z/OS V1R6.0 DFSMS Access Method Services for Catalogs

DEFINE ALTERNATEINDEXTo ensure data integrity in a shared environment, VSAM provides users ofSHAREOPTIONS 4 (cross-region and cross-system) with the followingassistance:vvEach PUT writes the appropriate buffer immediately into the VSAMobject’s DASD. VSAM writes out the buffer in the user’s address spacethat contains the new or updated data record.Each GET refreshes the user’s input buffers. The contents of each dataand index buffer used by the user’s program is retrieved from theVSAM object’s DASD.Exception: If you use VSAM RLS or DFSMStvs, SHAREOPTIONS is assumedto be (3,3). If you do not use VSAM RLS or DFSMStvs, the SHAREOPTIONSspecification is respected.Abbreviation: SHRSPEED|RECOVERYSpecifies whether the data component’s control areas are to be preformattedduring loading.This parameter is only considered during the actual loading (creation) of a dataset. Creation occurs when the data set is opened and the high-used RBA isequal to zero. After normal CLOSE processing at the completion of the loadoperation, the physical structure of the data set and the content of the data setextents are exactly the same, regardless of which option is used. Anyprocessing of the data set after the successful load operation is the same, andthe specification of this parameter is not considered.If you use RECOVERY, the initial load takes longer because the control areasare first written with either empty or software end-of-file control intervals.These preformatted control intervals are then updated, using update writeswith the data records. When SPEED is used, the initial load is faster.SPEEDDoes not preformat the data component’s space.If the initial load is unsuccessful, you must load the data set again fromthe beginning because VSAM cannot determine the location of your lastcorrectly written record. VSAM cannot find a valid end-of-file indicatorwhen it searches your data records.RECOVERYDoes preformat the data component’s space prior to writing the datarecords.If the initial load is unsuccessful, VSAM can determine the location of thelast record written during the load process.Abbreviation: RCVYTO(date)|FOR(days)The retention period for the alternate index. The alternate index is notautomatically deleted when the expiration date is reached. When you donot provide a retention period, the alternate index can be deleted at anytime. The MANAGEMENTCLASS maximum retention period, if used,limits the retention period named by this parameter.For non-SMS-managed data sets, the correct retention period is reflected inthe catalog entry. The VTOC entry might not have the correct retentionperiod. Enter a LISTCAT command to see the correct expiration date.Chapter 13. DEFINE ALTERNATEINDEX 139