Books for you

However, to make it perfectly clear how these
features interact, we??™ll walk you through three scenarios: a simple write to the database,
a situation in which two users attempt to write to the same row in the same
table, and a read that takes place in the midst of conflicting updates.
For the purposes of these examples, we??™ll use the scenario of one or two users modifying
the EMP table, a part of the standard sample Oracle schema that lists data
about employees via a form.
A Simple Write Operation
This example describes a simple write operation, in which one user is writing to a
row in the database. In this example, an HR clerk wants to update the name for an
employee. Assume that the HR clerk already has the employee record on-screen. The
steps from this point are as follows:
1. The client modifies the employee name on the screen. The client process sends a
SQL UPDATE statement over the network to the server process.
2. The server process obtains a System Change Number and reads the data block
containing the target row.


Pages:
409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433