DB2 for z/OS and List Prefetch Optimizer

An IBM Redpaper publication

Published 26 July 2012, updated 19 February 2013

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IBM Form #: REDP-4862-00
(22 pages)

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Authors: Jeff Berger, Paolo Bruni


The tight integration that IBM® DB2® for z/OS® has with the IBM System z® architecture and the z/OS environment creates a synergy that allows DB2 to use advanced z/OS platform functions. This synergy includes the enterprise storage systems.

DB2 10 for z/OS, available from October 2010, has improved its sequential detection algorithm by introducing the row level sequential detection function. This function helps reduce synchronous I/Os when doing a range scan, and the cluster ratio is less than 100%. DB2 10 for z/OS also introduced the use of list prefetch for disorganized index scans.
The IBM System Storage® DS8000® Licensed Machine Code (LMC) level R6.2, available from November 2011, delivered several performance enhancements. When using R6.2, all DB2 I/Os, including format writes and list prefetches, are eligible for IBM High Performance FICON® (zHPF). In addition, DB2 can benefit from the new caching algorithm at the DS8000 level called List Prefetch Optimizer that the R6.2 introduced. In June 2012, the DS8000 R6.3 increased the capacity of SSD storage to 400 GB, introduced SSD full disk encryption, and further improvements to List Prefetch Optimizer.

In this IBM Redpaper™ publication, we show DB2 10 for z/OS performance measurements on zEC12 processor using DS8000 R6.2 and R6.3 with DS8800 and solid-state drives. The measurements highlight both the reduction gained in synchronous I/O and the reduced dependency on data reorganization. This combination offers the opportunity for better performance to critical SQL applications that access large fragments of disorganized data.

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