Cruising with Multiple Reference Check

Tom Brocker, IBM TPF ID Core Team, and Rob Dunn, IBM TPFDF Development

TPFDF CRUISE (capture/restore utility, information and statistics environment) gets a performance tune-up with APAR PQ36341 that can improve the way you manage your system resources. TPFDF PUT 14 introduces multiple reference check (MRC) support, which is a method that modifies CRUISE capture processing so that detailed files referenced from more than one index file are chain chased only once.

With MRC support, redundant chain chasing is eliminated because each subfile is captured once and only unique data is saved to tape. This reduces the amount of tape required while improving CPU and I/O processing time.

Without MRC support, CRUISE processing chain chases every detail file referenced in the same prime block. This results in additional chain chasing time, an increase of data captured to tape, and a decrease in the performance of your TPF 4.1 system or ALCS environment.

To benefit from MRC support, specify the optional MRC parameter with the CAPTURE parameter of the ZFCRU SETUP command. To get an idea of how MRC processing works, lets take a peek under the hood of CRUISE processing.

The following example shows a data structure with intermediate detail file CCCC referenced from both top-level index files AAAA and BBBB; detail files DDDD and EEEE are referenced from CCCC.

The following example shows a sequence of blocks written to tape using CRUISE capture processing without MRC support specified for prime blocks AAAA and BBBB. In this example, six blocks (three control and three data blocks) are written twice to tape. In addition, take into account the time for chain chasing blocks CCCC, DDDD, and EEEE again, and the time required to build the control blocks.

Note: Subfiles are captured to tape as data blocks; for each data block written to tape, a control block is also written. The control block contains a high-level reference of the data block; for example, file address, partition or interleave number, ordinal number, and prime or chain indicator.

The following example shows redundant chain chasing eliminated by using CRUISE capture processing with MRC support specified for prime blocks AAAA and BBBB.

MRC support is particularly beneficial if your database contains a large amount of data with subfiles referenced by index files. However, using MRC support can result in inaccurate results when you specify the STATISTICS parameter with the ZFCRU SETUP command. Additionally, the ADR and WID parameters of the ZFCRU SETUP command are not supported with CRUISE restore processing when the database is captured using MRC support. See TPFDF Utilities for more information about MRC support.

The #IRCMDF fixed file record defines the number of ordinals when using CRUISE with MRC support. See TPFDF Installation and Customization for more information about the #IRCMDF interface record and the formula to calculate the number of ordinals.

Third Quarter 2000 - Table of Contents