Yes we can decrease the size of the datafile to the place where the extents are deallocated in to it by resizing the datafiles to something smaller than current. If the data in the datafile is scattered than reorg the object in the tablespace to deallocate the extent and decrease the filesize
We can reduce the size of the datafile till the high watermark of the datafile. IF we have to bring down the high watermark then we have to check the extents in the file and reorganize objects as required.
A database instance (Server) is a set of memory structure and background processes that access a set of database files.
The process can be shared by all users.
The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.
A synonym is an alternative name for objects such as tables, views, sequences, stored procedures, and other database objects.
A synonym (synonym-name) is an alias for an object (such as a table). The object does not need to exist at the time of its creation. Synonyms can't be used in a drop and truncate statements. If this is tried, it results in a ORA-00942: table or view does not exist
The syntax for creating a synonym is:
create [or replace] [public] synonym [schema .] synonym_name
for [schema .] object_name [@ dblink];
The or replace phrase allows you to recreate the synonym (if it already exists) without having to issue a DROP synonym command.
The public phrase means that the synonym is a public synonym and is accessible to all users. Remember though that the user must first have the appropriate privileges to the object to use the synonym.
The schema phrase is the appropriate schema. If this phrase is omitted, Oracle assumes that you are referring to your own schema.
The object_name phrase is the name of the object for which you are creating the synonym. It can be one of the following:
view materialized view
sequence java class schema object
stored procedure user-defined object
Type of Synonym are:-
Public (Accessible to all)
Private (Accessible to owner)
Multiple instances accessing the same database (Only In Multi-CPU environments)
Character functions analyze and modify the contents of CHAR and VARCHAR2 string variables.
Numeric functions are a full range of operations that manipulate numbers, including trigonometric, logarithmic, and exponential functions.
Date functions are utilities that allow programmers to perform high-level actions on date variables, including date arithmetic.
Conversion functions convert from one datatype to another, often formatting the output data at the same time.
LOB functions allow operations on LOB (large object) data.
Miscellaneous functions perform operations that don't fall into any of the other categories.
Example of built in functions:
1. to_date - a convertion function that will convert a string date to a date datatype
2. sum - a group function that will return the summation of all values in the column
3. upper - a single row function that will return all characters in a column in upper case
The use of RollBack Segment is Database is - to maintain read consistency between multiple transactions.
Rollback segments are the areas in your database which are used to temporarily save the previous values when some updates (by 'updates', inserts or deletes as well) or any other transactions going on.
Two processes wating 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.
Deadlock is a kind of situation,which occured in a network of database environment while multiple processes is waiting for their completion, whereas some other process is still running till the time we use the rollback or commit commands or stopped the blocked process by database systems program itself.
information about the database,redologfile and datafile,archivelog file location and current scn no
and redo log file
1. Database name and identifier.
2. Time stamp of database creation.
3. Tablespace names.
4. Backup information.
5. Checkpoint information.
6. Current online redo log file sequence numbe