it360 lab - Transactions and concurrency

IT360 Lab 12 Locks and Transactions

DUE: May 5, 2010, BEFORE start of class

This lab should get you familiarized with transactions and concurrency-related problems.

The first part of this lab requires you to use transactions in MySQL and answer some questions. The second part requires you to just answer questions on paper. Write the answers to each of the following exercises in a file called yourlastname_Lab12.txt

Part 1:

For this lab, we will use the MySQL database server on cardhu.cs.usna.edu instead of schooner.cs.usna.edu. Your username and password is the same as the one you have for schooner.

Connect to your MySQL database on cardhu.cs.usna.edu using MySQL Query Browser.

Preamble: MySQL supports several types of storage engines, or table types. This means that you have a choice in the underlying implementation of the tables. The default storage engine is MyISAM, which does not support foreign keys (it ignores the foreign key declaration, instead of enforcing the foreign key referential integrity constraint) and does not support the ACID transactions we covered in class. InnoDB is another storage engine. InnoDB supports transactions and foreign key constraints. For this lab, we will use the Product table, but with the InnoDB storage engine.

1) Re-create the Product table in your new database on cardhu.cs.usna.edu, but this time the table will use the InnoDB table engine instead of the default MyISAM engine.

create table Product(

BarCode int not null,

PName varchar(50) null,

Price double not null,

QuantityInStock double not null,

Constraint pk_product PRIMARY KEY(BarCode)

)Engine = InnoDB;

2) Remember that when using transactions, the effects of the current transaction should not be visible outside the transaction until the transaction terminates (commits). Also, if a transaction aborts (rollback), the effects of the transaction are “undone”. For this exercise you will experiment with this behavior.

Start a transaction by clicking the “Transaction à” button in the MySQL Query Browser tool bar.

Insert one product in the Product table, by executing an insert statement appropriate for your table. For example,

INSERT INTO Product(BarCode, PName, Price, QuantityInStoc) VALUES(5, ‘Bagel’, 0.99, 100) would insert one Product with BarCode 5 in my Product table. If needed, change the insert statement appropriately to insert into your table.

Check that the item was inserted by executing a Select statement, for example

SELECT * FROM Product

Open now a new MySQL Query Browser session by starting MySQL Query Browser and connecting to your database on cardhu.cs.usna.edu

Check the content of the Product table executing a Select statement, for example

SELECT * FROM Product

a) Do you see the product that you just inserted in the other session? (write the answer in yourlastname_lab12.txt)

b) Why? (write the answer in yourlastname_lab12.txt)

Go back to your first MySQL query browser session and click on the “Check” (Commit Transaction) button.

Go now to the second MySQL Query Browser session and check thecontent of the Product table executing a Select statement, for example

SELECT * FROM Product

c) Do you see the product that you inserted in the other session? (write the answer in yourlastname_lab12.txt)

d) Why? (write the answer in yourlastname_lab12.txt)

Part 2:

The questions in this part are related to possible operations in the Online Store database. Of special interest for this lab are the following four tables (slightly modified for this lab only):

Product(BarCode, PName, Price, QuantityInStock)

Customer (CustomerID, Phone, Email, FirstName, LastName)

Sale (SaleID, DeliveryAddress, CreditCard, CustomerID)

SaleItem (SaleID, BarCode, Quantity)

Assume that the following three types of transcations can run concurrently in your application (could even have multiple transactions of the same type running concurrently):

create_product: creates new rows in Product table for the new products that will be sold in the store. This procedure uses only the Product table to insert new products.

create_modify_sale: records new or modifies existing customer sale and sale-product information. This procedure writes to the Sale and SaleItem tables, updates the Product table, and may be reading from the Customer and Product tables.

create_customer: records new customer data. This procedure uses only the Customer table to insert new customers.

1) Give a scenario that leads to a possible dirty read among this group of stored procedures, or explain why a dirty read cannot happen in this group of stored procedures.

2) Give a scenario that leads to a possible non-repeatable read among this group of stored procedures, or explain why a non-repeatable read cannot happen in this group of stored procedures.

3) Give an example of a possible phantom read among this group of stored procedures, or explain why a phantom read cannot happen in this group of stored procedures.

4) What transaction isolation level would you use for each of the three procedures above, and why? For each procedure you should use the least restricted transaction isolation level that ensures correctness.

Part 3

Which of the given problems can occur if the following transactions run concurrently?

T1: X(A), R(A), W(A), X(B), R(B), W(B), Commit

T2: X(B), R(B), W(B), S(A), R(A), Abort

X - acquire exclusive lock, S – acquire shared lock, R – read, W – write. All locks are released during commit or abort.

YES NO Why?

Deadlock ____ ____ ____________________________________

Dirty read in T1 ____ ____ ____________________________________

Nonrepeatable read in T2 ____ ____ ____________________________________

Lost update in T1 ____ ____ ____________________________________

Turn in (due before start of class on May 5, 2010):

Electronic:

Upload yourlastname_lab12.txt with all your answers to the Lab 12 assignment on the blackboard.

Hard-copies:

The completed assignment coversheet. Your comments will help us improve the course.
A hard copy of your yourlastname_Lab12.txt containing the answers for each exercise.