Oracle Exadata Database Interview Questions and Answers

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

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

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.

• The Exadata Appliance configuration comes as a Full Rack, Half Rack or Quarter Rack.
• The Full Rack X2-2 has 6 CPUs per node with Intel Xeon 5670 processors and a total of 8 Database Server nodes, also known as compute 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 CPUs 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

Some of the key hardware and software features are:

Hardware level

• Storage Server Cells.
• High Speed Infiniband Switch.

Software level

• Smart Scan.
• Flash Cache.
• Hybrid Columnar Compression.
• IORM (I/O Resource Manager).

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.

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.

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.

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 reduces data acess 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.

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

Depending on the downtime allowed there are several options:

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

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.

• 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.

SNMP: Simple Network Management Protocol

• KEEP
• DEFAULT
• NONE

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.

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

• Database Instance
• ASM Instance
• Database Resource Manager

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.

There are 53 wait events are exadata specific events.

+DBFS_DG

Cell flash cache read hits

• Golden Gate
• Transportable Tablespace
• Incremental Transportable Tablespace
• Data Pump

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

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.

Before and after any configuration change in Database Machine

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).

40 Gbps

writethrough –> Falshcache will be used only for reading purpose.

writeback –> Flashcache will be used for both reading and writing.

SQL>alter table table_name move compress for query high;

IORM stand for I/O Resource Manager which manages the I/Os of multiple database on storage cell.

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.

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.

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

• Query Low
• Query High
• Archive High
• Archive Low

• Exacheck
• sundiagtest
• oswatcher
• OEM 12c

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.

Database servers has two options for OS either Linux or Solaris which can be finalized at the time of configuration.

Cell storage comes with Linux only.

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

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.