Selecting the scan method

IMS Index Builder provides a sequential scan technology for building primary, secondary, and ILDS indexes, and this sequential scan technology is used as the default scan method. However, you can change the scan method to apply the scan method that was used in IMS Index Builder 2.3.

About this task

When you build a primary index and secondary indexes together in IMS Index Builder 2.3, the primary database was scanned twice, once by using the sequential scan method and once by using the hierarchical HPU scan method. However, in this version of IMS Index Builder, the primary database is scanned only once by using the sequential scan method, which reduces the elapsed time.

When the sequential scan method is used to build one or more secondary indexes, several sort tasks are started depending on the segment level of the index sources. The segment occurrences of the primary database are read in physical order, then the index pointers and the index keys are collected and sorted in hierarchical order. For example, when segment level of an index source is the second level of dependent segments, two sort tasks (IIUSRTV1 and IIUSRTV2) are started, and when the index target or the index source is a variable-length segment, an additional sort task (IIUSRTD0) is started.

The messages from the sort tasks are printed in the IIUSOUT data set. The following figure shows an example of the sort messages.
Figure 1. Sort messages in the IIUSOUT data set
        IIUSRTV1 PPP9PPP1 SEQSCAN SORT MESSAGES:            DURATION                                         
        ----------------------------------------------------------84--                                       
ICE200I 0 IDENTIFIER FROM CALLING PROGRAM IS CA12                                                            
ICE201I A RECORD TYPE IS F - DATA STARTS IN POSITION 1                                                       
ICE751I 0 C5-I40658 C6-I35397 C7-I35397 C8-I40658 E4-I40658 C9-I35397 E5-I38877 E6-I31999 C4-I31999 E7-I40658
ICE143I 0 BLOCKSET     SORT  TECHNIQUE SELECTED                                                              
ICE250I 0 VISIT http://www.ibm.com/storage/dfsort FOR DFSORT PAPERS, EXAMPLES AND MORE                       
ICE000I 0 - CONTROL STATEMENTS FOR 5650-ZOS, Z/OS DFSORT V2R3  - 08:03 ON TUE OCT 05, 2021 -                 
          SORT FIELDS=(001,010,CH,A),DYNALLOC,FILSZ=E000001000000                                            
          RECORD TYPE=F,LENGTH=00195                                                                         
          OPTION MSGDDN=IIUSRTV1,SORTDD=T009                                                                 
          DEBUG ABEND                                                                                        
ICE193I 0 ICEAM2 INVOCATION ENVIRONMENT IN EFFECT - ICEAM2 ENVIRONMENT SELECTED                              
:

These sort tasks require additional sort workspace. The sort file size of IIUSRTVx is estimated based on the sum of index records, and the estimated value is given to the SORT FILSZ option. When the VSAM data set for the index is not reused, the number of index records is estimated based on the allocation characteristics of the VSAM data set. You can override the estimated value by using the SORTFSZ control statement.

When additional sort workspace is not available, you can use the scan method that was used in IMS Index Builder 2.3.

Procedure

Specify the MAXTASKS 2 control statement. The MAXTASKS 2 control statement specifies IMS Index Builder to use the hierarchical HPU scan method for building secondary indexes, such as in IMS Index Builder 2.3. When the MAXTASKS 2 control statement is specified, additional sort workspace is not needed.
When the IMS Index Builder job ends, you can identify the scan method that was used in the event log that is printed in the IIUSNAP data set. The following figure shows an example of the event log.
Figure 2. Event log in the IIUSNAP data set
IIUE096M A0000777 008C0BF8 IB CONTROL FLOW EVENT 603 AT IIUSCA01 12.00.00.00
                SEQUENTIAL SERIAL SCANNER ACTIVATED                        

IIUE096M A0000777 006D5D08 IB CONTROL FLOW EVENT 609 AT IIUSCA12 12.00.00.00 
                 SEQUENTIAL SAS SCANNER ACTIVATED                            

IIUE096M A0000777 007A1088 IB CONTROL FLOW EVENT 623 AT IIUSCA55 12.00.00.00
                HIERARCHICAL HPU SCANNER ACTIVATED