February 4, 2019

Oracle RAC Interview Questions/FAQs Part3

Oracle RAC DBA Interview Questions Part3

41. What is HAS (High Availability Service) and the commands?
HAS includes ASM & database instance and listeners.
crsctl check has
crsctl config has
crsctl disable has
crsctl enable has
crsctl query has releaseversion
crsctl query has softwareversion
crsctl start has
crsctl stop has [-f]

42. How many nodes are supported in a RAC Database?

10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

43. What is fencing?

I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing.

44. Why Clusterware installed in root (why not in oracle)?

45. What are the wait events in RAC?


gc buffer busy
gc buffer busy acquire
gc current request 
gc cr request
gc cr failure 
gc current block lost
gc cr block lost
gc current block corrupt
gc cr block corrupt
gc current block busy
gc cr block busy
gc current block congested
gc cr block congested.
gc current block 2-way
gc cr block 2-way
gc current block 3-way
gc cr block 3-way
(even if we have n number of nodes, there can be only 3-way wait event)
gc current grant 2-way
gc cr grant 2-way
gc current grant busy
gc current grant congested
gc cr grant congested
gc cr multi block read
gc current multi block request
gc cr multi block request
gc cr block build time
gc current block flush time
gc cr block flush time
gc current block send time
gc cr block send time
gc current block pin time
gc domain validation 
gc current retry
ges inquiry response
gcs log flush sync

46. What is the difference between cr block and cur (current) block?

47. What are the initialization parameters that must have same value for every instance in an Oracle RAC database?



48. What are the new features in Oracle RAC 12c?


49. How is the Cluster Health Monitor different from OSWatcher?

50. Why we need user equivalency? What happen if we remove it between node 3,5 in a Production of 6 node RAC cluster?

51. What is the purpose of OLR?
With the OCR files being placed in ASM and accessible only when the cluster processes have started up and ASM instance is up and running. However without the OCR file the clusterware processes cannot start up.

To resolve this, a copy of the Oracle Local Registry(OLR) registry is now created on each node during the initial installation which stores node specific information and allows us to get around the problem.

Oracle Local Repository (OLR) contains information that allows the cluster processes to be started up with the OCR being in the ASM storage system. 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.

OLR stores the information on the clusterware configuration, version information, and GpnP wallets. OHASD process mostly manages this file.

52. What is difference is between relocating the SCAN using srvctl relocate scan and SCAN_LISTENER by using srvctl relocate scan_listener command?

53. 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 environment the same recovery for an instance is performed by the surviving nodes called Instance recovery.

54. Why 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.

55. 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.

56. What files components in RAC must reside on shared storage?
Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.

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