An overview of CA Datacom Forward and Backward Recovery processing

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Article ID: 18722

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Products

CA Datacom CA Datacom/DB CA Datacom/AD

Issue/Introduction

As application programs run, the expectation is that these programs will process the data correctly, and the devices on which the files are stored will also work correctly. Unfortunately, not all programs are perfect, and not all disk devices work correctly forever. This means that a database might at some point need to be processed to either back out some erroneous updates, or a database might need to be rebuilt from a backup point forward to a device failure.

This is a process known as Backward Recovery (to roll back some updates) or Forward Recovery (to recover forward from a fixed starting point.). In order to accomplish this, you will recover the problem databases using the RXX records produced from a DBUTLTY SPILL of the log file (LXX) to a recovery file (RXX). This document will cover some of the primary points and questions that users have when using this utility.

Environment

Component : CA Datacom/DB

Component : CA Datacom/AD

Resolution

The first thing needed to run this utility is a list of the RXX files to process. The RXX file allocation (with z/OS DD or z/VSE DLBL statements) must start with the oldest file, and concatenate subsequent RXX files in order through the latest or most recent RXX file. This convention is used for both Forward and Backward Recovery.

Next, we need to identify the date/time range of the records to process if using forward recovery. This is always of the format from.date.time/to.date.time. Typically, Backward Recovery will be used to reverse changes for a particular TSN (Transaction Sequence Number), or possibly for a job, so the time range is not necessarily needed here. 

At this point, we have identified the RXX input source in order from oldest to latest, and we have determined the range of RXX records to process, from oldest to latest. Now, we can either do a Forward or Backward recovery - internally, we start at the oldest.date.time and bring the updates forward for Forward Recovery, and for Backward Recovery we start at the latest.date.time (or end of the file) and process backwards.

There are a couple assumptions about this process:

  1. For Forward Recovery, we assume that the starting point is a backup file that was reloaded, and the oldest.date.time will be the same as that backup date/time. The utility will check that the oldest RXX record to process will match the state of the record using the oldest "Before" image.
  2. For Backward Recovery, we assume that the starting point is the current file state, and that we have all the log records available in the set of RXX files to roll back to the oldest.date.time. The utility will look at the latest "After" record in the RXX, and expect the current record in the database will match it.

There are many other options, settings and selection criteria that can be specified to provide a great amount of flexibility and power to update your databases as you desire.

Additional Information

For more information about these settings and about the process, please refer to the CA Datacom/DB Database and System Administration documentation section called "Using Recovery" and the DBUTLTY Reference section called "RECOVERY Command (RECOVERY)."

As always, please contact Broadcom support for CA Datacom if you have further questions.