MULTITENANT ARCHITECTURE AND MULTI-PROCESS AND MULTI-THREADED

 Information sourced from Oracle Docs.

The multitenant architecture capability enables an Oracle database to function as a multitenant container database (CDB). A CDB includes zero, one, or many customer-created pluggable databases (PDBs). A PDB is a portable collection of schemas, schema objects, and non-schema objects that appears to an Oracle Net client as a non-CDB. You can unplug a PDB from a CDB and plug it into a different CDB.

Large enterprises may use hundreds or thousands of databases. Often these databases run on different platforms on multiple physical servers. Because of improvements in hardware technology, especially the increase in the number of CPUs, servers are able to handle heavier workloads than before. A database may use only a fraction of the server hardware capacity. This approach wastes both hardware and human resources.

For example, 100 servers may have one database each, with each database using 10% of hardware resources and 10% of an administrator's time. A team of DBAs must manage the SGA, database files, accounts, security, and so on of each database separately, while system administrators must maintain 100 different computers.

To show the problem in reduced scale, Figure below depicts 11 databases, each with its own application and server. A head DBA oversees a team of four DBAs, each of whom is responsible for two or three databases.

Benefits of the Multitenant Architecture for Database Consolidation

The process of consolidating data from multiple databases into one database on one computer is known as database consolidation. Starting in Oracle Database 12c, the Oracle Multitenant option enables you to consolidate data and code without altering existing schemas or applications.

The PDB/non-CDB compatibility guarantee means that a PDB behaves the same as a non-CDB as seen from a client connecting with Oracle Net. The installation scheme for an application back end that runs against a non-CDB runs the same against a PDB and produces the same result. Also, the run-time behavior of client code that connects to the PDB containing the application back end is identical to the behavior of client code that connected to the non-CDB containing this back end.

Operations that act on an entire non-CDB act in the same way on an entire CDB, for example, when using Oracle Data Guard and database backup and recovery. Thus, the users, administrators, and developers of a non-CDB have substantially the same experience after the database has been consolidated.

The DBA team is reduced from five to three, with one CDB administrator managing the CDB while two PDB administrators split management of the PDBs.

We have seen another kind of consolidation in our environment. Satellite database consolidation into 2 databases, one each in the DCs, and 2 databases we created.

Using the multitenant architecture for database consolidation has the following benefits:

1.   Cost reduction

By consolidating hardware and sharing database memory and files, you reduce costs for hardware, storage, availability, and labor. For example, 100 PDBs on a single server share one database instance and one set of database files, thereby requiring less hardware and fewer personnel.

2.   Easier and more rapid movement of data and code

By design, you can quickly plug a PDB into a CDB, unplug the PDB from the CDB, and then plug this PDB into a different CDB. The implementation technique for plugging and unplugging is similar to the transportable tablespace technique.

3.   Easier management and monitoring of the physical database

The CDB administrator can attend to one physical database (one set of files and one set of database instances) rather than split attention among dozens or hundreds of non-CDBs. Backup strategies and disaster recovery are simplified.

4.   Separation of data and code

Although consolidated into a single physical database, PDBs mimic the behavior of non-CDBs. For example, if user error loses critical data, a PDB administrator can use Oracle Flashback or point-in-time recovery to retrieve the lost data without affecting other PDBs.

5.   Secure separation of administrative duties

A user account is common, which means that it can connect to any container on which it has privileges, or local, which means that it is restricted to a specific PDB. A CDB administrator can use a common user account to manage the CDB. A PDB administrator uses a local account to manage an individual PDB. Because a privilege is contained within the container in which it is granted, a local user on one PDB does not have privileges on other PDBs within the same CDB.

6.   Ease of performance tuning

It is easier to collect performance metrics for a single database than for multiple databases. It is easier to size one SGA than 100 SGAs.

7.   Support for Oracle Database Resource Manager

In a multitenant environment, one concern is contention for system resources among the PDBs running on the same computer. Another concern is limiting resource usage for more consistent, predictable performance. To address such resource contention, usage, and monitoring issues, you can use Oracle Database Resource Manager.

8.   Fewer database patches and upgrades 

It is easier to apply a patch to one database than to 100 databases, and to upgrade one database than to upgrade 100 databases.

Multi-process and Multi-threaded Oracle Database Systems

Multi-process Oracle Database (also called multiuser Oracle Database) uses several processes to run different parts of the Oracle Database code and additional Oracle processes for the users—either one process for each connected user or one or more processes shared by multiple users. Most databases are multiuser because a primary advantage of a database is managing data needed by multiple users simultaneously.

Each process in a database instance performs a specific job. By dividing the work of the database and applications into several processes, multiple users and applications can connect to an instance simultaneously while the system gives good performance.

In previous releases, Oracle processes did not run as threads on UNIX and Linux systems. Starting in Oracle Database 12c, the multithreaded Oracle Database model enables Oracle processes to execute as operating system threads in separate address spaces. When Oracle Database 12c is installed, the database runs in process mode. You must set a parameter to run the database in threaded mode. In threaded mode, some background processes on UNIX and Linux run as processes (processes containing one thread), whereas the remaining Oracle processes run as threads within processes.

In a database running in threaded mode, PMON and DBW might run as operating system processes, whereas LGWR and CMON might run as threads within a single process. Two foreground processes and a parallel execution (PX) server process might run as threads in a second operating system process. A third operating system process might contain multiple foreground threads. Thus, "Oracle process" does not always mean "operating system process."

The V$PROCESS view contains one row for each Oracle process connected to a database instance.

This document is to be read with the Oracle white paper published in defense of struggle any Service Oriented SW created, and work with those small scale businesses also.