US 5,280,611 AGranted

Method for managing database recovery from failure of a shared store in a system including a plurality of transaction-based systems of the write-ahead logging type

AssigneeInternational Business Machines Corporation

InventorsChandrasekaran Mohan, Inderpal S. Narang, James Z. Teng

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Abstract

In a multi-system data sharing complex, a database system can write updated pages to a shared electronic store for a fast write. Other database systems can obtain pages written to the shared store for further modification without the pages first being written to stable storage. However, pages are eventually written to the stable storage in a castout process. Recovery of a database from failure of the shared store is bounded by determination of a recovery boundary which, when applied to the union of database system transaction logs, establishes a point in front of which are found log records of modifications to pages which were in the shared store when it failed. These log records are applied to page versions obtained from stable storage to recover from failure of the shared store.

Claims11

Dependent claims

In a multi-computer datasharing system including a shared electronic store (SS), a low-speed direct access data storage facility (DAS), a plurality of independently-executing database systems connected to the SS and to the DAS, and a database including data in the DAS, wherein each database system includes:

transaction-based means for obtaining data structures from the DAS, modifying the data structures locally and placing the data structures in the SS for access by other database systems;
a log and transaction means for entering into the log a sequence of records corresponding to modifications made to data structures;
and
log records from different database systems can be sequenced;
a machine-executable method for maintaining a transaction log boundary for recovery of the database from failure of the SS, the method including the steps of:
for each database system, ascertaining a system sequence value which is substantially equivalent to the log sequence location of a log record recording the earliest modification to a data structure at the database system which is not included in any data structure in the SS;
at each database system, for each data structure modified at the database system, providing a sequence value which is less or equal to a log sequence location of the log record recording the earliest modification to the data structure;
for each data structure in the SS, based upon sequence values provided by the database systems, ascertaining a structure sequence value corresponding to a log sequence location of a log record of the earliest modification of the data structure occurring after the data structure was obtained from the DAS;
and
ascertaining from the system and data structure sequence values a recovery boundary corresponding to the earliest of the system and structure values.

7 more elements

In a multi-computer data sharing system including a shared, high-speed electronic store (SS), a low-speed direct access data storage facility (DAS), a plurality of computer-implemented database systems connected to the SS and to the DAS, and a database including data structures stored in the DAS, wherein each database system includes transaction-based means for:

obtaining data structures from the DAS;
locally storing data structures for immediate access;
altering locally-stored data structures;
and
storing data structures in and from and moving data structures from the SS;
a method for recovery of the database from failure of the SS, the method including the steps of:
maintaining for each database system a transaction log including a sequence of log records, each log record including a unique sequence value denoting its place in the sequence;
maintaining at each database system a system sequence value which is substantially equal to the sequence value of a log record of the earliest modification made by the database system to locally-stored data structures which is not included in any data structure stored in the SS;
maintaining for each data structure modified and then stored in the SS a structure sequence value which corresponds to a log record of the earliest modification made to the data structure by a database system after the data structure was obtained from the DAS;
periodically determining a recovery sequence value by taking from the system sequence values and the structure sequence values a sequence value which corresponds to a log record of the earliest modification made to any data structure which is locally stored at a database system or in the SS;
and
in the event of a failure of the SS:
for the union of all the transaction logs, identifying data structures in the DAS for which corresponding log records exist with sequence values following the recovery sequence value;
and
applying to the identified data structures the modifications in the log records with sequence values following the recovery sequence value.

12 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/790,241Filed 8 Nov 1991
Granted: 18 Jan 1994
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

G06F 11/1471
Error detection or correction of the data by redundancy in operations: involving logging of persistent data for recovery
G06F 2201/825
Indexing scheme relating to error detection, to error correction, and to monitoring: the problem or solution involving locking
G06F 2201/87
Indexing scheme relating to error detection, to error correction, and to monitoring: monitoring of transactions
Y10S 707/99938
Database or file accessing: concurrency, e.g. lock management in shared database