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USING EXCP TO WRITE AN EOF MARK TO A BSAM DATASET

IP.com Disclosure Number: IPCOM000014323D
Original Publication Date: 2001-Feb-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Abstract

In IMS 410, users browse the spool data set via Time Sharing Option(TSO) as it is being written to by IMS. This support consists of writing an end of file (EOF) mark after each message is written to delineate the end of the current data. The EOF marks are overwritten by each write of a new record. The spool data sets are written to using the BSAM access method and the EOF marks are written by issuing a 'Close Type=T' (TCLOSE) macro. This support is especially useful to customer system programmers when the secondary master terminal (MTO) is assigned to a spool line. They can browse the active MTO spool data set to view MTO messages and analyze problems. This support has caused performance degradation in some cases because of the overhead of the 'Close Type=T'. Issuance of a 'Close Type=T' results in extra writes to the Volume Table of Contents(VTOC) to update the Format-1 Data Set Control Block(F1 DSCB), causing up to 4 I/O's to complete

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USING EXCP TO WRITE AN EOF MARK TO A BSAM DATASET

   In IMS 410, users browse the spool data set via Time Sharing Option(TSO) as it is being written to by IMS. This support consists of writing an end of file (EOF) mark after each message is written to delineate the end of the current data. The EOF marks are overwritten by each write of a new record.

The spool data sets are written to using the BSAM access method and the EOF marks are written by issuing a 'Close Type=T' (TCLOSE) macro.

This support is especially useful to customer system programmers when the secondary master terminal (MTO) is assigned to a spool line. They can browse the active MTO spool data set to view MTO messages and analyze problems.

This support has caused performance degradation in some cases because of the overhead of the 'Close Type=T'. Issuance of a 'Close Type=T' results in extra writes to the Volume Table of Contents(VTOC) to update the Format-1 Data Set Control Block(F1 DSCB), causing up to 4 I/O's to complete
writing a single record.

To improve performance of the EOF writes, the following change to IMS spooled dataset support is proposed:

When the data set is opened and the first record is written, an Execute Channel Program(EXCP) call is issued to write a EOF mark on the second track.

As each new record is written on the track, a NOTE is issued to determine when the end of track was reached and the EOF mark was overwritten.

When the EOF mark is overwritten, another EXCP is issued to write a EOF on the next track. On the last track of the data set no EOF is written because BSAM can detect the end of data set and simulate a EOF condition.

This operation reduces the EOF writes from one per record to one per trac...