The questions are based on the following relational schema:

Emp( eid: integer, ename: string, age : integer, salary: real, did:
integer )

Dept( did: integer, dname: string, floor : integer)

and on the following update command:

replace(salary=1.1*EMP.salary) where EMP.ename=’Santa’

a. Give an example of a query that would conflict with this command
(in a concurrency control sense) if both were run at the same time.
Explain what would go wrong, and how locking tuples would solve the
problem.
b. Give an example of a query or a command that would conflict with
this command, such that the conflict could not be resolved by just
locking individual tuples or pages, but requires index locking.
c. Explain what index locking is and how it resolves the preceding
conflict.

Hello Eksolutions,

A very interesting question to research. If you search with the
phrases
  database update query conflict locking tuples
on Google, the highest ranking match has homework answers to a very
similar question (and the original PDF has been moved or deleted). It
is available from the Google cache at:
http://216.239.39.100/search?q=cache:4SdiXL-oEBQC:www.cs.columbia.edu/~gce3/4111m02/docs/hw5sol.pdf+database+update+query+conflict+locking+tuples&hl=en&ie=UTF-8

Scroll down near the end to question #4 (items a, b, and c).

In the same way, the second ranking match at
  http://www.cs.ualberta.ca/~yuan/courses/391/02fall/assignment/solasn01sp/
has question #8 which appears to be the same question with a slightly
different set of answers (and doesn't answer your "c").

The remaining references provide additional material to explain the
concepts involved.

  --Maniac

---

Request for Answer Clarification by eksolutions-ga on 04 Dec 2002 17:48 PST

How do you know that the question 4 in the first link you have
provided is the same question as mine?

---

Clarification of Answer by maniac-ga on 04 Dec 2002 18:22 PST

Hello Eksolutions,

To answer "How do I know it is the same question?"...

Use the search query I provided
  database update query conflict locking tuples

with Google. You should get the PDF file I referred to in the answer
as well as a related page from the same site. Look at the related page
in the Google cache at
http://216.239.51.100/search?q=cache:1GCrRCC51E4C:www.cs.columbia.edu/~gce3/4111m02/docs/hw5.pdf+database+update+query+conflict+locking+tuples&hl=en&ie=UTF-8

to see the original questions. I should have checked and included that
reference in my original answer. Sorry.

The clue I had to the "similar" question was the arithmetic in the
answers where the query has both a *2 and *1.1 in the calculations.
The answers also fit the questions you provided.

  --Maniac