What is cache fusion?
In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary).
What is split brain?
When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split brain.
What is the interconnect used for?
It is a private network which is used to ship data blocks from one instance to another for cache fusion. The physical data blocks as well as data dictionary blocks are shared across this interconnect.
What is the purpose of OLR?
Oracle Local repository contains information that allows the cluster processes to be started up with the OCR being in the ASM storage ssytem. Since the ASM file system is unavailable until the Grid processes are started up a local copy of the contents of the OCR is required which is stored in the OLR.
What methods are available to keep the time synchronized on all nodes in the cluster?
Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
Give details on LMS
This process is called as Global Cache service process.
This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).
This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature .
What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don’t have to wait for TCP connection timeout messages.
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAC uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action .
Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.
What is a CRS resource?
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource aka cluster ready services. Some of the CRS resources are oracle RAC database, ASM instances, database services, listeners, VIP addresses, ASM diskgroups, application processes. Configuration and status of these resources that are managed by oracle clusterware is tracked by clusterware. It is interesting to note that clusterware infrastructure management is automated in the sense that the status of these resources are checked at periodic intervals, resources are restarted for fixed number of time if they fail .
How do we verify an existing current backup of OCR ?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup .
How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command:
srvctl config database -d database_name
cd CRS_HOME/bin
./crs_stat
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.
What is the difference between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.
Where does the Clusterware write when there is a network or Storage missed heartbeat?
The network ping failure is written in $CRS_HOME/log
How do you find out what OCR backups are available?
The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
If your OCR is corrupted what options do have to resolve this?
You can use either the logical or the physical OCR backup copy to restore the Repository .