What are ORACLE PRE-COMPILERS?

• Using ORACLE PRE-COMPILERS, SQL statements and PL/SQL blocks can be contained inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA. 
• The Precompilers are known as Pro*C,Pro*Cobol,This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is embedded is known as the host language. 
• The pre-compiler translates the embedded SQL and pl/sql ststements into calls to the precompiler runtime library.The output must be compiled and linked with this library to create an executable.

How you can coalesce free space in oracle?

• SMON coalesces free space (extents) into larger, contiguous extents every 2 hours and even then, only for a short period of time. 
• SMON will not coalesce free space if a tablespace's default storage parameter "pctincrease" is set to 0. 
• With Oracle 7.3 one can manually coalesce a tablespace using the ALTER TABLESPACE tblspace_temp COALESCE; command, until then use 

          SQL> alter session set events 'immediate trace name coalesce level n'

          Where 'n' is the tablespace number.

          SELECT TS#, NAME FROM SYS.TS$;

• You can get status information about this process by selecting from the SYS.DBA_FREE_SPACE_COALESCED dictionary view.