Exadata

Oracle Exadata Interview Questions and Answers

What is Exadata?

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

Exadata sizing configuation

Full Rack
Half Rack
Quater Rack
1/8th Rack

What is flash cache and how it works?

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.

What are the types of EHCC?

Query Low
Query High
Archive High
Archive Low

What is the purpose of spine switch?

Spine switch is used to connect or add more Exadata machine in the cluster

What is ASR?

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.

What are the Exadata Health check tools available?

Exacheck
sundiagtest
oswatcher
OEM 12c

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 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

What are the steps to create DBFS ?

1. Create Directory
2. Create Tablespace on database which you are going to use for DBFS
3. Create user for DBFS
4. Grant required privileges to created user
5. Now connect to database with created user
6. Create dbfs filesystem by invoking dbfs_create_filesystem_advanced
7. Mount file system by starting dbfs_client

What is the difference between DBRM and IORM?

DBRM is the feature of database while IORM is the feature of storage server software.

What is smart flash cache?

Flash cache is the PCIe (Peripheral Components Interconnect Express) card which is plugged into the back end of the storage cell.

How smart scan works?

• If any query executes on database server than database server sends the extents and metadata to the storage cell.
• Smart scan will scan data blocks to identify relevant rows and columns.
• Once data identified by smart scan, it will return to database with only appropriate rows
  and columns.
• Once DB server gets the data, it will assemble returned data into result set.
• This operation will save the bandwidth as well CPUs and memory cost on database server
  as whole sql processing happens on storage server.

What are the pre-requisites to configure ASR?

Access to My Oracle Support
Internet connectivity using HTTPS
Network connectivity from ASR server to Exadata components

Which MOS ID I should refer for latest patch update?

MOS 888828.1

Which tool is used to generate initial configuration files based on customer’s data?

OEDA (Oracle Exadata Deployment Assistance)

What are the unique features of Exadata?

Smart Scan (Cell Offload)
Flash cache
EHCC (Exadata Hybrid Columnar Compression)
IORM (IO Resource Manager)
Storage Index

Which all networks available in Exadata?

Infiniband Network
ILOM and Management Network
Client/Public Network

What is client or public network in exadata?

Client or public network is used to established connectivity between database and application.

What are the steps involved for initial Exadata configuration?

• Initial network preparation
• Configure Exadata servers
• Configure Exadata software
• Configure database hosts to use Exadata
• Configure ASM and database instances
• Configure ASM disk group for Exadata

What is iDB protocol?

iDB stands for intelligent database protocol. It is a network based protocol which is responsible to
communicate between storage cell and database server.

Which processes are used by storage software?

Cellsrv – Cell Server
MS- management server
RS – Restart Server

What is LIBCELL?

Libcell stands for Library Cell which is linked with Oracle kernel. It allow oracle kernel to talk with the storage server via network based instead of operating system reads and writes.

What is checkip and what the use of it?

Checkip is the OS level script which contains IP address and hostname which will be used by Exadata in configuration phase. It checks network readiness like proper DNS configuration, it also checks there is no IP duplication in the network by pinging it which not supposed to ping initially.

Which script is used to reclaim the disk space of unused operating system?

For Linux: reclaimdisks.sh
For Solaris: reclaimdisks.pl

What should be ASM space allocation if backup performed internally?

40% storage space allocation for DATA disk group
60% storage space allocation for RECO disk group

How database server communicates to storage cell?

Database server communicates with storage cell through infiniband network.

Can I have multiple celldisk for one grid disk?

No. Celldisk can have multiple griddisk but griddisk cannot have multiple celldisk

How many FMods available on each flash card?

Four FMods (Flash Modules) are available on each flash card.

List the steps for replacing the damaged physical flash disk.

1. Identify damaged flash disk
2. Power off the cell
3. Replace flash card
4. Power on the cell
5. Verify and confirm new flash card

What is smart flash log?

Smart flash log is a temporary storage area on Exadata smart flash cache to store redoes log data.

What is smart scan offloading?

Offloading and Smart Scan are two terms that are used somewhat interchangeably. Exadata Smart
Scan offloads processing of queries from the database server to the storage server.
Processors on the Exadata Storage Server process the data on behalf of the database SQL query. Only the data requested in the query is returned to the database server.

Which parameter is used to enable and disable the smart scan?

cell_offload_processing

Can we use HCC on non-exadata environment?

No, HCC is only available data stored on Exadata storage server.

Which packaged is used by compression adviser utility?

DBMS_COMPRESSION package

What is the primary goal of storage index?

Storage indexes are a feature unique to the Exadata Database Machine whose primary goal is to reduce the amount of I/O required to service I/O requests for Exadata Smart Scan.

What is resource plan?

It is collection of plan directives that determines how database resources are to be allocated.

What is DBFS?

DBFS stands for Database File system which can be built on ASM disk group using database tablespace.

What is the purpose of infiniband spine switch?

Spine switch is used to connect multiple exadata database machines.

How to check infiniband topology?

We can verify infiniband switch topology by executing verify-topology script from one of our database server.

What is OEM?

OEM is Oracle Enterprise Manager which is centralized tool to monitor and administer systems as well software.

What is offload block filtering?

Exadata storage server filters out the blocks that are not required for the incremental backup in progress so only the blocks that are required for the backup are sent to the database.

Which command is used to monitor BCT?

SQL>select filename,status, bytes from v$block_change_tracking;

How to add memory into database server?

Power off database server
Add memory expansion into server
Power on the server

What are the major steps involved for cell server patching?

• Check and note down existing configuration of cell
• Clean up any previous patchmgr utility
• Verify that the cells meet prerequisite checks
• Patch cell server using patchmgr
• Validation updated cell

What environment is a good fit for Exadata?

Exadata was originally designed for the warehouse environment. Later it was enhanced for use in the OLTP databases as well.

What are the advantages of Exadata?

The Exadata cluster allows for consistent performance while allowing for increased throughput. As load increases on the cluster the performance remains consistent by utilizing inter-instance and intra-instance parallelism.

It should not be expected that just moving to Exadata will improve performance. In most cases it will especially if the current database host is overloaded.

What is the secret behind Exadata’s higher throughput?

Exadata ships less data through the pipes between the storage and the database nodes and other nodes in the RAC cluster.

Also it’s ability to do massive parallelism by running parallel processes across all the nodes in the cluster provides it much higher level of throughput.

It also has much bigger pipes in the cluster using Infiniband interconnect for inter-instance data block transfers as high as 5X of fiberchannel networks.

What are the different Exadata configurations?

The Exadata Appliance configuration comes as a Full Rack, Half Rack, Quarter Rack or 1/8th rack.

The Full Rack X2-2 has 6 CPU’s per node with Intel Xeon 5670 processors and a total of 8 Database Server nodes. These servers have 96GB of memory on each node. A total of 14 Storage server cells communicate with the storage and push the requested data from the storage to the compute nodes.

The Half Rack has exactly half the capacity. It has 6 CPU’s per node with core Intel Xeon 5670 processors and a total of 4 Database Server nodes. It has 96GB of memory per database server node with a total of 7 Storage server cells.

The Exadata is also available in the 1/8th Rack configuration.

What are the key Hardware components?

• DB Server
• Storage Server Cells
• High Speed Infiniband Switch
• Cisco Switch

What are the Key Software Features?

• Smart Scan,
• Smart Flash Cache
• Storage Index
• Exadata Hybrid Columnar Compression (EHCC)
• IORM (I/O Resource Manager)

What is a Cell and Grid Disk?

Cell and Grid Disk are a logical component of the physical Exadata storage. A cell or Exadata Storage server cell is a combination of Disk Drives put together to store user data. Each Cell Disk corresponds to a LUN (Logical Unit) which has been formatted by the Exadata Storage Server Software. Typically, each cell has 12 disk drives mapped to it.

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.

What is IORM?

IORM stands for I/O Resource Manager.

It manages the I/O demand based on the configuration, with the amount of resources available. It ensures that none of the I/O cells become oversubscribed with the I/O requests. This is achieved by managing the incoming requests at a consumer group level.

Using IORM, you can divide the I/O bandwidth between multiple databases.

To implement IORM resource groups, consumers and plans need to be created first.

What is hybrid columnar compression?

Hybrid Columnar compression, also called HCC, is a feature of Exadata which is used for compressing data at column level for a table.

It creates compression data units which consist of logical grouping of columns values typically having several data blocks in it. Each data block has data from columns for multiple rows.

This logarithm has the potential to reduce the storage used by the data and reduce disk I/O enhancing performance for the queries.

The different types of HCC compression include:

Query Low

Query High

Archive High

Archive Low

What is Flash cache?

Four 96G PCIe flash memory cards are present on each Exadata Storage Server cell which provide very fast access to the data stored on it.

This is further achieved by also provides mechanism to reduces data access latency by retrieving data from memory rather than having to access data from disk. A total flash storage of 384GB per cell is available on the Exadata appliance.

What is Smart Scan?

It is a feature of the Exadata Software which enhances the database performance many times over. It processes queries in an intelligent way, retrieving specific rows rather than the complete blocks.

It applies filtering criteria at the storage level based on the selection criteria specified in the query.

It also performs column projection which is a process of sending only required columns for the query back to the database host/instance.

What are the Parallelism instance parameter used in Exadata?

The parameter PARALLEL_FORCE_LOCAL can be specified at the session level for a particular job.

How do you Test performance of Exadata?

You can use the “calibrate” commands at the cellcli command line.

What are the ways to migrate onto Exadata?

Depending on the downtime allowed there are several options:

• Oracle DataGuard
• Traditional Export/Import
• Tablespace transportation
• Goldengate Replication after a data restore onto Exadata.

What types of operations does Exadata “offload”?

Some of the operations that are offloaded from the database host to the cell servers are:

• Predicate filtering
• Column project filtering
• Join processing
• Backups

What is cellcli?

This is the command line utility used to managed the cell storage.

How do you create obtain info on the Celldisks?

At the cellcli command line you can issue the “list celldisk” command.

How would you create a grid disk?

At the cellcli command you would need to issue the “create grididsk all ..” command.

What are the cellinit.ora and the cellip.ora files used for?

These files have the hostnames and the ip address of all the nodes in the cluster. They are used to run commands on remote database and cellserver nodes from a local host.

Example:
cat /etc/oracle/cell/network-config/cellinit.ora
ipaddress1=192.168.47.21/24

$ cat /etc/oracle/cell/network-config/cellip.ora
cell=”192.168.47.21:5042″
cell=”192.168.47.22:5042″
cell=”192.168.47.23:5042″

What operating systems does Exadata support?

Exadata has traditionally run Oracle Linux OS. Recently, Solaris has also been made available on this engineered system.