Improving availability of a restartable staged storage data base system that uses logging facilities

• US 4,751,702 A
• Filed: 02/10/1986
• Issued: 06/14/1988
• Est. Priority Date: 02/10/1986
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Watts, Vern L., Beier, Harley A., Fukumoto, Takeshi, Scofield, Harrison
• Primary Examiner(s): ATKINSON, CHARLES
• Application Number:
  US06/828,113
• Time in Patent Office: 855 Days
• Field of Search: 371/9, 371/12, 364/187, 364/200, 364/900
• US Class Current: 714/13
• CPC Class Codes: G06F 11/203 using migration
• CPC Class Codes: G06F 11/2038 with a single idle spare processing component
• CPC Class Codes: G06F 11/2046 where the redundant components share persistent storage G06F11/2043 takes precedence
• CPC Class Codes: G06F 11/2097 maintaining the standby controller/processing unit updated initialisation or re-synchronisation thereof G06F11/1658 and subgroups
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A method is disclosed for maintaining availability of a restartable data base system where continuity of service is guaranteed by having a loosely-coupled backup processor taking over processing of a degraded active processor. The backup processor continuously tracks the activities of the active processor to ascertain data set elements updatable by the active processor. Upon switchover, images of data set elements updatable by the degraded active processor are created in the buffer of the backup processor. By making references and updates to the images, processing of the backup processor can start immediately after switchover. Upon preventing the degraded active processor from making further updates, the backup processor writes the images back to the data base.

Claims

1. A method for maintaining data availability in a data base system having backup and active processors, said system utilizing staged storage and logging facilities, comprising the steps by a backup processor of:

(a) ascertaining the names and locations of the data set elements in staged storage which are updatable by the active processor, and upon the passing of control from a degraded active processor to the backup processor, logging the ascertained names and locations;

(b) ascertaining whether the degraded active processor ceases to perform updates to staged storage;

(c)upon the first reference to each data set element in staged storage by said backup processor, copying said referenced element to a buffer, diverting subsequent references from staged storage to the buffer copy, logging each update to said copy, the steps of copying, diverting, and logging being repeated until indication of said degraded active processor ceases to perform updates to staged storage; and

(d) writing the buffer contents back to staged storage.

2. A method for maintaining data availability in a restartable data base system, said system utilizing staged storage and logging facilities, said data availability being extended to those data sets having associated therewith access errors, comprising the steps of:

(a) responsive to each access error, creating a concordance of the affected data set name, location, and error type, copying said affected data to another staged storage location, and logging the concordance and a copy of the affected data to staged storage;

said logging also being invoked at periodic checkpoints;

(b) diverting subsequent references from staged storage to the buffer copy, logging each update to said copy, the steps of copying, diverting, and logging being repeated until said access error becomes resolved;

(c) in the event of system restart, restoring the concordance and the affected data from the log to staged storage; and

(d) restoring said error by successfully writing the buffer contents back to staged storage.