Top 30 RAC Interview
Questions That Helped Me.
------------------------------------------------------------------------------------------
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 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.
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.
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.
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.
What files components in
RAC must reside on shared storage?
Spfiles, ControlFiles, Datafiles and Redolog files should be
created on shared storage.
Where does the Clusterware
write when there is a network or Storage missed heartbeat?
The network ping failure is written in $CRS_HOME/log
How do you find out what
OCR backups are available?
The ocrconfig -showbackup can be run to find out the automatic
and manually run backups.
If your OCR is corrupted
what options do have to resolve this?
You can use either the logical or the physical OCR backup copy
to restore the Repository.
How do you find out what
object has its blocks being shipped across the instance the most?
You can use the dba_hist_seg_stats.
What is a VIP in RAC use
for?
The VIP is an alternate Virtual IP address assigned to each node
in a cluster. During a node failure the VIP of the failed node moves to the
surviving node and relays to the application that the node has gone down.
Without VIP, the application will wait for TCP timeout and then find out that
the session is no longer live due to the failure.
How do we know which
database instances are part of a RAC cluster?
You can query the V$ACTIVE_INSTANCES view to determine the
member instances of the RAC cluster.
What is OCLUMON used for
in a cluster environment?
The Cluster Health Monitor (CHM) stores operating system metrics
in the CHM repository for all nodes in a RAC cluster. It stores information on
CPU, memory, process, network and other OS data, This information can later be
retrieved and used to troubleshoot and identify any cluster related issues. It
is a default component of the 11gr2 grid install. The data is stored in the
master repository and replicated to a standby repository on a different node.
What would be the possible
performance impact in a cluster if a less powerful node (e.g. slower CPU’s) is
added to the cluster?
All processing will show down to the CPU speed of the slowest
server.
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 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.
What is the default memory
allocation for ASM?
In 10g the default SGA size is 1G in 11g it is set to 256M and
in 12c ASM it is set back to 1G.
How do you backup ASM
Metadata?
You 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?
In 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 it the ASM
POWER_LIMIT?
This is the parameter which controls the number of Allocation
units the ASM instance will try to rebalance at any given time. In ASM versions
less than 11.2.0.3 the default value is 11 however it has been changed to
unlimited in later versions.
What is a rolling upgrade?
A patch is considered a rolling if it is can be applied to the
cluster binaries without having to shutting down the database in a RAC
environment. All nodes in the cluster are patched in a rolling manner, one by
one, with only the node which is being patched unavailable while all other
instance open.
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 the future of the
Oracle Grid?
The Grid software is becoming more and more capable of not just
supporting HA for Oracle Databases but also other applications including
Oracle’s applications. With 12c there are more features and functionality
built-in and it is easier to deploy these pre-built solutions, available for
common Oracle applications.
What components of the
Grid should I back up?
Is there an easy way to
verify the inventory for all remote nodes
You can run the opatch lsinventory
-all_nodes command from a single node to
look at the inventory details for all nodes in the cluster.
Additional Oracle
Questions?
If you have additional Oracle questions, feel free to comment
and let us know. We will answer you questions here or in another blog.
---------------All of the blogs are for my own reference only---------------------
No comments:
Post a Comment