Fast log apply

Details Fast log apply Fast log apply

1998-09-16

2001-09-11

Beausoleil, Robert (Department: 2181)

Data processing: database and file management or data structures

Database design

Data structure types

C707S793000, C707S793000, C707S793000, C714S020000

Reexamination Certificate

active

06289355

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to computer-implemented database management systems, and, in particular, to improving database recovery time after a system failure.
2. Description of the Related Art
Database management systems (DBMSs) are computerized information storage and retrieval systems. Relational database management systems (RDBMSs) are DBMSs that store and retrieve data that is organized as tables. A table consists of rows and columns of data. The rows are formally called tuples. A database will typically have many tables and each table will typically have multiple tuples and multiple columns.
A common technique for storing a database in a data storage device is to assign each table to a tablespace. A tablespace is a named collection of one or more datasets. Each tablespace is physically divided into equal units called data pages, and each data page contains one or more tuples of data.
DBMSs are susceptible to data loss after a system failure. To prevent such a data loss, DBMSs usually copy the database from a volatile storage device to a non-volatile storage device, such as a direct access storage device (DASD). Additionally, as data changes occur, DBMSs commonly record these changes in a recovery log. A recovery log is a list of time-ordered actions that indicate what changes were made to the database and in what order those changes were made. The recovery log may be stored in a data storage device, such as DASD or a buffer.
As shown in
FIG. 1
, prior art recovery techniques generally involve reading a log
102
and applying the log records
104
to an associated data page or data page set
106
. Specifically, the data page
106
is read from a buffer or from the DASD, and required changes are made to the data page
106
. This process is repeated until all the data pages
106
are read, and the database is restored to the state it was in before the system failure. Because many different log records
104
can apply to the same data page
106
, a data page
106
may be read many times. Reading a data page
106
multiple times increases the number of input/output operations and increases the log apply time. Thus, there is a need for an improved recovery technique.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a technique for restoring a database in a computer.
In accordance with the present invention, the database contains objects and is stored on a data storage device connected to the computer. After a system failure, a log file is read. The log file contains one or more modifications to the database objects. Each modification has an associated data page and time stamp or sequence number. The modifications are sorted by at least one predefined sorting key value. The sorted modifications are then grouped by database object. The sorted modifications are applied to each database object in parallel.
An objective of an embodiment of the present invention is to speed up the log apply time, and thus, improve the database recovery time after a system failure. A further objective of an embodiment of the present invention is to retain the time-ordering of database actions, while performing a log apply on multiple database objects in parallel.


REFERENCES:
patent: 5278982 (1994-01-01), Daniels et al.
patent: 5313625 (1994-05-01), Hess et al.
patent: 5377016 (1994-12-01), Kashiwagi et al.
patent: 5696967 (1997-12-01), Hayashi et al.
patent: 5740434 (1998-04-01), Eastep
patent: 5974425 (1999-10-01), Obermarck et al.
patent: 6016553 (2000-01-01), Schneider et al.
“Hardware Data Recovery at Task Level”,IBM® Technical Disclosure Bulletin, 33(6B):201-204 (Nov. 1990).
“Recovery Protocol for Nested Transactions Using Write—Ahead logging”,IBM® Technical Disclosure Bulletin, 31(4):2 pages (Sep. 1988).

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