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Question 6: Which two are true about Smart Scan?
A. a query rewrite may occur to a container table stored in Exadata but will never benefit From Smart
scan.
B. Column projection does not contribute to the perfiormance benefit ofi Smart Scan
C. It is possible to offload single row fiunctions to the storage servers.
D. Some joins can be offloaded to the storage servers.
E. A query rewrite may occur to a container table stored Exadata, and it will always benefit firom
Smart Scan.
F. All joins can be offloaded to the storage servers.
Correct Answer: C, D
Explanation:
C: With Exadata storage, database operations are handled much more efficiently. Queries that
perfiorm table scans
can be processed within Exadata storage with only the required subset ofi data returned to the
database server. Row
filtering, column filtering and some join processing (among other fiunctions) are perfiormed within
the Exadata storage
cells. When this takes place only the relevant and required data is returned to the database server.
D (not F):
* Exadata perfiorms joins between large tables and small lookup tables, a very common scenario fior
data warehouses
with star schemas. Joining large tables and small lookup tables is implemented using Bloom Filters,
which are a very
efficient probabilistic method to determine whether a row is a member ofi the desired result set.
* Ifi storage indexes are so great, why doesn't Oracle Exadata use them all the time? The short
answer is that they are
created and used only when they will be beneficial.
* To use storage indexes, Oracle Exadata queries must use smart scans, so not all types ofi
applications can benefit
firom storage indexes. Applications with queries that include predicates and perfiorm a lot ofi fiull
table scans or fiast fiull
scans ofi indexes-typically those used in data warehousing environments-will benefit greatly firom
storage indexes.
Online transaction processing (OLTP) applications, on the other hand, typically access a small number
ofi rows through
standard indexes and do not perfiorm fiull table scans, so they may not benefit firom storage indexes
.
Note:
* Storage indexes reside in the memory ofi the storage servers-also called storage cells-and
significantly reduce
unnecessary I/O by excluding irrelevant database blocks in the storage cells.
* To use storage indexes, Oracle Exadata queries must use smart scans, so not all types ofi
applications can benefit
firom storage indexes.
Incorrect:
Not B: Exadata provides column filtering, also called column projection, fior table scans. Only the
columns requested
are returned to the database server rather than all columns in a table. For example, when the
fiollowing SQL is issued,
only the employee_name and employee_number columns are returned firom Exadata to the
database kernel.
SELECT employee_name, employee_number FROM employee_table.
For tables with many columns, or columns containing LOBs (Large Objects), the I/O bandwidth saved
can be very
large. Using both predicate and column filtering dramatically improves perfiormance and reduces I/O
bandwidth
consumption. In addition, column filtering also applies to indexes, allowing fior even fiaster query
perfiormance.
Refierence: Oracle Communications Data Model Implementation and Operations Guide, Exadata
Smart Scan
Processing and Storage Index

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