Database Reference
In-Depth Information
Logical Architecture of Oracle Database
Physically the data inside the database resides in the data files
located on hard drives and if you want you can copy them to
different location but remember you cannot read those files by
yourself. The data in data files are encrypted and can only be
understandable to Oracle Instance, so if you want to take
anything out from those data files you first have to make the
Oracle Instance alive and then you have to present your
credential (username/password) to the Instance and based on
your access level your data related wishes will get fulfilled.
Logically the data inside the database resides inside the
tablespaces. Each tablespace is comprised of segments. Oracle
Instance allocates a segment each time you create a object (table,
view etc) inside the database. Each segment is composed of
Extents and What are Extents? Each extent is a group of
contiguous DB Blocks. Now what are DB Blocks? A DB Block
is the smallest building block of the database and is usually the
even multiple of OS Block e.g. DB Block can be (2 * OS Block)
but not (1.37 * OS Block). The size of the DB Block can be
specified using DB_BLOCK_SIZE init.ora parameter. You can
assign values like 2KB (2 Kilo Byes) and if the OS permits you
can have 4KB, 8KB etc.
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