Pat Shuff's Blog

resizing Amazon RDS Oracle EE

Yesterday we looked at connecting to DBaaS with the Oracle platform as a service option. We wanted to extend the database table size because we expect to grow the tablespace beyond current storage capacity. We are going to do the same thing today for Amazon RDS running an Oracle Enterprise Edition 12c instance. To start our journey, we need to create a database instance in Amazon. This is done by going to the Amazon AWS Console and click on RDS to launch a database instance. We then click on the Launch DB Instance button and click on the Oracle tab. We select Enterprise Edition then the Dev/Test for our example. We accept the defaults, define our database with ORACLE_SID=pri, username of oracle, no multi-AZ replication, and select the processor and memory size.

While the database is creating we need to change the default network configuration. By default port 1521 is open but open to an ip address range. We need to open this up to everyone so that we can connect to the database from our desktop instance. We are using a Windows 2012 instance in the Oracle IaaS cloud so the default mapping back to the desktop we used to create the database does not work. Note that since we do not have permission to connect via ssh connecting with a tunnel is not an option. We must open up port 1521 to the world and can not use a tunnel to connect these two instances. The only security option that we have is ip white listing, vpn, opening up port 1521 to the world. This is done by going into the security groups definition on the detail page of the instance. We change the default inbound rule from an ip address to anywhere.

We could have alternatively defined a security group that links the ip address of our IaaS instance as well as our desktop prior to creation of this database to keep security a little tighter. Once the database is finished creating we can connect to it. We get the connection string (DNS address) and open up SQL Developer. We create a new database connection using the sid of pri, username of oracle, and port 1521. Once we connect we can define the DBA view to allow us to manage parts of the database since we do not have access using Enterprise Manager.

It looks like the table space will autoextend into the available space, all we should have to do is extend the /rdsdata partition. This is done by modifying the RDS instance from the console. We change the storage from the 20 that we created to 40, turn on advanced monitoring (not necessary for this exercise), and check the apply immediately button. This reconfigures the database and extends the storage. Note the resize command that happens for us. This is a sysdba level command that is executed on our behalf since we do not have sys rights outside the console.

We can look at the new instance and see that the size has grown and we have more space to expand into.

We can see the changes from the monitoring console

In summary, we are able to easily scale storage in an Amazon RDS instance even though we do not have sys access to the system. We do need to use the AWS Console to make this happen and can not do this through Enterprise Manager because we can't add the agent to the instance. It is important to note that some of the options that are available from the console and some are available with altered command line options that give you elevated admin privileges without giving you system access. Look at the new command structures and decide if forking your admin tools just to run on RDS is something worth doing or too much effort. These changes effectively lock you into running your Oracle database on Amazon RDS. For example to change the tablespace definition in Oracle you would typically type

alter database default tablespace users2;

but with Amazon RDS you would need to type

exec rdsadmin.rdsadmin_util.alter_default_tablespace('users2');

Is this a show stopper? It could be or it might be trivial. It could stop some pre-packaged applications from working in Amazon RDS and you are forced to go with EC2 and S3. The upgrade storage example that we just went through would be a manual process with the involvement of an operating system administrator thus incurring additional cost and time. Again, this blog is not about A is better than B. This blog is about showing things that are hidden and helping you decide which is better for you. Our recommendation is to play with Amazon RDS and Oracle PaaS and see which fits your needs best.

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