database instances on serviceguard nodes

[Shivkumar]

Hi,

In a 2 node serviceguard cluster running oracle 9i; oracle has 2 identical instances running on 2 nodes and writes data to the same physical database located on shared SAN disk. This shared SAN volume is common to both the nodes.

Our DBA team refers instance on one of the node as primary instance and other node instance as secondary. Our application writes first in primary instance and then if primary is not available then writes in secondary instance. Sometime our application gives errors if primary or secondary instance (any one of them) is not available.

My question:
Oralce 9i rac and onward is using cache fusion technology which allows writing data simultaneously in both the instances of the same database. How will it impact if the application writes data in both of the instances at a time ?

Why is it necessary to refer instances as primary and secondary as both are availabel at the same time ?


Thanks,
Shiv

[Julio Yamawaki]

Hi Shiv,

Primary instance is where you create your database, including user data tablespaces.
To create a secondary, tertiary and so on, you only need to create redolog and undo, that's why it's called secondary instance.
This secondary instance will access data in primary user tablespace.

Regards,

[Shivkumar]

Appreciate more thoughts from gurus on this.

Thanks in advance.
Shiv

[Steven E. Protter · Accepted solution]

Shalom Shiv,

PSB

Oralce 9i rac and onward is using cache fusion technology which allows writing data simultaneously in both the instances of the same database.

How will it impact if the application writes data in both of the instances at a time ?

RAC is specifically designed to permit simultaneous access. There is an entire, complex mechanism to prevent database corruption. Its not possible for the same data on two machines to be changed at the same time.

RAC does provide you the ability to put more CPU power into intense operations. It still however leaves you with one copy of the database and you are just as vulnerable to I/O problems on the SAN as before.

Why is it necessary to refer instances as primary and secondary as both are availabel at the same time ?

It's not. Your DBA's are simply referring to the instances by names to keep things straight in their minds. You can call them heckle and jeckle, or mo and curly, its just primary and secondary happen to be more meaningful.

SEP

[Indira Aramandla]

Hi Shivkumar,

With OPS a primary instance is the active instance to which clients connect as with the default OPS configuration, however a secondary instance is configured to only accept client connections in the event of the primary instance failing. This avoids the extra load being passed on to the other active instances.

While the routing of transactions to specific instances is manually configurable, OPS Primary/Secondary instance feature is able to perform this operation automatically.

Real Application Clusters (RAC) is a feature in Oracle9i Database that can greatly enhance an applicationâ s scalability and availability. RAC is an Oracle database that has two or more instances accessing a shared database via cluster technology. A cluster is a group of machines (or nodes) that work together to perform the same task.

RAC architecture enables users and applications to benefit from the processing power of multiple machines. This architecture also achieves redundancy in the case of, for instance, a system crashing or becoming unavailable; the application can still access the database on any surviving instances. To support this architecture, two or more machines that host the database instances are linked by a high speed interconnect to form a cluster. The interconnect is a physical network used as a means of communication between each node of the cluster. RAC also provides system redundancy to make an application more available to provide consistent, uninterrupted service, even during failures.

Using the cache fusion technology of Oracle9i RAC, applications can achieve near linear scalability and performance. RACâ s cache fusion technology increases the size of the available working cache by uniting all the cache's in the cluster database

Cache Fusion is a new parallel database architecture for exploiting clustered computers to achieve scalability of all types of applications. Cache Fusion is a shared cache architecture that uses high speed low latency interconnects available today on clustered systems to maintain database cache coherency. Database blocks are shipped across the interconnect to the node where access to the data is needed. This is accomplished transparently to the application and users of the system.

Primary secondary instances are just terminology.



Indira A

[Indira Aramandla]

Hi Shivkumar,

With OPS a primary instance is the active instance to which clients connect as with the default OPS configuration, however a secondary instance is configured to only accept client connections in the event of the primary instance failing. This avoids the extra load being passed on to the other active instances.

While the routing of transactions to specific instances is manually configurable, OPS Primary/Secondary instance feature is able to perform this operation automatically.

Real Application Clusters (RAC) is a feature in Oracle9i Database that can greatly enhance an applicationâ s scalability and availability. RAC is an Oracle database that has two or more instances accessing a shared database via cluster technology. A cluster is a group of machines (or nodes) that work together to perform the same task.

RAC architecture enables users and applications to benefit from the processing power of multiple machines. This architecture also achieves redundancy in the case of, for instance, a system crashing or becoming unavailable; the application can still access the database on any surviving instances. To support this architecture, two or more machines that host the database instances are linked by a high speed interconnect to form a cluster. The interconnect is a physical network used as a means of communication between each node of the cluster. RAC also provides system redundancy to make an application more available to provide consistent, uninterrupted service, even during failures.

Using the cache fusion technology of Oracle9i RAC, applications can achieve near linear scalability and performance. RACâ s cache fusion technology increases the size of the available working cache by uniting all the cache's in the cluster database

Cache Fusion is a new parallel database architecture for exploiting clustered computers to achieve scalability of all types of applications. Cache Fusion is a shared cache architecture that uses high speed low latency interconnects available today on clustered systems to maintain database cache coherency. Database blocks are shipped across the interconnect to the node where access to the data is needed. This is accomplished transparently to the application and users of the system.

Primary secondary instances are just terminology.

Refer to the atached document.

Here are few Notes for references.
Available via Note 181503.1 - Real Application Clusters Whitepapers (OTN).
Cache Fusion Delivers Scalability Whitepaper
Available via Note 181503.1 - Real Application Clusters Whitepapers (OTN).

Maximum Availability Architecture Whitepaper
Available via Note 181503.1 - Real Application Clusters Whitepapers (OTN).

Oracle9i Release 2 Real Application Clusters Administration
Available via Note 188135.1 - Documentation Index for Real Application Clusters.



Indira A