(Continued from previous part...)

9. Different types of Transaction Isolation Levels?

The isolation level describes the degree to which the data being updated is visible to other transactions. This is important when two transactions are trying to read the same row of a table. Imagine two transactions: A and B. Here three types of inconsistencies can occur:

* Dirty-read: A has changed a row, but has not committed the changes. B reads the uncommitted data but his view of the data may be wrong if A rolls back his changes and updates his own changes to the database.
* Non-repeatable read: B performs a read, but A modifies or deletes that data later. If B reads the same row again, he will get different data.
* Phantoms: A does a query on a set of rows to perform an operation. B modifies the table such that a query of A would have given a different result. The table may be inconsistent.

TRANSACTION_READ_UNCOMMITTED : DIRTY READS, NON-REPEATABLE READ AND PHANTOMS CAN OCCUR.
TRANSACTION_READ_COMMITTED : DIRTY READS ARE PREVENTED, NON-REPEATABLE READ AND PHANTOMS CAN OCCUR.
TRANSACTION_REPEATABLE_READ : DIRTY READS , NON-REPEATABLE READ ARE PREVENTED AND PHANTOMS CAN OCCUR.
TRANSACTION_SERIALIZABLE : DIRTY READS, NON-REPEATABLE READ AND PHANTOMS ARE PREVENTED.

10. What is 2 phase commit?

A 2-phase commit is an algorithm used to ensure the integrity of a committing transaction. In Phase 1, the transaction coordinator contacts potential participants in the transaction. The participants all agree to make the results of the transaction permanent but do not do so immediately. The participants log information to disk to ensure they can complete In phase 2 f all the participants agree to commit, the coordinator logs that agreement and the outcome is decided. The recording of this agreement in the log ends in Phase 2, the coordinator informs each participant of the decision, and they permanently update their resources.

11. How do you handle your own transaction ?

Connection Object has a method called setAutocommit(Boolean istrue)
Default is true. Set the Parameter to false , and begin your transaction

12. What is the normal procedure followed by a java client to access the db.?

The database connection is created in 3 steps:
1. Find a proper database URL
2. Load the database driver
3. Ask the Java DriverManager class to open a connection to your database

In java code, the steps are realized in code as follows:
1. Create a properly formatted JDBR URL for your database. (See FAQ on JDBC URL for more information). A JDBC URL has the form
jdbc:someSubProtocol://myDatabaseServer/theDatabaseName
2. Class.forName(”my.database.driver”);
3. Connection conn = DriverManager.getConnection(”a.JDBC.URL”, “databaseLogin”,”databasePassword”)

13. What is a data source?

A DataSource class brings another level of abstraction than directly using a connection object. Data source can be referenced by JNDI. Data Source may point to RDBMS, file System , any DBMS etc.

14. What are collection pools? What are the advantages?

A connection pool is a cache of database connections that is maintained in memory, so that the connections may be reused

15. How do you get Column names only for a table (SQL Server)?

Write the Query. -

select name from syscolumns
where id=(select id from sysobjects where name='user_hdr')
order by colid --user_hdr is the table name