAST UPDATE:              12/09/2009   04:01:59.51
         LATEST MEMBER:              NDVR LIB              
         AVG PAGES/MEMBER:                 1               
         # DATA PAGES:                  2398               
         # REPLACES:                       0               
         # ADDS:                        2398               
         # DELETES:                        0               
         # MEMBERS:                     2398               
         # DIRECTORY PAGES:               99               
         # DIR OVERFLOWS:                 49               
         LONGEST DIR OVFL:                 1               
         # LIBRARY EXTENDS:                1               
         # DIRECTORY REORG:                1 

In order to reorganize the ELIB in the most accurate way, you need to know the number of used Directory pages, this number can be found in the BC1PNLIB/INQUIRE, the sample SYSOUT shows : # DIRECTORY PAGES: 99
The value coded to Reorganize the Directory is 110.
The SYSIN used to reorganize Directory with BC1PNLIB is : REORG DDNAME=ddname DIRECTORY PAGES = 110.

Here is a sample JCL :

//*********************************************************************
//* REORG DIRECTORY A VSAM BASE LIBRARY AT STG1                        
//*********************************************************************
//REORBAS3  EXEC PGM=NDVRC1,PARM=BC1PNLIB                                         
//STEPLIB  DD DISP=SHR,DSN=uprfx.uqual.AUTHLIB
//         DD DISP=SHR,DSN=iprfx.iqual.CONLIB                     
//ELIBVSAM DD DISP=OLD,DSN=elib.dsname                
//SYSPRINT DD SYSOUT=*                                                
//BSTERR   DD SYSOUT=*                                                
//SYSIN    DD *                                                       
 REORG DDNAME=ELIBVSAM DIRECTORY PAGES = 110.                            
 INQUIRE DDNAME = ELIBVSAM                                              
 .                                                                    
/*

Result of BC1PNLIB/Inquire after REORG :

ENDEVOR-LIB INQUIRY: DDNAME=ELIBVSAM                              
         DDNAME:                   ELIBVSAM                       
         DSNAME:                   PUBLIC.JELB1203.STG1.VSAM      
         LIBRARY TYPE:             VLB                            
.../... 
        LAST UPDATE STAMP:             2465               
        LAST UPDATE:              12/09/2009   04:16:05.11
        LATEST MEMBER:              NDVR LIB              
        AVG PAGES/MEMBER:                 1               
        # DATA PAGES:                  2398               
        # REPLACES:                       0               
        # ADDS:                        2398               
        # DELETES:                        0               
        # MEMBERS:                     2398               
        # DIRECTORY PAGES:              110               
        # DIR OVERFLOWS:                  0               
        LONGEST DIR OVFL:                 0               
        # LIBRARY EXTENDS:                1               
        # DIRECTORY REORG:                2 

For more information about the utilities mentioned above, please refer to the CA Software Change Manager for Mainframe - Utilities Guide chapter 2, BC1PNLIB INQUIRE and BC1PNLIB REORG.

Additional Information:

If you have any questions or concerns please do not hesitate to contact your local CA Endevor Support Team.

For more information on ELIBS please see:

CA Endevor Administrating Guide - Chapter - ELIB Data Sets.

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