Exam 1z0-027 topic 1 question 41 discussion

Actual exam question from Oracle's 1z0-027

Question #: 41
Topic #: 1

You are monitoring and evaluating a create index statement on your Database Machine and have run the following query after executing statement, providing the output. Shown:

Select two reasons why the statement would have produced so many "cell single block physical read" waits compared to "cell smart table scan" waits.

A. There are huge numbers of migrated rows in the table on which the index is being built.
B. There is an uncommitted transaction that has modified one block of the table on which the index is being built, in each cell.
C. There is a transaction that has modified one block of the table on which the index is being built in each cell, which committed after the create index began.
D. There are huge numbers of chained rows in the table on which the index is being built.
E. There is a ROWID column in the table on which the index is being built.

Show Suggested Answer

Suggested Answer: AD 🗳️
A: It could be that row migration.
D: It could be that row migration or chained rows could cause it.
Note:
* Some facts about scans:

Scans exists in "OLTP" systems -
Exadata smart scan requires a direct path read.
A direct path read is chosen at runtime based on internal heuristics
The STORAGE clause in an explain plan doesnt necessarily mean you will perform a smart scan.
* The buffer caching in certain "OLTP" environments can occasionally induce conventional reads when smart scan is faster.
* Typically see cell multiblock physical read instead of cell smart table scan waits
* No one-size-fits-all solution can be given here but it is very fixable.

by thuthuysphn58 at April 4, 2025, 6:39 a.m.

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