PL/SQL Interview Questions And Answers
PL/SQL (Procedural Language/Structured Query Language) is Oracle Corporation's proprietary procedural extension to the SQL database language, used in the Oracle database. Some other SQL database management systems offer similar extensions to the SQL language. PL/SQL's syntax strongly resembles that of Ada, and just like Ada compilers of the 1980s the PL/SQL runtime system uses Diana as intermediate representation.
The key strength of PL/SQL is its tight integration with the Oracle database.
PL/SQL is one of three languages embedded in the Oracle Database, the other two being SQL and Java.
1. What is Shared SQL pool ?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
2. Explain database instance ?
A database instance (server) is a set of memory structures and background processes that access a set of database files.
The memory structures are used to store most queried data from database. This helps us to improve database performance by decreasing the amount of I/O performed against data file.
The process can be shared by all users.
3. What are the basic element of an oracle Database ?
It consists ofone or more data filesone or more control filestwo or more redo log files
The database containsMultiple users/schemasone or more rollback segmentsone or more tablespacesData dictionary tables
User objects (tables,indexes,views etc)
The server that access the database consists of
SGA (Database buffer, Dictionary Cache Buffers, redo log buffers,Shared SQL pool)
SMON
PMON
LGWR
DBWR
ARCH
CKPT
RECO
Dispatcher
User process with associated PGA
4. What are the factors causing the reparsing of SQL statements in SGA ?
Due to insufficient Shared SQL pool size
5. What is a cluster key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stores only once for multiple tables in the cluster.
6. What is a clusters? Explain
Group of tables physically stored together because they share common columns and are often used together is called Clusters.
7. What is a data segment ?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.
8. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table.An index is automatically created when a unique or primary key constraint clause is specified in create table command
9. What is deadlock ? Explain.
Two processes waiting to update the rows of a table which are locked by the other process then deadlock arises.
In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.
10. What is meant by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User process.
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