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I think, that the oracle instance is just a serial of OS process, and a oracle database is a set of database files.

And a oracle instance can MOUNT database just like Linux can mount disks.

So, in XE we cannot run two instances, but we can create multiple databases and use the only instance to mount and unmount.

But after reading this thread, I'm confused.

lovespring
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  • What is the business problem that you are trying to solve? It would be possible in other versions of Oracle to have mount different databases serially. But that would be highly, highly unusual. It would likely be possible to get XE to do the same thing but it would probably be rather painful if you could get it to work and would certainly be a very unique configuration that might start to hit up against license restrictions as well. What other database products refer to as a "database" is much more what Oracle calls a "schema". Are you sure you don't want multiple Oracle schemas? – Justin Cave Jun 28 '14 at 00:07
  • @JustinCave I'm confused about the concept. actually, except for learning and trial, I don't want to use XE to solve any real business problems. – lovespring Jun 28 '14 at 06:24
  • Why, then, do you want to create a second database rather than using the database named XE that was created when you installed Oracle XE? What would having a second database do for you? – Justin Cave Jun 28 '14 at 06:27
  • @JustinCave when you learn something, you want learn a complete concept, at that time, you may not think out a real situation. For example, If you run a cloud, you may want diff database for diff client. – lovespring Jun 28 '14 at 06:34
  • If you were running a cloud service, you wouldn't be using XE. The simple answer, then, would be that you cannot realistically have multiple databases using XE. The longer answer is that you probably could but it would involve some hacking, wouldn't be practical, and might violate the license. – Justin Cave Jun 28 '14 at 06:38
  • @JustinCave you mean, in enterprice edition, we could run one instance, and each time when it start up, it can mount diff database? – lovespring Jun 28 '14 at 06:40
  • Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/56452/discussion-between-justin-cave-and-lovespring). – Justin Cave Jun 28 '14 at 06:40

1 Answers1

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You can only have one XE 'database' or 'SID', but you can have multiple schemas.

No. You can only have one XE database per server. You can have as many schemas in that database as you'd like. If you are coming from a background in other databases, what most databases refer to as a database is most equivalent to what Oracle refers to as a schema.

See this similar stack overflow question:

Can I have multiple databases on oracle express edition

Oracle XE is also has the following hardware limitations:

  • only use one CPU on a system
  • use up to 1GB of RAM
  • store up to 4GB of data, 11GB of data on 11.2
Community
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GoldenJam
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  • no, I don't need a schema/user, I need the really database(think about the create database statement). schema is just a divide of database. what I want to know is: Can the oracle instance mount different databases. – lovespring Jun 27 '14 at 23:55
  • You can only have one 'database' when using XE. – GoldenJam Jun 28 '14 at 00:05