1Z0-027 全真模擬試験 DEMO

問題6: Which two statements are true about the use ofi direct path loads when selecting firom
external tables in a database
on a Database Machine?
A. INSERT INTO . . . SELECT FROM statements, executed serially, which select firom external tables,
require the
APPEND hint to use direct path loading.
B. CREATE TABLE . . . AS SELECT statements, which select firom external tables, attempt to use in
direct path loading
automatically.
C. CREATE TABLE . . . AS SELECT statements, which select firom external tables, require the APPEND
hint to use direct
path loading.
D. INSERT INTO . . . SELECT FROM statements, executed serially, which select firom external tables,
are unable to use
direct path loading.
正解: A, B
Explanation:
A CTAS (Create table as select) will always use direct path (B, not C) load but IAS (Insert as select)
statement will not.
In order to achieve direct path load with an IAS statement you must add the APPEND hint to the
command (A, not D).
Direct path loads can also run in parallel. You can set the parallel degree fior a direct path load
either by adding the PARALLEL hint to the CTAS or IAS statement or by setting the
PARALLEL clause on both the external table and the table into which the data will be loaded.
Once the parallel degree has been set at CTAS will automatically do direct path load in parallel
but an IAS will not. In order to enable an IAS to do direct path load in parallel you must alter
the session to enable parallel DML.
Note:
* Parallel Direct Path Load
The key to good load perfiormance is to use direct path loads wherever possible. A direct path
load parses the input data according to the description given in the external table definition,
converts the data fior each input field to its corresponding Oracle data type, then builds a column
array structure fior the data. These column array structures are used to fiormat Oracle data blocks
and build index keys. The newly fiormatted database blocks are then written directly to the
database, bypassing the standard SQL processing engine and the database buffer cache.
Refierence: Best Practices fior Implementing a Data Warehouse on the Oracle Exadata Database
Machine; Using CTAS &
Exchange Partition Replace IAS fior Copying Partition on Exadata