Oracle offers Real Application Clusters (RAC) for businesses of all shapes and sizes. It offers scalability, great pricing, high performance, and max user concurrency with around-the-clock availability. Because of its structure, RAC is often considered to be a best solution for those who have critical databases.
Although an RAC license is required to gain access to this system, it is able to integrate multiple components to generate solutions that you need.
As with any system such as this, there are certain advantages and disadvantages which must be considered before making the final investment.
List of the Advantages of Oracle RAC
1. Certain patches can be applied in its rolling mode.
In rolling patching, each node is shut down in Oracle RAC, then the patch is applied. Once that occurs, the node is brought back up again. By going separately to each node, a complete shutdown is avoided, which is why the uptime for this option is consistently at or near 100%. Although some patches cannot be applied in this mode, you still have minimum downtime patching features that will still help you remain productive.
2. It is load balanced for a better performance.
With Oracle RAC, the services coordinate their sessions by registering their workload. They can also register the amount of work being handled. With this information, clients can be redirected to the least-loaded node that is running an instance for their specific services. Two types of load balancing are featured: client-side and server-side. This makes it possible to keep working at the speeds you require without the same threats of information loss.
3. It is a solution that is highly scalable.
As you grow, Oracle RAC is able to grow with you. One of its primary features is an ability for each instance to have a different configuration. That means you can put in application partitioning without a headache, have an OLTP with another instance, and manage every other instance in a way that works well with your unique setup. This all happens with just one database.
4. Unless the connections are not RAC aware, there is no need for a reconnection.
Because Oracle RAC is a node-based system, unplanned failures create a minimal impact on the user when compared to similar services. To maintain availability, clients who are connected to a failed instance are immediately established to a new connection with the surviving instances within the database. A reconnection is not necessary under most circumstances because you’re simply shifting your node presence. As long as the primary site remains intact, this benefit typically remains.
5. DML processes are able to roll back.
There are times when you’re operating in the SQL Plus environment when your data manipulation language statements don’t go as planned. Instead of having your statement become immediately permanent, this system allows you to see the effect of a DML statement in Developer. It does not become permanent until you complete a transaction which includes it. That makes it easier to roll it back, since a transaction is a sequence of SQL statements from the data based which are treated as a unit.
6. It could save you some money.
If you go with the standard edition of Oracle RAC instead of the Enterprise edition, with two nodes instead of 4, your total 3-year costs could be less than $250,000 with this system. It is important to review all configuration possibilities before committing to a specific solution to ensure you’re getting the best deal possible.
List of the Disadvantages of Oracle RAC
1. It requires a specific network configuration to work properly.
With Oracle RAC, you must have your SCAN IPs, your VIPs, and your public IP addresses all on the same public network for the database to operate properly. The private IPs must be on a different network than the public network. You must also have your private and public IPs be pingable before the installation begins. If one link in this chain is not in place, then you will develop an incorrect network configuration error.
2. You must have Oracle RAC on shared storage.
With Oracle RAC, you must have your database files, your OCR location, and your voting disk all on shared storage. If you do not, then it will not function properly. Any issue that you have with the shared disk configuration will eventually cause the system to fail, which generates an incorrect shared disk configuration error report.
3. There are a lot of prerequisites that must be completed.
When you configure the network for Oracle RAC and Clusterware, you’ll find that each node in the cluster has specific requirements that must be met. You must have at least 2 network interface cards, public interface names for every node, and the same private interface names for all nodes as well. Your network adapter must support TCP/IP and the private interface must support UDP for high-speed network adapters with a switch that supports gigabit ethernet at minimum. This is in addition to the hardware requirements and other prerequisites that must be met.
4. It is not always a cost savings solution.
If you’re thinking about Oracle RAC as a way to save money, then make sure that you’re looking at the hardware costs too. Many companies look at the software costs only, which leads them to an unpleasant surprise when it becomes time to pay the bills. A disk array with 20 TB of usable capacity for primary storage may have a 3-year cost of about $150,000 for some businesses. Add in the license fees, which can top $1 million for some users when several units are necessary, and the costs may be better if you stay local and manage your own database instead.
5. There can be some scalability limitations.
With Oracle RAC, if the application will not scale on SMP, then it will not scale either. It is also important to take a realistic approach about the latency differences you may experience with local-only memory cache instance communications and the inter-node network. This system works best when you have high performance and high availability needs. If you only have one of those needs, then a single instance server or a less complex solution may be a better option.
The advantages and disadvantages of Oracle RAC can help a business understand that they are ready for this solution or have some work that needs to be done. It has some amazing uptime statistics, provides you with protection from single instance and single server failures, and will help you take advantage of the larger SGA sizes when compared to single-instance commodity servers.
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