Exadata Smart Flash Caching

Smart Flash Cache:
  • 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.
  • Exadata caching mechanism focuses on caching frequently accessed data and index block with performance critical information like control file and file headers. 
  • Also we can influence caching priorities by using CELL_FLASH_CACHE storage attribute for specific database objects
What will be cached ?
  • Frequently accessed data
  • Index Block
  • File header reads and writes
  • Control file reads and writes
  • DBA can set the caching priority
What will be not cached?
  • Backup related I/O
  • Database pump I/O
  • Data file formatting
  • I/O to mirror copies
  • Table scan don't control the cache

Exadata Certification Sample Questions & Answers (1Z0-536)

I have given some sample questions for Exadata Certification. I hope it will help you to prepare for certification. 

When do you specify the type of interleaving for a grid disk?

A. When you create the cell disk

B. When you create the grid disk
C. Through ASM
D. When you create a tablespace
Answer: B

Why would you reduce the default disk_repair_time parameter?

A. To extend the availability of your ASM disk groups.

B. To reduce the need for high redundancy
C. To reduce the amount of data collected for a fast resynch
D. To increase performance of anExadata Storage Server.
Answer: C

What benefit is provided by column filtering?

A. The Exadata Storage Server can select rows based on column values listed in a SQL predicate

B. Storage indexes are built on columns for use in filtering
C. Only necessary columns are returned to the database server
D. Column filtering is a marketing term, not a real benefit
Answer: C

Which types of data are most likely to be cached In the Exadata SmartFlash Cache?

A. Results of random reads.

B. Results of table scans.
C. Write to a mirror
D. Redo data
E. All data is cached In the Flash Cache
Answer: A

What does the role attribute of a DB plan Indicate?

A. The role specified for the category

B. The role specified for the user
C. The role specified In a Data Guard environment
D. The role specified for the application
Answer: A

Your customer has designated a number of database objects to be kept persistently in the Exadata Smart Flash Cache. What happens if the total size of these objects is greater than 80% of the size of the available Exadata Smart Flash Cache?

A. Nothing

B. Exadata Smart Flash Cache expands the allocation to hold the objects.
C. Not all objects will be stored in Exadata Smart Flash Cache.
D. Overall performance is increased as more objects fit into Exadata Smart Flash Cache.
Answer: C

Which three attributes are likely to result in data being cached in the Exadata Smart Flash Cache?

A. CELL_FLASH_CACHE attribute on the data object

B. CACHE hint In the SQL statement
C. Data from a table scan
D. Small data less than 128 KBs
E. Control file I/Os
Answer: A,C,E

How many IP addresses you need to assign for each Exadata storage cell?

Cell Server Connectivity and Port Details

Following image shows back end layout of cell storage server.

Short description for each port :

ILOM -- Useful to manage the Hardware remotely

eth0 -- Use to manage the server from OS level

eth1 , eth2 & eth3 -- Not connected as there is no public network required for it.

IB0 & IB1 -- Infiniband network ports (Bonded)

KVM -- For kvm connectivity.

Database Node Connectivity and Port Details

Following image shows the back end connectivity of database server.

Short description for each port:

ILOM -- Useful to manage the Hardware remotely

eth0 -- Use to manage the server from OS level

eth1 & eth2 -- Useful for public network (Bonded)

eth3 -- This port is useful for additional network if required.

eth4 & eth5 -- 10Gig N/W port (Bonded)

IB0 & IB1 -- Infiniband network ports for storage connectivity (Bonded)

KVM -- For kvm connectivity.

How Exadata Cell Offloading Works ?

First let's know what is offloading and benefit of cell offloading in Exadata?

What is Cell Offloading :-

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.

Benefit: 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.

Below is the example of cell offloading.

We have created table cell_offload with 20 lac records.

#### Checking the cell offloading process in DB parameter  ####

SQL> show parameter cell_offload_processing

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cell_offload_processing              boolean     TRUE

# Flush buffer_cache and shared_pool to get exact result of offloading scenario #

SQL> alter system flush buffer_cache;

System altered.

SQL>  alter system flush SHARED_POOL;

System altered.

## Disabling Cell_offloading_process and checking the query result ##