Oracle Oracle Certifications 1Z0-874 Questions & Answers

• Question 131:

  Consider the following: mysql> EXPLAIN SELECT Name FROM Country WHERE Code = 'CAN'\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: Country type: const possible_keys: PRIMARY key: PRIMARY key_len: 3 ref: const rows: 1

  Extra:

  Which of the following best describes the meaning of the value of the type column?

  A. The table has exactly one row.

  B. Several rows may be read from the table.

  C. Only one row of all its rows need to be read.

  Correct Answer: C

• Question 132:

  Which of the following best describes why InnoDB tables should always have primary keys and why they should be short?

  A. Because InnoDB uses primary keys to locate tables, and shorter keys make quicker lookups.

  B. Because InnoDB uses primary keys to locate table rows, and shorter keys make quicker lookups.

  C. Because InnoDB stores pointers in a log to all the primary keys and shorter keys make this log smaller.

  Correct Answer: B

• Question 133:

  Which of the following best describes how the relay log works?

  A. It records the times when the slave connects to the master.

  B. When a slave receives a change from the master, it is recorded in the relay log first and processed later.

  C. When a slave receives a change from the master, it is processed first and then recorded in the relay log.

  Correct Answer: B

• Question 134:

  With replication, what on the master is used to send commands to the slave?

  A. The relay log.

  B. The binary log.

  C. The SQL Thread.

  Correct Answer: B

• Question 135:

  Given the following MyISAM table structure:

  mysql> desc city;

  +-------------+----------+------+-----+---------+----------------+

  | Field | Type | Null | Key | Default | Extra |

  +-------------+----------+------+-----+---------+----------------+

  | ID | int(11) | | PRI | NULL | auto_increment |

  | Name | char(35) | | | | |

  | CountryCode | char(3) | | | | |

  | District | char(20) | | | | |

  | Population | int(11) | | MUL | 0 | |

  +-------------+----------+------+-----+---------+----------------+

  and the following SQL statement:

  SELECT Population

  FROM city

  WHERE Population = 10000

  ORDER BY Population

  LIMIT 5;

  Which of the following statements best describes how MySQL optimizer executes the query?

  A. The optimizer uses the primary key column ID to read the index values, then uses the index on Population to filter the results. The optimizer will always choose to use a unique index first, then use a secondary index if available.

  B. The optimizer uses the index on the Population column to search and filter the WHERE clause. A temporary table is used to perform a filesort on the results, and then only 5 records are returned to the client.

  C. The optimizer uses the index on the Population column to search, filter and sort the Population column, then returns 5 records to the client. The optimizer does not need to read the data rows, and can return values from the index only, because the index contains just integer values that form a leftmost prefix for the key.

  D. The optimizer uses the index on the Population column to search, filter and sort the Population column, and returns 5 records to the client. The optimizer does not need to read the data rows, and can return values from the index only because only those columns where specified in the SELECT statement.

  E. The optimizer will never read data from disk, since MySQL caches both data and index in the key buffer.

  Correct Answer: D

• Question 136:

  Which of the following statements are required to create a key cache of 4 MB, assign the MyISAM table world. City to it and preload the index?

  A. mysql> SET GLOBAL city_cache.key_buffer_size = 4194304;mysql> CACHE INDEX world.City IN city_cache;mysql> LOAD INDEX INTO CACHE world.City;

  B. mysql> ALTER TABLE world.city KEY_CACHE = 4194304;

  C. mysql> CREATE CACHE FOR world.City SIZE = 4194304;

  D. It is not possible to create a key cache for a specific MyISAM table, only the global key cache can be used.

  Correct Answer: A

• Question 137:

  How can the SHOW PROCESSLIST command be helpful when optimizing queries?

  A. It shows if a query is using an index or not.

  B. It shows how the server processes a query.

  C. If checked periodically, it can reveal queries that cause other queries to hang.

  D. It shows the percentage of processing power that each query is using on a server.

  Correct Answer: C

• Question 138:

  Which of the following best describes what the master.info file contains and how it is used?

  A. It contains the values from the CHANGE MASTER statement.

  B. When the slave restarts it looks for which master to use from this file.

  C. It contains information about the master server, its slaves and its configuration.

  D. It is used by an administrator to determine what slaves connect to the master, and other information about the master server.

  Correct Answer: D