Techniques for increasing the usefulness of transaction logs

Abstract

Techniques for making light-weight checkpoints in logs of streams of transactions and for extending the logs from the checkpoints. The state saved in the light weight checkpoint need only include the state of all transactions that are active at a prior point in the log and are still active at the checkpoint. A log is extended from the checkpoint by processing new transactions in the transaction stream beginning at the prior point to produce the extending log. When the checkpoint is reached, the state saved at the checkpoint is used to continue to produce the extending log. Techniques are further disclosed for selecting points in the stream of transactions at which the checkpoints may be made and for determining the distance between checkpoints. As disclosed, the log in which the checkpoints are used is a logical log made from a physical log produced by a relational database system. The logical log may be used for replication and for data mining.

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 10 / 414,591, filed on Apr. 16, 2003, pending, the entire disclosure of which is expressly incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates generally to the redo logs used in database systems to log the transactions performed by the database system and more specifically to increasing the usefulness of redo logs for purposes such as data mining and replication of transactions.[0004]2. Description of Related Art: FIG. 1[0005]Nowadays, businesses, governments, and large organizations generally are completely dependent on their database systems. If the database system fails, the organization cannot operate. Because organizations depend so completely on their database systems, the database systems must be reliable. One way in which reliability is achieved in database systems is careful design to reduce har...

AI Technical Summary

Benefits of technology

The patent describes techniques for making a log of a stream of transactions by selectively saving state at points in the stream where a checkpoint is needed. The checkpoint is a light-weight reference point that allows for the efficient and safe extension of the log. The technique can be used in various database systems and can be adapted for replication or data mining purposes. The technical effects of the patent include improved performance and efficiency in log processing and analysis.

Problems solved by technology

If the database system fails, the organization cannot operate.

In database systems that handle a large number of transactions, making such a checkpoint is expensive both as regards the time required to make the checkpoint and as regards the checkpoint's size.

A log miner could of course always begin with a copy of a data block from a physical redo log and use information from the data dictionary to determine what table the changed data block belonged to and from the kind of change what kind of database operation had been performed, but doing so was time consuming and mistake prone.

While logical redo logs have made the information contained in physical redo logs much more accessible and usable, problems still remain in the area of checkpointing.

The problems with checkpointing result in two further problems with logical redo logs:when mining the logical redo log, the user cannot extend the range of physical redo log records being mined during a mining session; andthe user cannot tune checkpoint insertion such that restoring a system using the logical redo log takes a relatively constant amount of time.

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