View data in a datafile.

SQL> create tablespace testts datafile '/tmp/testts_01.dbf' size 1M;

SQL> create table mythbuster1 (col1 varchar2(200)) tablespace testts;

Insert a row:

SQL> insert into mythbuster1 values (‘ORIGINAL_VALUE’);
SQL> Commit; 

$ strings /tmp/testts_01.dbf
}|{z
-N?pD112D2
TESTTS
 1j)
 w>!
ORIGINAL_VALUE
 

Wait event.

The server process then identifies the block the row exists in. After 
the database instance just came up the buffer cache is empty and the 
block will not be found. Therefore the server process issues a read call
 from the datafile for that specific block. The block is read from the 
disk to the buffer cache.

Until the loading of the block from the disk 
to the buffer cache is complete, 

the session waits with the event – db file scattered read. 

Two Task Architecture 

 There are two tasks – the 
user task that a regular user has written and the server task that 
performs the database operations. This is an important concept 
established during the early foundations of the Oracle database to 
protect the database from errant code in the user task introduced either
 maliciously or inadvertently.
 

usertask=user processes=Java program, a Pro*C code, SQL*Plus process

server task=server processes=oracleinstance