NEW! Details on the Final Exam (Posted June 1)

The Final Exam will be held Friday, June 8. Here is the page about the Final, including a link to the answers to the Midterm (which you should study!).

Details on the Midterm Exam (May 13th)

The Midterm Exam will be held Tuesday, May 15th. The Midterm will cover the material covered on the first two quizzes, plus locking, especially the material on locking that is posted and was handed out. In addition, there will be one or two questions about the write-ahead log, the material at the beginning of Chapter 25, through page 923 (actually through the top line on page 924). I will discuss this material in class on Monday the 14th.

Quiz #2 -- Primarily focused on Chapters 15 and 23

A one-half hour quiz held on Thursday, May 3rd.

A rough guide to the quiz is to think of it as being made up with questions such as were on Quiz #1 and Assignments #1 and #2. A more detailed guide is the list below.

• The four isolation levels in Chapter 15. One way to think of these is in terms of locking strategies.
  
  
  • Level 0 (Read Uncommitted) uses no locks.
  • Level 1 (Read Committed) uses short read locks but long write locks.
  • Level 2 (Repeatable Read) uses long read and write locks.
  • Level 3 (Serializable) uses long locks on entire tables to avoid phantoms.
  
  
  
• Your reading should include Chap. 15 through page 489.



• Your reading should ALSO include the section on atomicity and durability, Secs. 15.2, 15.2.1 and 15.2.2. These focus on the log file with update records, checkpoint records, etc. The reason a checkpoint record is needed is explained on pg. 496 -- a Begin record is not enough, because there is no way to tell how far back to scan to find it, especially if that transaction has made no reads or writes for a very long time. A backwards scan to before the checkpoint will find the Begin record or another checkpoint, and so forth. The detailed justification for a write-ahead log is also given here, in Sec. 15.2.1.



• Chapter 20 is worth reading as an overview that brings a lot of concepts together to help your overall understanding of the material. There will be no questions on the Quiz that are based specifically on this Chapter, 20.



• The material in Chapters 21 and 22 WILL NOT be on the Quiz.



• Along with Chapter 15, the material in Chapter 23 is quite important. Specifically, you should understand the material up to, but not including Sec23.5 on pg. 833. But SKIP Sec. 23.1.2 on View Equivalence.



• You will not be asked any details of the proof of the theorem on Schedule Equivalence, which occupies parts of pgs. 818 and 819.



• You should understand the concept of serializability, knowing how to identify and construct schedules that are or are not serializable.



• You should understand serialization graphs including how to construct one from a schedule as well as constructing a schedule from a graph. (There are arbitrarily many schedules that you can construct that correspond to a given serialization graph. You would only be asked to invent one or two.) You should understand cyclic versus acyclic graphs and what they mean in this context.



• In Sec. 23.2, first understand how serialized transactions need to be constrained further to operate correctly in the presence of aborts. Learn what has to be done to create a recoverable schedule. This may lead to aborts and cascaded aborts. Know how dirty writes can arise when transactions abort in certain situations. Strictness is introduced on pg. 826, though it is only fully defined in the middle of pg. 837 as requiring write locks to be held until commit (or abort) time and to have any release of read locks occur in a two-phase manner.



• After all the discussions of the problems that can arise with simpler concurrency rules, the chapter finally converges on the pessimistic strategy of using locks, as in Fig. 23.12. But now you should understand and appreciate them much better than after the brief discussion of them in Chapter 15. So study the material in Secs. 23.3 and 23.4, ending near the end of pg.833.

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