DB2 Interview Questions

What are the disadvantages of PAGE level lock?
High resource utilization if large updates are to be done

What is lock escalation?

Promoting a PAGE lock-size to table or tablespace lock-size when a transaction has acquired more locks than specified in NUMLKTS. Locks should be taken on objects in single tablespace for escalation to occur.

 What are the various locks available?
SHARE, EXCLUSIVE, UPDATE
Can I use LOCK TABLE on a view?
No. To lock a view, take lock on the underlying tables.
What is ALTER ?
How do you simulate the EXPLAIN of an embedded SQL statement in SPUFI/QMF? Give an example with a host variable in WHERE clause.)
Use a question mark in place of a host variable ( or an unknown value ). e.g.
SELECT EMP_NAME
FROM EMP
WHERE EMP_SALARY > ?
 What are the isolation levels possible ?
CS: Cursor Stability
RR: Repeatable Read
 What is the difference between CS and RR isolation levels?
CS: Releases the lock on a page after use
RR: Retains all locks acquired till end of transaction
 Where do you specify them ?
ISOLATION LEVEL is a parameter for the bind process.
 When do you specify the isolation level? How?
During the BIND process. ISOLATION ( CS/RR )…
I use CS and update a page. Will the lock be released after I am done with that page?
No.
What are the various locking levels available?
PAGE, TABLE, TABLESPACE
 How does DB2 determine what lock-size to use?
1. Based on the lock-size given while creating the tablespace
2. Programmer can direct the DB2 what lock-size to use
3. If lock-size ANY is specified, DB2 usually chooses a lock-size of PAGE

DB2 Interview Questions and answers

DB2 Interview Questions and answers
What is a DBRM, PLAN ?
DBRM: DataBase Request Module, has the SQL statements extracted from the host language program by the pre-compiler.
PLAN: A result of the BIND process. It has the executable code for the SQL statements in the DBRM.
What is ACQUIRE/RELEASE in BIND?
Determine the point at which DB2 acquires or releases locks against table and tablespaces, including intent locks.
What else is there in the PLAN apart from the access path?
PLAN has the executable code for the SQL statements in the host program
What happens to the PLAN if index used by it is dropped?
Plan is marked as invalid. The next time the plan is accessed, it is rebound.
What are PACKAGES ?
They contain executable code for SQL statements for one DBRM.
What are the advantages of using a PACKAGE?
1. Avoid having to bind a large number of DBRM members into a plan
2. Avoid cost of a large bind
3. Avoid the entire transaction being unavailable during bind and automatic rebind of a plan
4. Minimize fallback complexities if changes result in an error.
What is a collection?
a user defined name that is the anchor for packages. It has not physical existence. Main usage is to group packages.
In SPUFI suppose you want to select max. of 1000 rows , but the select returns only 200 rows.
What are the 2 sqlcodes that are returned?
100 ( for successful completion of the query ), 0 (for successful COMMIT if AUTOCOMMIT is set to Yes).