PART 2. Relational Database Concepts
You can group SQL statements into units called transactions. Transactions are simply groups of SQL statements with the property that either all or none of the group is executed. You should design each transaction to perform 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.
When several people use the same database at the same time, problems can occur. Adaptive Server Anywhere uses transactions in conjunction with locks to prevent or eliminate inconsistencies. A lock limits the access of other transactions to a particular row of a table.
This chapter describes transactions and how to use them in applications. It also describes the locking mechanisms at your disposal.
An overview of transactions
Introduction to concurrency
How locking works
Isolation levels and consistency
Understanding and choosing isolation levels
How Adaptive Server Anywhere implements locking
Savepoints within transactions
Particular concurrency issues
Replication and concurrency