What is Oracle Grid Infrastructure – A Free Tutorial

What is Grid Infrastructure? (Hint: It is not Grid Control.)

It is still possible to run an Oracle database without Oracle Grid Infrastructure. But is it sensible?  And, if you want to use ASM – which we strongly recommend – you need GI!

In this tutorial you will learn how Grid Infrastructure can replace (or complement) third party products for RAID, network management, and high availability. At the same time, using these facilities can improve performance dramatically. Grid Infrastructure is the way Oracle is moving, and we want to show you that it is not necessarily complicated and can indeed make your life simpler. It can also save you money.

Content: live demonstrations of configuring and using Grid Infrastructure services with release 11g.

Audience: DBAs looking for entry level knowledge of what Grid Infrastruture can do.

Presenter: John Watson, Oracle Certified Master DBA

This free training is segmented into several separate lessons:

  1. Introduction (1:35)
  2. Why All Administrators Need to Know Grid Infrastructure (3:27)
  3. Intro to Network Administration with Grid Infrastructure (3:18)
  4. Demonstration – Network Administration with Grid Infrastructure (5:46)
  5. Network Administration with Grid Infrastructure Q & A (3:28)
  6. Grid Infrastructure Licensing Tips (1:21)
  7. Grid Infrastructure Storage Management, ACFS, the Cloud File System (5:00)
  8. Demonstration: ACFS, Cloud File System, Storage Management (4:02)
  9. High Availability with Oracle Grid Infrastructure (10:50)
  10. SQL Net Listening Architecture and SCAN (4:26) (click on video below)
  11. Conclusion: Planning for Oracle 11g / 12c Grid Infrastructure (1:16)

Date: Feb 21, 2013

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SQL Net Listening Architecture and SCAN

>> John:  The SQL Net Listening Architecture we get with grid infrastructure. It’s a two tier listening structure. 


There’s this thing known as the SCAN. The SCAN stands for single client access name. It’s one name resulting to three addresses. The idea of the single client access name is it’s a single, stable name that’s used by all users. 


In this particular case, the single client access name that I created – well, if I do nslookup of – it was called goldcluster-scan.goldcluster.example.com. That’s the name that I created as my single client access name. It’s the name that all clients are meant to use, the single name to use by the clients.


It resolves the three addresses, DHCP-assigned addresses. Three addresses the fault tolerance. These addresses will be brought up on one machine or another. 


The Grid Infrastructure of course will decide. I can see right now my three SCAN VIPs. One of them is on gold2, two of them are on gold1. So they get distributed across the cluster. 




On each of those listening addresses, we start a SCAN listener, a database listener at that point. Then the purpose of the SCAN then, it’s a stable name – a stable name that all users use. So whenever a client uses a connect string, it will ask for the SCAN. The SCAN will resolve to one of those three highly available addresses that will failover from one node to another. And then the SCAN listener performs redirection to a node listener. The node listener is what will actually connect you to a database itself. 


Looking at my environment here, I go to say 




Where I have my database running. 




This was the cluster where I assigned my server – my database to a server pool. I crashed one machine and resolved database failover. At this point I really have absolutely no idea as an end-user where that database actually is. But that doesn’t matter. Because of the single client access name, the SCAN, I can issue like normal connect string to connect the system manager. 


The SCAN name at incluster-scan.incluster.example.com. Now it’s on port 1521. It’s on default. The database service is Rdb. 




I have no idea what that thing actually is. But it worked.




So what happened in that flow? Well, that connect string, that was resolved by the DNS into one of three addresses. There are addresses being DHCP-assigned virtual addresses. But the DNS was updated by Grid Infrastructure. So that actually worked.




Then having contacted the SCAN listener on one of those three highly available addresses, Grid Infrastructure took it a step further and said, “What do you actually want?” You want something called Rdb and connected me to the appropriate instance wherever it happened to be. But I really didn’t know it was all completely automated.


That’s the beauty of it. If we configure a session that is automated, if we configure the session failover, it can be transparent to the clients. As I mentioned, the response to that earlier question, with the current release, transactions cannot failover. So they would have to be – they will be rolled back. Your application software would have to handle that.


But the session itself will be failover automatically. That will work not just for RAC. It will work for single instance databases. As I demonstrated, it will work for failover from primary to stand by your Data Guard environment. The listening architecture is an important part of this.     



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