TYPES OF DATATYPES FOUND IN AN ORACLE DATABASE!

Types of Oracle Database Datatypes

1. varchar2 this is the most common  datatype it allows you to store  alphanumeric characters. The length of varchar2 is 4000 bytes or characters. This was what set Oracle apart from other databases in prior years. While other databases had lengths up to 2000 Oracle had its character length set at 4000
2. Number  datatype: allows you to store an interger as well as decimal values
3. date datatype not to be confused with the time stamp datatype stores the date value - the default way of storing date in Oracle is DD-MON-YY
4. Timestamp related to the date dataype but instead stoeres information witth a higher sense of precision and accuracy. It stores the date up to the second eg 14 -OCT-09 01.25.07.00002 PM
5. Clob datatype - stores large objects that are over four gigabytes in size
6. blob datatype allows for the storage of large binary objects a great example of this would be video.

Hope you enjoyed this post.

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WHAT IS THE SGA IN ORACLE AND WHAT IS IN IT??

Oracle memory is called the SGA: there are different components of the SGA. Every database will have a section within the memory (SGA) referred to as the database buffer cache!

 It is split up into little blocks in memory called the oracle data blocks. Each one of these blocks will be 8k in size.

There is an algorithm that gets applied to the database buffer pool, it is the LRU (least recently used).. As the blocks get touched they get placed toward the LRU to get written to disk, Oracle keeps the most used in memory for easier access.

Another area in the SGA is the Shared Pool which is used to reduce parsing- there are two sections within shared pool.

1. Library Cache: Inside the library Cache, you have the actual text of the sql statement .You will also have as compiled section of the SQL code which is called META CODE. The third area you have in the library  is the execution plan. This shows how the query is going to retrieve the rows.
2. The second piece of the shared pool is  the dictionary cache. It contains the names of objects that have been touched recently. Your privileges and rows is stored here too. So if the employee table has been accessed recently, it is placed in the shared pool

There are other pieces within the SGA. I will list two more in this post:

Most databases will have the JAVA pool in the SGA which stores your JAVA.

If you are using the RMAN utility in oracle you would want to configure your LARGE pool within the SGA.

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HOW DO YOU CREATE THE ORACLE PASSWORD FILE?

Oracle password file  is created using a utility called ORAPWD! You will also use this utility to make changes.

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WHAT ARE YOUR ONLINE REDO LOGS?

An online redo log tracks all of your changes to your tables.  In order to get started, you need a minimum of  two to get started on your online database; this redo log group is like a recorder, that records changes going on in your oracle database. However, you will end up having more than one group. You could end up with three groups or more.

Oracle  recommends that you multiplex your redo logs. When this redo log gets filled oracle does what is called a check point and then it writes to the next group.

This redo logs are used for database recovery. When the final group fills up it goes back to the first and writes to the first group (basically overwriting what was currently in the first group); but if you are in archive log mode, when the first group fills the information is copied onto Archived redo logs (the default is no archive log mode which overwrites the data).

If you have not archived the first log and your directory is full and you are running on archive log mode. Your  database will hang.


Here is a basic definition of an oracle database


An oracle database is  defined as three types of files, control files, data files and the redo logs! Any questions.

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THREE MOST IMPORTANT PARTS OF AN ORACLE DATABASE!

Before understanding the oracle database in depth, it is important to know the most important pieces in any database. This time we are discussing the oracle database.

1. Storage - Think of it this way, your data needs to be stored in a table, which belongs to a logical area called table space and  a table space gets mapped to a physical file called a data file. (which essentially uses disk storage).
2. Memory - This is called the System global Area (SGA) in Oracle.
3. Processes - The third piece in an Oracle database is the disk processes.

Datafiles store tables, indexes and rollback segments (undo segments in 9i on wards) and temporary files. 

The most important logical  view for a DBA is the dba_data_files - this has information about the datafiles.

Another file that controls the structure of your database is your datafiles. It is recommended that you have at least 3 control files on sepererate disk drives. This shows how when your database got created etc All three control files need to look exactly alike.

There is a v$ that will tell you the path of your control file and this is the v$controlfiles.

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