orcle 12c 多租户环境Multitenant Environment

    oracle 12c 推出Multitenant Environment，多租户环境可以把以前的分散数据库整合到一块进行管理，升级，备份
新的数据库让企业可以在单一实体机器中部署多个数据库，而且每个数据库都能以动态插拔的方式，在12c多租户架构下扩充、整合、升级与备份.12c的多租户架构最多可支持252个数据库（不包含种子pdb），多租户环境通过container database (CDB) 来实现的。

多租户环境有如下好处：

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 plug a PDB into a CDB, unplug the PDB from the CDB, and then plug this PDB into a different CDB. Therefore, you can easily move an application's database back end from one server to another.

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 CDB, PDBs mimic the behavior of traditional non-CDBs. For example, if a user error causes data loss, then a PDB administrator can use point-in-time recovery to retrieve the lost data without affecting other PDBs.

5.Ease of performance tuning

It is easier to collect performance metrics for a CDB than for multiple non-CDBs. It is easier to size one SGA than several SGAs.

6.Support for Oracle Database Resource Manager

In a CDB, one concern is contention for system resources among the PDBs running on the same server. 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 (see Chapter 44, "Using Oracle Resource Manager for PDBs with SQL*Plus").

7.Fewer patches and upgrades

It is easier to apply a patch to one CDB than to multiple non-CDBs and to upgrade one CDB than to upgrade several non-CDBs.

A multitenant environment is especially useful when you have many non-CDBs deployed on different hardware in multiple Oracle Database installations. These non-CDBs might use only a fraction of the hardware resources dedicated to them, and each one might not require a full-time database administrator to manage it.

By combining these non-CDBs into a CDB, you can make better use of your hardware resources and database administrator resources. In addition, you can move a PDB from one CDB to another without requiring changes to the applications that depend on the PDB.