International Journal of Scientific & Engineering Research Volume 2, Issue 6, June-2011 1

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Oracle Real Application Clusters

Deepali Kadam, Nandan Bhalwarkar, Rahul Neware, Rajesh Sapkale, Raunika Lamge

Abstract -This paper shows automatic failover and load balancing for Oracle real Application Clusters. rac enables you to use clustered hardware by running multiple instances against the same database. The database files are stored on disks that are either physically or logically connected to each node, so that every active instance can read from or write to them. Oracle Real Application Clusters manages data access, so that changes are coordinated between the instances and each instance sees a consistent image of the database. The Cluster Interconnect enables instances to pass coordination information and data images between each other.The architecture enables users and application to benefit from the processing power of multiple machines. Oracle RAC architecture also achieves redundancy in the case of, for example, a system crashing or becoming unavailable; the application can still access the database on any surviving instances.

Inexd Terms Oracle, real application, clusters, rac architecture, clusterware, loadbalancing, server.

1 INTRODUCTION

n the last five years, researchers have shown that com- modity clusters have the potential to provide super-
computing capabilities at a fraction of the cost of tradi- tional multiprocessor systems . At the same time, much research has been conducted in software distributed shared memory to make it as easy to program clusters as it is to program shared memory multiprocessors.
These advances in programmability and performance are making it possible to use very large clusters as a
cost-effective platform for data-intensive, long-running applications. As cluster size and application running
times increase, adding failover becomes critical.At the same time, to preserve performance scalable.
In this paper, we address the problem of designing Automatic failover system, specifically targeting scalable system. The novelty of our work lies in the combination of failover techniques with memory-mapped communi- cation, such that the resulting system can be used in very large local-area clusters. Furthermore,A common ap- proach is, Real Application Clusters manages data access, so that changes are coordinated between the instances and each instance sees a consistent image of the database. The Cluster Interconnect enables instances to pass coor- dination information and data images between each other.

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DEEPALI KADAM Btech computer engineer from

VJTI,MUMBAI,INDIA email :deepalisushpriya@gmail.com

NANDAN BHALWANKAR Btech computer engineer from

VJTI,MUMBAI,INDIA email :nandanbhalwankar123@gmail.com

RAHUL NEWARE Btech computer engineer from

VJTI,MUMBAI,INDIA email :rahulneware2007@gmail.com

RAJESH SAPKALE Btech computer engineer from

VJTI,MUMBAI,INDIA email :rajeshsapkale@hotmail.com

RAUNIKA LAMGE Btech computer engineer from

VJTI,MUMBAI,INDIA email :raunika24@gmail.com

PRAMILA CHAWAN professor computer department

VJTI,MUMBAI,INDIA email :pmchawan@vjti.org.in

BANDU MESHRAM head of computer department

VJTI,MUMBAI,INDIA email :bbmeshram@vjti.org.in
Furthermore,A common approach is, Real Application Clusters manages data access, so that changes are coordi- nated between the instances and each instance sees a con- sistent image of the database. The Cluster Interconnect enables instances to pass coordination information and data images between each other.
The architecture enables users and application to benefit from the processing power of multiple machines. RAC architecture also achieves redundancy in the case of, for example, a system crashing or becoming unavailable; the application can still access the database on any surviving instances.

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RAC ARCHITECTURE

The diagram consists of two things:
Collection of interconnected Servers, called Clusters con-
nected together using private interconnect.
The database files storing collection of database tables
which is shared among multiple instances among
servers.
A cluster consists of two or more independent, but inter-
connected, servers. Several hardware vendors have pro-
vided cluster capability over the years to meet a variety of
needs. Some clusters were intended only to provide high
availability by allowing work to be transferred to a sec-
ondary node if the active node fails. Others were de-
signed to provide scalability by allowing user connections
or work to be distributed across the nodes.
Another common feature of a cluster is that it should ap- pear to an application as if it were a single server. Similar- ly, management of several servers should be as similar to the management of a single server as possible. The cluster
management software provides this transparency. For the nodes to act as if they were a single server, files must be stored in such a way that they can be found by the specif- ic node that needs them. There are several different clus- ter topologies that address the data access issue, each de- pendent on the prim goal of the cluster designer. The in- terconnect is a physical network used as a means of communication between each node of the cluster.
A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications. Oracle Real Application Clusters
(Oracle RAC) enables you to cluster Oracle databases. Oracle RAC uses Oracle Clusterware for the infrastruc- ture to bind multiple servers so they operate as a single system.Oracle Clusterware is a portable cluster manage- ment solution that is integrated with the Oracle database. Oracle Clusterware is also a required component for us- ing Oracle RAC. In addition, Oracle Clusterware enables both single-instance Oracle databases and Oracle RAC databases to use the Oracle high-availability infrastruc- ture. Oracle Clusterware enables you to create a clustered pool of storage to be used by any combination of single- instance and Oracle RAC databases.
Oracle Real Application Clusters (RAC) is a software component you can add to a high-availability solution that enables users on multiple machines to access a single database with increased performance. RAC comprises two or more Oracle database instances running on two or more clustered machines and accessing a shared storage device via cluster technology. To support this architec- ture, the machines that host the database instances are linked by a high-speed interconnect to form the cluster. The interconnect is a physical network used as a means of communication between the nodes of the cluster. Cluster functionality is pro vided by the operating system or com-

patible third party clustering software.

Oracle RAC offers features in the following areas: Scalability
Availability
Failover
Load balancing
Oracle RAC is a cluster database with a shared cache ar- chitecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide highly scalable and available database solutions for all your business applications. Oracle RAC is a key compo- nent of Oracle's enterprise grid architecture. Oracle RAC support is included in the Oracle Database Standard Edi- tion for higher levels of system uptime.

SHARED DISK ARCHITECTURE FOR ORACLE RAC:

A shared disk file system uses a storage area net- work (SAN) or RAID array to provide direct disk access from multiple computers at the block level. Translation from file-level operations that applications use to block- level operations used by the SAN must take place on the client node. The most common type of clustered file sys- tem, a shared disk file system adds a mechanism for con- currency control which conventional file systems in- tended for local storage do not have. Clients are afforded a consistent and serializable view of the file system, avoiding corruption and unintended data loss even when multiple clients try to access the same files at the same time. Shared disk file systems also usually employ some sort of a fencing mechanism to prevent data corruption in

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case of node failures.

The underlying storage area network might use any of a number of block-level protocols, includ- ing SCSI, iSCSI, HyperSCSI, ATA over Ether- net (AoE), Fibre Channel, and InfiniBand.
There are different architectural approaches to a shared disk file system. Some distribute file information across all the servers in a cluster (fully distributed). Others util- ize a centralized metadata server. Both achieve the same result of enabling all servers to access all the data on a shared storage device

CLUSTERWARE :

Oracle Clusterware is the software, which enables the nodes to communicate with each other, and forms the cluster and makes the nodes as single logical server. Oracle Clusterware is run by Cluster Ready Services (CRS) using two key components. They are Oracle Cluster Registry (OCR), which records and maintains the cluster and node membership information. The other component is voting disk, which acts a tiebreaker during communica- tion failures. Consistent heartbeat information from all the nodes is sent to voting disk when the cluster is run- ning. CRS service has four components namely OPROCd, CRS Daemon (crsd), Oracle Cluster Synchronization Ser- vice Daemon (OCSSD) and Event Volume Manager Dae- mon (evmd) and each handles a variety of functions. Failure or death of the CRS daemon can cause the node failure and it automatically reboots the nodes to avoid the data corruption because of the possible communication failure between the nodes. The CRS daemon runs as the super user ‘root’ in the UNIX platforms and runs as a service in the windows platforms.

LOAD BALANCING :

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Clusters have become increasingly popular as powerful and cost-effective platforms for executing parallel applications In such systems, load-balancing schemes can improve system performance by attempting to assign work, at run time, to machines with idle or underutilized resources.

The Oracle RAC system can distribute the load over
many nodes this feature called as load balancing.
There are two methods of load balancing
1.Client load balancing
2.Server load balancing

Client Load Balancing distributes new connections among Oracle RAC nodes so that no one server is over- loaded with connection requests and it is configured at net service name level by providing multiple descriptions in a description list or multiple addresses in an address list. For example, if connection fails over to another node in case of failure, the client load balancing ensures that

the redirected connections are distributed among other nodes in the RAC.

Server Load Balancing distributes processing workload among Oracle RAC nodes. It divides the connection load evenly between all available listeners and distributes new user session connection requests to the least loaded lis- tener(s) based on the total number of sessions which are already connected. Each listener communicates with the other listener(s) via each database instance’s PMON process.

A farm of servers with the same function is the base of a load balancing cluster. To distribute the user requests to several nodes, a load balancer is useful. The load balancer checks the utilization of all nodes. The node with the es- timated best performance will get the next user request. This algorithm ensures the best performance available at the time is given to the users.
A very important point is the quality of the load balancer. In this case, quality means the opportunity of the system to made a highly qualified forecast about which node will offer the best performance concerning an individual ap- plication. Another aspect to make the decision is to re- connect the client to an existing session. Without any kind of protection, the load balancer could be a single point of failure.
If one node is out of service, then the whole system will still work. The load balancer will recognize the failed node, and mark the crashed system. The total perfor- mance of the load balancing cluster will be reduced, but services will still be provided.

AUTOMATIC FAILOVER:

Automatic failover is supported in database for high- safety mode. In high-safety mode with automatic failover, once the database is synchronized, if the principal server becomes unavailable, an automatic failover occurs. An automatic failover causes the secondary server to take over the role of principal server and bring its copy of the database to the user. Requiring that the server be syn- chronized prevents loss to the user during failover, be- cause every transaction committed on the principal server can also be committed on the secondary server.
Automatic failover requires the following conditions:
1. The secondary server must be running in high- safety mode
2. The secondary server must have access to the main database
How Automatic Failover Works
Under the preceding conditions, automatic failover in- itiates the following sequence of actions:
1. If the principal server fails, it changes the state of the principal server to DISCONNECTED and disconnects all clients from the principal server.
2. The secondary server register that the principal serv- er is unavailable.
3. All clients from the principal server are shifted to the secondary server by clusterware.

CONCLUSIONS:

In this paper we have shown automatic failover and load balncing for oracle real Application Clusters. an oracle rac system can protect against computer failures caused by unexpected hardware failures and operating system or server crashes, as well as processing loss caused by planned maintenance.. When node failover occurs and a service connection is redirected to another node, users can continue to access the service, unaware that it is now provided from a different node. We have also explained the architecture of oracle real application cluster,oracle clusterware,shared disk architecture.
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