Exadata

Oracle Exalogic
– Is position as pre-configured Clustered Application Server

Oracle Exadata
– Is position as pre-configured Clustered Data Server
– It Support OLAP and OLTP Workload

What are the different Exadata configurations?
The Exadata Appliance configuration comes as a Full Rack, Half Rack or Quarter Rack.

The Full Rack X2-2 has
6 CPU’s per node with Intel Xeon 5670 processors
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
Total of 4 Database Server nodes.
It has 96GB of memory per database server node with a total of 7 Storage server cells

What are the key Oracle Exadata Features?
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)

What are the ways to migrate onto Exadata?
Depending on the downtime allowed there are several options:
Traditional Export/Import / DataPump
Oracle DataGuard
Tablespace transportation. / Full Transportable Export/Import
Goldengate Replication after a data restore onto Exadata.

What operating systems does Exadata support?
Exadata has traditionally run Oracle Linux OS. Recently, Solaris has also been made available on this engineered system.

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.

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?

In a traditional Oracle database, when a user selects a row or even a single column in a row,
the entire block containing that row is fetched from the disk to the buffer cache, and the
selected row (or column, as the case may be) is then extracted from the block and presented
to the user’s session. In the Exadata Database Machine
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.

Storage Indexes

How does Smart Scan achieve sending only those relevant rows and columns instead of blocks? A special data structure built on the pattern of the data within the storage cells enables this. For a specific segment, it stores the minimum, maximum, and whether nulls are present for all the columns of that segment in a specified region of the disk, usually 1MB in size. This data structure is called a storage index. When a cell gets a Smart Scan-enabled query from the database node via iDB, it checks which regions of the storage will not contain the data. For instance if the query predicate states where rating = 3, a region on the disk where the minimum and maximum values of the column RATING are 4 and 10 respectively will definitely not have any row that will match the predicate. Therefore the cell skips reading that portion of the disk. Checking the storage index, the cell excludes a lot of regions that will not contain that value and therefore saves a lot of I/O.

Although it has the word “index” in its name, a storage index is nothing like a normal index. Normal indexes are used to zero in on the locations where the rows are most likely to be found; storage indexes are used just for the opposite reason – where the rows are most likely not to be found. Also, unlike other segments, these are not stored on the disks; they reside in memory.>
How does Smart Scan achieve sending only those relevant rows and columns instead of blocks?
A special data structure built on the pattern of the data within the storage cells enables this.
For a specific segment, it stores the minimum, maximum, and whether nulls are present for all
the columns of that segment in a specified region of the disk, usually 1MB in size.
This data structure is called a storage index.
When a cell gets a Smart Scan-enabled query from the database node via iDB, it checks which
regions of the storage will not contain the data. For instance if the query predicate states
where rating = 3, a region on the disk where the minimum and maximum values of the column
RATING are 4 and 10 respectively will definitely not have any row that will match the predicate.
Therefore the cell skips reading that portion of the disk. Checking the storage index, the cell
excludes a lot of regions that will not contain that value and therefore saves a lot of I/O.

Although it has the word “index” in its name, a storage index is nothing like a normal index.
Normal indexes are used to zero in on the locations where the rows are most likely to be found;
storage indexes are used just for the opposite reason – where the rows are most likely not to
be found. Also, unlike other segments, these are not stored on the disks; they reside in memory.

Architecture

ASM mirrors and stripes disks between the appliances.
ASM failure groups are used to protect the data from disk and appliance failures.
All storage servers have processors that can execute simplified SQL and
will return the requested rows and columns.
Infiniband is used to connect the appliances to the database server.
Spare ports are available for connecting additional blades to the storage cluster.
An Enterprise Manager plugin is available for managing and monitoring the solution

Technical architecture:

The libcell library is linked in to talk to cellsrv process.
cellinit.ora decides which network takes storage traffic.
cellip.ora - list of cells, new cells can be added dynamically without shutdown
diskmon handles cell failures
cellcli is the command line interface and configuration utility
RS (Restart Server) monitors and restarts other critical processes
dcli - tool to run commands on all cells
Set cell_offload_processing parameter to TRUE
cell_offload_plan_display parameter to predict the effect of moving to Exadata.

http://www.oracle.com/technetwork/articles/oem/exadata-commands-part1-402441.html
http://www.oracle.com/technetwork/articles/oem/exadata-commands-intro-402431.html

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