Sunday 8 February 2015

Memory Management in Unix Interview Question and Answers for freshers and experienced pdf

Below are some important Memory Management interview questions which are asked in most MNC company interviews for beginners or professionals.

31. What is use of rollback segments in Oracle database?
When a user updated a particular table (for example 100 rows) the old value will be retained in the roll back segments(Oracle 8) and now it is Undo segment (oracle 9i). If the user issue a rollback command the old value will be taken from the rollback segment(that too if undo_retention parameter set properly in the parameter file).

32. What is advantage of having disk shadowing / mirroring?
Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk.
Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.

33. How redo logs can be achieved?
LGWR process wirtes all change vectors from theredo log buffer to online redo log file sequentially.

34. What is redo log file mirroring?
Multiplexing Redo log file called Mirroing. ( Keeping multiple copies in different disks)

35. How to implement the multiple control files for an existing database?
1. Edit init.ora file set control_files parameter with multiple location
2. shutdown immediate
3. copy control file to multiple locations & confirm from init.ora contol_files parameter
4. start the database.
5. run this query for changes confirmation - select name from v$controlfile;

36. What is SGA? How it is different from Ver 6.0 and Ver 7.0?
The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information between users. It holds the most recently requested structural information about the database. The structure is Database buffers, Dictionary cache, Redo Log Buffer and Shared SQL pool (ver 7.0 only) area.

37. What is a 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.

38. What is mean by Program Global Area (PGA)?
It is area in memory that is used by a Single Oracle User Process.

39. List the factors that can affect the accuracy of the estimations?
The space used transaction entries and a deleted record does not become free immediately after completion due to delayed cleanout.
Trailing nulls and length bytes are not stored. Inserts of, updates to and deletes of rows as well as columns larger than a single datablock, can cause fragmentation and chained row pieces.

40. What are the different kind of export backups?
Full back - Complete database
Incremental - Only affected tables from last incremental date/full backup date.
Cumulative backup - Only affected table from the last cumulative date/full backup date.
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