Getting Started with DB2 Express-C

Chapter 13 – Concurrency and Locking 219
13.3.3 Non-repeatable read
A non-repeatable read implies that you cannot obtain the same result after performing the
same read in the same operation.
Figure 13.6 – Non-repeatable Read
In Figure 13.6, consider if you are trying to book a flight from Dallas to Honolulu. The
sequence of events is:
1. App1 opens a cursor (also known as a result set) obtaining what you see in Figure 13.6
2. App2 deletes a row that qualified for the cursor (for example, the row with destination
“San Jose”)
3. App2 commits changes
4. App1 closes and reopens the cursor
In this case, since App1 would not get the same data on a repeated read, it cannot
reproduce the data set; that’s why this problem is called “non-repeatable read”.
13.3.4 Phantom read
The phantom read problem is similar to the non-repeatable read problem, but the
difference is that on subsequent fetches, you may obtain additional rows rather than fewer
rows. Figure 13.7 provides an example of this problem.