Exadata Interview Questions


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Based on our experience as an interviewer and interviewee, here we have consolidated some of the generic Exadata interview questions and answers.

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Exadata is pre-configured combination of hardware and software which provides a platform to run the Oracle Database. 

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  • Key components of Exadata
DB Server
Cell Storage
Infiniband Switch
Cisco Switch
PDU
Smart Scan
Smart Flash Cache
IORM 
Storage Index
EHCC (Exadata Hybrid Columnar Compression)


  • Exadata Sizing
Exadata comes in follwing configuration

Full Rack
Half Rack
Quater Rack
1/8th Rack

Storage Indexes consist of a minimum and a maximum value for up to eight columns. This structure is maintained for 1MB chunks of storage (storage regions). 

Storage Indexes are stored in memory only and are never written to disk.
Storage Index filter out data from the consideration.

  • Which protocol used by ASR to send notification? 
SNMP

  • Is manually intervance possible in storage index?
No
  • What are the options to update cell_flashcache for any object?
KEEP
DEFAULT
NONE

  • What is the default size of smart flash log?
512MB per module.

Each storage cell having 4 modules so its 4X512 MB per CELL

The flash cache is a hardware component configured in the exadata storage cell server which delivers high performance in read and write operations.

Primary task of smart flash cache is to hold frequently accessed data in flash cache so next time if same data required than physical read can be avoided by reading the data from flash cache.

cellcli - It is cell command line utility. We can manage cell storage with the use of cellcli utility. We can say it's utility to administer cell storage.

cellcli-alter cellcli-create cellcli-drop cellcli-list 

  • Types of EHCC:
Query Low
Query High
Archive High
Archive Low

  • Which package can be used to estimate the compression ration of table?
DBMS_COMPRESSION

MS- Management Server
cellsrv - Cell Server
RS - Restart Server

  • How to replace faulty HDD in Exadata Storage?
All the HDD are hot swapable so if we are using proper redundacny than we can direct remove and replace new HDD.

Storage software will take care all the stuffs in background after replacing the HDD.

  • How many disk comes with in a storage cell?
12

  • What is the purpose of spine switch?
Spine switch is used to connect or add more Exadata machine in the cluster

  • How to migrate database from normal setup to Exadata ?
There many methods we can use to migrate DB to Exadata. Below are some of them.

Export/Import
Physical Standby
Logical Standby
Transportable Tablespace
Transportable Database
Golden gate
RMAN cold and hot backup restoration
Oracle Streams

Use of migration method is totally depends on source setup as well as downtime consideration.

Shutdown Procedure:

Stop Database and Listener
Stop Cluster
Shutdown Database Servers
Shutdown Cell Storage
Shutdown all the switches
Remove powers from PDUs

Start-up procedure would be in reverse order.

  • How many database servers comes in 1/8th rack and quarter rack?
2

  • How many cell storage comes in full rack exadata machine?
14

  • Can we use flash disk as ASM disk?
Yes

  • Which protocol used for communication between database server and storage server?
iDB protocol

  • Which OS is supports in Exadata?
Database servers has two option for OS either Linux or Solaris which can be finalized at the time of configuration

Cell storage comes with Linux only.

ASR is the tool to manage the Oracle hardware. Full form of ASR is Auto Service Request.

Whenever any hardware fault occurs ASR automatically raise SR in Oracle Support and send notification to respective customer.

  • How to integrate Exadata with OEM 12c?
-Install OEM agent on DB server
-Launch auto discovery with the use of One Command XML file
-Specify required credentials for all the components
-Review Configuration
-Complete the setup

  • How to upgrade firmware of Exadata components?
It can be done through ILOM of DB or Cell server.

  • Where we can define which cell storage can be used by particular database server?
CELLIP.ORA file contains the list of storage server which is accessed by DB server.

  • What are the Exadata Health check tools?
Exacheck
sundiagtest
oswatcher
OEM 12c

  • What is EHCC?
EHCC is Exadata Hybrid Columnar Compression which is used to compress data in the Database.

It refers to the fact that part of the traditional SQL processing done by the database can be “offloaded” from the database layer to the storage layer

The primary benefit of Offloading is the reduction in the volume of data that must be returned to the database server. This is one of the major bottlenecks of most  large databases.

  • What is the difference between cellcli and dcli?
Cellcli can be used on respective cell storage only.
DCLi (Distributed command Line Utility) - DCLI can be used to replicate command on multipla storage as well as DB servers.

  • What is IORM and what is its role in Exadata?
IORM stand for I/O Resource Manager which manages the I/Os of multiple database on storage cell.

  • How we can check whether oracle best practice has been configured on Exadata?
We can execute Exacheck and verify the best practice setup on Exadata machine.

  • How many networks required in Exadata?
Public/Client Network --- For Application Connectivity
Management Network --- For Exadata H/W management
Private Network -- For cluster inter connectivity and Storage connectivity

  • What is the command to enable query high compression on table?
SQL>alter table table_name move compress for query high;

  • How to take cell storage software backup?
It is not required to take a backup as it happens automatically.
Exadata use internal USB drive called the Cellboot Flash Drive to take backup of software.

  • What is the difference between wright-through and write-back flashcache mode?
writethrough --> Falshcache will be used only for reading purpose
writeback --> Flashcache will be used for both reading and writing

  • Which feature of Exadata is used to eliminate disk IO?
Flash Cache

  • What is the capacity of Infiniband port?
40 Gbps

  • What is the difference between high capacity and high performance disk?
High capacity disk comes with more storage space and less rpm (7.5k)
High Performance disk comes with less storage and high rpm (15k)

  • When one should execute Exacheck?
Before and after any configuration change in Database Machine

  • What is grid disk?
Grid Disks are created on top of Cell Disks and are presented to Oracle ASM as ASM disks. 
Space is allocated in chunks from the outer tracks of the Cell disk and moving inwards. One can have multiple Grid Disks per Cell disk.

  • Which network is used for RAC inter-connectivity?
Infiniband Network
-Create Directory
-Create Tablespace on database which you are going to use for DBFS
-Create user for DBFS
-Grant required privileges to created user
-Now connect to database with created user
-Create dbfs filesystem by invoking dbfs_create_filesystem_advanced
-Mount file system by starting dbfs_client

  • Which migration methodology available if want to migrate from high endian to low endian OS architecture?
1. Golden Gate
2. Transportable Tablespace
3. Incremental Transportable Tablespace
4. Data Pump

  • How much time required to apply bundle patch on Half rack Exadata Database Machine with rolling option?
Approximate 3 hours per Cell and DB server including Infiniband & PDU patching required 1 hour each

  • What benefit we can get if we apply bundle patch on exadata in rolling fashion while ASM configured with high redundancy?
It will reduce the risk of storage disk failure 


  • Advantages and disadvantages of rolling and non-rolling patching on Exadata Database Machine.
Rolling

Advantages

No downtime required

Disadvantages

It takes more time to apply bundle patches
If ASM is on normal redundancy than disk failure on another Cell could lead to the DB corruption.

Non-Rolling

Advantages

Less time required to do the patching
It could eliminate the risk of single disk failure if ASM configured with normal redundancy

Disadvantages

Downtime required while applying bundle patch.

  • Which ASM parameters are responsible for Auto disk management in Exadata?
_AUTO_MANAGE_MAX_ONLINE_TRIES --- It controls maximum number of                                                                   attempts to make disk Online
_AUTO_MANAGE_EXADATA_DISKS --- It control auto disk management feature
_AUTO_MANAGE_NUM_TRIES    --- It controls maximum number of                                                             attempt to perform an automatic operation

  • How to enable Flashcache compression?
CellCLI> ALTER CELL flashCacheCompress=true

  • Which statistic can be used to check flash hit ration on database level?
Cell flash cache read hits


  • Which disk group is used to keep OCR files on Exadata?
+DBFS_DG


  • How many Exadata wait events contained in 11.2.0.3 release?
There are 53 wait events are exadata specific events.

  • What is the difference between an Exadata X3-2 machine and an Exadata X3-8 machine?
The X3-8 is comprised of 2 large SMP compute servers while the X3-2 can scale to as many as 8 compute servers as processing requirements increase. 


  • What are the three major components of Exadata database server?
Database Instance
ASM Instance
Database Resource Manager

  • What is the difference between DBRM and IORM?
DBRM is the feature of database while IORM is the feature of storage server software.


  • How many Exadata Storage Server Nodes are included in Exadata Database Machine X4-8?
14 storage nodes


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