Which two statements are true about index full scans?
A.
An index fast full scan multi block I/O to read the index structure in its entirely.
B.
Index nodes are not retrieved in the index order, and there fore the nodes are not in sequence.
C.
An index fast full scan reads the index block by block.
D.
An index fast full scan reads the whole index from the lowest value to the higher value.
Explanation:
A: To speed table and index block access, Oracle uses the
db_file_multiblock_read_count parameter (which defaults to 8) to aid in getting full-table scan and
full-index scan data blocks into the data buffer cache as fast as possible.
B: The index nodes are not retrieved in index order, the rows will not be sequenced.
Note:
there are some requirements for Oracle to invoke the fast full-index scan.
Reference: index fast full scan tips
A, C – correct.
B, D – wrong.
Unlike a full scan, a fast full scan cannot eliminate a sort operation because it does not read the index in order.
https://docs.oracle.com/database/121/TGSQL/tgsql_optop.htm#TGSQL95171
I believe correct answer should be A & B
The database uses multiblock I/O to read the root block and all of the leaf and branch blocks. The databases ignores the branch and root blocks and reads the index entries on the leaf blocks
You gotta consider that FULL SCAN and FAST FULL SCAN differs in reading order.
So B – wrong
I mean that Index Full Scan reads the blocks in order.
Therefore, B – right for fast full scan, but wrong for full scans.
An index full scan reads the entire index in order. An index full scan can eliminate a separate sorting operation because the data in the index is ordered by index key.
https://docs.oracle.com/database/121/TGSQL/tgsql_optop.htm#TGSQL237
today passed this exam.
This question is wrong typed.. this must be “which two statements are true about index FAST full scans”
And in this case the right answers A and B.
Congrates bro ….
is this questions and answers were useful ?
yes, they were…
I also cleared this exam on 16-Feb. 🙂
can you please tell how mnay questions were there.
75 or 80
It seems A and B correct.
Index Full Scans
A full index scan eliminates a sort operation, because the data is ordered by the index key.
It reads the blocks singly. Oracle Database may use a full scan in any of the following situations:
Fast full index scans are an alternative to a full table scan when the index contains all the columns
that are needed for the query, and at least one column in the index key has the NOT NULL constraint.
A fast full scan accesses the data in the index itself, without accessing the table.
The database cannot use this scan to eliminate a sort operation because the data is not ordered by the index key.
The database reads the entire index using multiblock reads, unlike a full index scan, and can scan in parallel