Oracle FAQ's Part-2

21. What is a Redo Log ?
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.

22. What is an Index Segment ?
Each Index has an Index segment that stores all of its data.

23. Explain the relationship among Database, Tablespace and Data file.?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace

24. What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.

25. What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

26. What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.

27. What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more
columns of a table.

28. What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.

29. What is a View ?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

30. What is Table ?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

31. What is a Synonym ?
A synonym is an alias for a table, view, sequence or program unit.

32. What is a Sequence ?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

33. What is a Segment ?
A segment is a set of extents allocated for a certain logical structure.

34. What is schema?
A schema is collection of database objects of a User.

35. Describe Referential Integrity ?
A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.

36. What is Hash Cluster ?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

37. What is a Private Synonyms ?
A Private Synonyms can be accessed only by the owner.

40. What is Database Link ?
A database link is a named object that describes a "path" from one
database to another.

41. What is a Tablespace?
A database is divided into Logical Storage Unit called tablespaces.
A tablespace is used to grouped related logical structures together

42. What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store "undo" information.

43. What are the Characteristics of Data Files ?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.

44. How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and can't be changed latter.

45. What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information. Database Name Names and locations of a database's files and redolog files.
Time stamp of database creation.

46.What is difference between UNIQUE constraint and PRIMARY KEY constraint ?
A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls.


47.What is Index Cluster ?
A Cluster with an index on the Cluster Key

48.When does a Transaction end ?
When it is committed or Rollbacked.

49. What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What are the factors that affect OPTIMIZER in choosing an Optimization approach ?
The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.

50. What is the effect of setting the value "CHOOSE" for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command ?
The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary.
Otherwise the OPTIMIZER chooses RULE_based approach.