Oracle architecture v DB2 architecture

Author: David (DBA)

This article makes direct comparison between the Oracle architecture (instance, databases, physical files, network, configuration files, etc) and the DB2 architecture thus allowing Oracle DBAs to understand the similarities and differences between Oracle and DB2.

Because of its comparative nature (showing you how the same things work in DB2 compared to Oracle) I think its a great first read if you are an Oracle DBA new to DB2.

I do have some comments I would like to add:

1) IBM says:

DB2 does contain a binary file known as the system database directory that contains entries of all the databases you can connect from your DB2 machine.

This compares best to Oracle tnsnames.ora file. I don't understand why IBM didn't draw this comparison.

2) IBM says:

Every Oracle database contains a table space named SYSTEM, which Oracle creates automatically when the database is created. Other table spaces for user, temporary and index data need to be created after the database has been created, and a user needs to be assigned to these table spaces before they can be used.

While I get IBMs point (that you have to create tablespaces manually after the create database command) This is not technically true. Frist, when you issue a create database command in Oracle you explicitly specify the creation of a temp tablesapce. Second, after the database creation all other tablespaces you have created can be used without being "assigned to users" simply by using them in the storage clause of the object creation statement.

3) IBM Says:

DB2 table spaces can be classified as SMS (system-managed spaces) or DMS (database-managed spaces). SMS table spaces are managed by the operating system and can only be directories. They grow automatically as needed; thus SMS provides good performance with minimum administration.

Oracle does not have the SMS concept for its storage model but its data files are similar to DB2 DMS table spaces.

This is not entirely true. There is something similar (but not completely) in Oracle known as OMF(9i)/ASSM(10g). I will not go into detail about what these features do, but I will say that while OMF / ASSM files are managed by Oracle and no the Operating System, they do simplify the administration of tablespaces to an almost automatic level.

4) IBM Says:

As indicated earlier, Oracle's data buffer concept is equivalent to DB2's bufferpool; however, DB2 allows for multiple bufferpools to exist. There is no predefined number of bufferpools that you can create, and they can have any name.

Again, not entirely true. While less flexible, Oracle 9i/10g allows for multiple db buffers with different block size. The limitation is one buffer per one block size while in DB2 it is one buffer per tablespace.


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