Q) What are the differences between Oracle RAC and Oracle Grid ?
Oracle RAC Vs Oracle Grid
RAC GRID
Single system image avaiable No single system image
Proprietary interoperability with VIA No standards available
Single ownership Multiple Ownerships
Disciverable membership services Central Index and decentral information to discover
Moderate throughput Either too high or too low throughput
Guarantees capacity High capacty, varies sometimes
Most number of commodity computers Commodity and High-end computers
Centralised user management Distributed user management
Centralised resource management Distributed resource management
Central allocation and scheduling DecentraliDistributed allocation and scheduling
Q1) 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).

Q2) 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.

Q3) What is the difference between Crash recovery and Instance recovery?

When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC enviornment the same recovery for an instance is performed by the surviving nodes called Instance recovery.

Q4) 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.

Q5) How do you determine what protocol is being used for Interconnect traffic?

One of the ways is to look at the database alert log for the time period when the database was started up.

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Q6) 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.

Q7) What files components in RAC must reside on shared storage?

Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.

Q8) Where does the Clusterware write when there is a network or Storage missed heartbeat?

The network ping failure is written in $CRS_HOME/log

Q9) 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.

Q10) 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.

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