Oracle RAC Flashcards
rac master
Can we manually force a particular scan ip (out of the three) to relocate on a particular host
srvctl relocate scan_LISTENER -i 1 -n node1 $ srvctl relocate scan -h Usage: srvctl relocate scan -i [-n ] -i Ordinal number of IP address -n SCAN VIP node name -h Print usage
Does scan actually performs connection load balancing?
Yes, it does. The LREG process of each instance registers the database service with the local listener as well as all the SCAN listeners (typically they are specified by the parameter: REMOTE_LISTENER). When a connection request gets routed to a particular SCAN listener, then the SCAN listener does a quick calculation to find out the least loaded node, and once it gets that information, it sends the address of the local listener on that node back to the client to establish the connection. That is how load balancing is done by the SCAN listeners.
For clients connecting using SCAN, three IP addresses will be received by the client by resolving the SCAN name through DNS as discussed. The client will then go through the list it receives from the DNS and try connecting through one of the IPs received. If the client receives an error, it will try the other addresses before returning an error to the user or application. This is similar to how client connection failover works in previous releases when an address list is provided in the client connection string.
When a SCAN Listener receives a connection request, the SCAN Listener will check for the least loaded instance providing the requested service. It will then re-direct the connection request to the local listener on the node where the least loaded instance is running. Subsequently, the client will
be given the address of the local listener. The local listener will finally create the connection to the database instance.
Is having odd number of Scan listener a recommended practice?
No, it’s not a recommended practice. The only thing Oracle recommends is that the SCAN resolves to three VIP addresses, to provide high availability and scalability . If the SCAN resolves to three addresses, then three SCAN VIPs and three SCAN listeners are created. Each SCAN listener depends on its corresponding SCAN VIP. The SCAN listeners cannot start until the SCAN VIP is available on a node.
Difference between static and dynamic listener registration
1) the relevant one is that - if you want to remotely startup the database, you need to have a statically registered connect string, otherwise - since the database isn’t up - it wouldn’t be registered.
2) use dynamic registration for all application connects - all of them. Use static only if and when you need to remotely start the database over the network.
What is cache fusion?
Oracle RAC Cache Fusion is simply where Oracle RAC transfers data blocks from the buffer cache of one instance to the buffer cache of another instance across the cluster interconnect. Transfers across this private network are in order of magnitude better than disk I/O activity and they help Oracle RAC performance
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.
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) c
ow do you find out what OCR backups are available?
The ocrconfig -showbackup
What is a VIP in RAC use for?
The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
How do we know which database instances are part of a RAC cluster
You can query the V$ACTIVE_INSTANCES
How do you backup ASM Metadata?
ou can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
What files can be stored in the ASM diskgroup?
n 11g the following files can be stored in ASM diskgroups.
Datafiles
Redo logfiles
Spfiles
In 12c the files below can also new be stored in the ASM Diskgroup
Password file
What are some of the RAC specific parameters?
Some of the RAC parameters are: CLUSTER_DATABASE CLUSTER_DATABASE_INSTANCE INSTANCE_TYPE (RDBMS or ASM) ACTIVE_INSTANCE_COUNT UNDO_MANAGEMENT
what is oracle GNS -
GNS provides dynamic DHCP allocated addresses for the SCAN and nodes VIPs
delete and Add Node is simplified compared to using static addresses
FLEX ASM
With Oracle Flex ASM, the clients can connect to remote ASM using network connection (ie ASM network ).
