Oracle supports 3 transaction isolation levels: 

- Read committed (default)

- Serializable transactions

- Read only

SQL> ALTER USER user_name ACCOUNT LOCK;

SQL> ALTER USER user_name ACCOUNT UNLOCK;

- Online backup is one which is taken at the time the database is running in the ARCHIVELOG mode.

- Following files should be backed up during the Offline Backup: All data file, all control file and all online redo log file. But in the case of the online backup following files is backed up: All data files all archived redo log files and one control file via the alter database command.

- Offline database we cannot rely upon but in case of online database no issues.

- Offline backup no archived mode is required but in the online backup it is must.

The backup strategies that are provided by Oracle are as follows:

- Logical backup using Exports and import.

- Physical file system backup

- RMAN Recovery Manger which is also known as incremental files system backup.

We use SQLPASSTHROUGH options when we need applications to access data both in the front-end and back-end data servers with a single connection. SQL statements that cannot be executed in the solidDB front-end server are passed over to the back end. 

SQLPASSTHROUGH mode can be set as per session or per transaction. The connection between the front end and back end is made with a back-end compatible ODBC driver which is loaded dynamically in solidDB server.

Basic Replication : Basic replication is implemented using standard CREATE SNAPSHOT or CREATE MATERIALIZED VIEW statements. It can only replicate data and not procedures, indexes replication is always one-way, and snapshot copies are read only.

Advanced Replication : Advanced replication supports various configurations of updatable snapshot, multi-master and update anywhere replication. It is more difficult to configure but allows data and other database objects like indexes and procedures to be replicated.

Differences between Basic and Advanced replications:

- With basic replication, data replicas provide read-only access to the table data whereas advanced replication features extend the capabilities of basic read-only replication by allowing applications to update table replicas throughout a replicated database system.

- With Basic Replication applications can query data from local data replicas. On the other hand with advanced replication, data replicas anywhere in the system can provide both read and update access to a table's data.

The following are the areas of concern for tuning:

- Memory Usage

- Data Storage

- Data Manipulation

- Physical Storage

- Logic Storage

- Network Traffic

Tuning Memory Usage: In Oracle 10g, we can use the Automatic Workload Repository (AWR) toolset to gather and manage statistical data but in case of Oracle 11g, we can use new initialization parameters such as MEMORY_TARGET to further control the overall memory used by Oracle. It helps us to tune the database automatically when we don’t have time to read the AWR report.

Tuning Data Manipulation: There are two ways to tune Data manipulation in Oracle one way is through Conventional Path mode and second is Direct Path mode.

Tuning Physical Storage: We need to tune the physical storage because it limits the disk in database. This can be done by: Distributing I/O, Striping and Mirroring.

We need to first login to the data base as: SQLPLUS followed by user_name/password. Then we need to execute the following query:

CREATE USER user_name IDENTIFIED BY abcd; in this query a user_name suggest the user that is created which has a password abcd which is required for login in database.