Sybase Adaptive Server IQ 12.4.2, Руководство по администрированию и эксплуатации

Страница: 307 / 536

287
C H A P T E R 8
Transactions and Versioning
About this chapter This chapter describes Adaptive Server IQ’s approach to transaction
processing, called snapshot versioning, and its implications for
performance and other aspects of database administration.
Overview of transactions and versioning
Adaptive Server IQ uses transaction processing to allow many users to
read from the database while it is being updated. Transaction processing
ensures that logically related commands are executed as a unit.
Transactions are fundamental to maintaining the accuracy of your data,
and to data recovery in the event of system failure.
A crucial aspect of transaction processing is its ability to isolate users from
the effect of other users’ transactions. Adaptive Server IQ’s approach to
transaction processing, called snapshot versioning, supports the highest
level of isolation recognized by ISO.
Introduction to transactions
Transactions are simply groups of SQL statements. Each transaction
performs a task that changes your database from one consistent state to
another. These units play an important role in protecting your database
from media and system failures, and in maintaining the consistency of
your data.
Transactions are logical units of work
A transaction is a logical unit of work. Each transaction is a sequence of
logically related commands that accomplish one task and transform the
database from one consistent state into another.