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:

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.

To prepare for your Oracle DBA interview here are some additional questions focusing on other database areas.

• Oracle RAC questions
• Goldengate Interview Questions