It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent (number of extents is based on the optimal size)
How Will You Create Multiple Rollback Segments In A Database?
- Create a database, which implicitly creates a SYSTEM rollback segment in a SYSTEM tablespace.
- Create a second rollback segment name R0 in the SYSTEM tablespace.
- Make new rollback segment available (after shutdown, modify init.ora file and start database)
- Create other tablespaces (RBS) for rollback segments.
- Deactivate rollback segment R0 and activate the newly created rollback segments.
What Is The Functionality Of System Table Space?
To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.
What Is The Optimal Parameter?
It is used to set the optimal length of a rollback segment.
What Is The Role Of Pctfree Parameter Is Storage Clause?
This is used to reserve certain amount of space in a block for expansion of rows.
How Does Space Allocation Table Place Within A Block?
Each block contains entries as follows
Fixed block header
Variable block header
Row Header, row date (multiple rows may exists)
PCTEREE (% of free space for row updating in future)
What Is Public Database Link?
Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.
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What Is Private Database Link?
Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner’s views or procedures.
What Are The Types Of Database Links?
Private database link, public database link & network database link.
What Is Database Link?
A database link is a named object that describes a “path” from one database to another.
When Can Hash Cluster Used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.
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.
What Is The Use Of Redo Log Information?
The information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database’s data files.
What Is The Function Of Redo Log?
The primary function of the redo log is to record all changes made to data.
What Is A Redo Log?
The set of redo log files for a database is collectively known as the database redo log.
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.
What Is A Datafile?
Every Oracle database has one or more physical data files. A database’s data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
What Is A Temporary Segment?
When the statement finishes execution, the temporary segment extents are released to the system for future use.
What Are The Uses Of Rollback Segment?
To generate read-consistent database information during database recovery and to rollback uncommitted transactions by the users.
What Is Rollback Segment?
A database contains one or more rollback segments to temporarily store “undo” information.
What Is An Index Segment?
Each index has an index segment that stores all of its data.
What Are The Different Types Of Segments?
Data segment, index segment, rollback segment and temporary segment.
What Is A Segment?
A segment is a set of extents allocated for a certain logical structure.
What Are Synonyms Used For?
- Mask the real name and owner of an object.
- Provide public access to an object
- Provide location transparency for tables, views or program units of a remote database.
- Simplify the SQL statements for database users.
What Is Mean By Program Global Area (pga)?
It is area in memory that is used by a single Oracle user process.
What Is A Shared Pool?
Shared pool in oracle contains cache information that collects, parses, interprets and executes SQL statements that goes against database. This shared pool acts like a buffer for these SQL statements.
What Is Sga?
The System Global Area in an Oracle database is the area in memory to facilitate 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 pool area.
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 stored only once for multiple tables in the cluster.
What Are Clusters?
Group of tables physically stored together because they share common columns and are often used together is called cluster.
What Is A Control File?
Database’s overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable.
It Is Possible To Use Raw Devices As Data Files And What Are The Advantages Over File System Files?
The advantages over file system files are that I/O will be improved because Oracle is bye-passing the kernel which writing into disk. Disk corruption will be very less.
How Can We Plan Storage For Very Large Tables?
Limit the number of extents in the table
Separate table from its indexes.
Allocate sufficient temporary storage.
What Is A Join? Explain The Different Types Of Joins?
Join is a query, which retrieves related columns or rows from multiple tables.
Self Join – Joining the table with itself.
Equi Join – Joining two tables by equating two common columns.
Non-Equi Join – Joining two tables by equating two common columns.
Outer Join – Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.
What Is Difference Between Truncate & Delete?
TRUNCATE commits after deleting entire table i.e., cannot be rolled back.
Database triggers do not fire on TRUNCATE
DELETE allows the filtered deletion. Deleted records can be rolled back or committed.
Database triggers fire on DELETE.
What Is A Transaction?
Transaction is logical unit between two commits and commit and rollback.