Redis Certified Developer: Exam Practice Tests by Scutaru Cristian

Author:Scutaru, Cristian [Scutaru, Cristian]
Language: eng
Format: epub
Published: 2020-08-20T16:00:00+00:00

Practice Test 2 - Answers and Explanations

Question 1:

What is the most effective way to get the number of keys in a database? (select one)

A) INFO KEYSPACE

B) KEYS

C) DBSIZE

D) KEYCOUNT

Answer: C

Domain: Performance

Explanation:

DBSIZE is specifically designed to return the number of keys in the currently-selected database, in O(1) time. INFO KEYSPACE is also fast and returns this information, but is not the most efficient way here, as it displays other data as well.

KEYS is an overkill way to return all keys from a database, a command to be generally avoided. And there is no KEYCOUNT command in Redis.

You'll be frequently asked about performance issues on the total number of keys, or set members.

References:

https://redis.io/commands/dbsize

https://redis.io/commands/info

Question 2:

What Redis command can remove a field-value pair from a stream entry? (select one)

A) XDEL

B) XREM

C) XTRIM

D) There is no such command.

Answer: D

Domain: Data Structures

Explanation:

Streams are read-only and append-only collections of map-like entries. So you cannot modify or remove anything from the field-value pairs of an entry.

XDEL removes entries from the stream, while XTRIM can reduce the stream to a certain size. HDEL can remove field-value pairs, but from hashes.

There is no XREM command. There are SREM and ZREM to remove members from sets and sorted sets.

Important to remember stream entries are read-only, cannot be modified.

References:

https://redis.io/topics/streams-intro

Question 3:

Which is NOT a value that can be returned by TYPE? (select one)

A) nil

B) hash

C) none

D) string

Answer: A

Domain: Data Structures

Explanation:

TYPE can return one of the following values: string, list, set, zset, hash or stream. Also, it returns none (not nil) for the key not found.

References:

https://redis.io/commands/type

Question 4:

You have a myzset sorted set with { a, b, c, d, e, f, g } members, all with the same score.

What command can return the { f, e, d, c, b } members, in this exact order? (select one)

A)

ZREVRANGE myzset (g [aaa

B)

ZREVRANGEBYLEX myzset [g [a

C)

ZRANGEBYLEX myzset (g [aaa

D)

ZREVRANGEBYLEX myzset (g [aaa

Answer: D

Domain: Data Structures

Explanation:

The lexicographic range here could be from (a to (g, or even [aaa to (g (because aaa comes after a). A reverse order would rather specify from (g to [aaa.

First call will fail, because ZREVRANGE (like ZRANGE) must take index positions as integer arguments, not regex patter expressions.

Second call looks good, except a is also included in the result. Corrected similar version is the last call.

Third call is similar to the correct answer, but it returns { b, c, d, e, f } without reversing the order.

Get familiar with the ZRANGE, ZRANGEBYLEX and ZRANGEBYSCORE commands. Also with their reverse forms ZREVRANGE, ZREVRANGEBYLEX and ZREVRANGEBYSCORE.

References:

https://redis.io/commands/zrevrangebylex

Question 5:

What patterns can you implement with RPOPLPUSH? (check all that apply)

A) circular list

B) blocking stack

C) blocking queue

D) reliable queue

Answer: A, D

Domain: Data Modeling

Explanation:

Reliable queue and circular list patterns are described in the referenced article.

References:

https://redis.io/commands/rpoplpush

Question 6:

What is the meaning of this text sent to the server through the RESP protocol? (select one)

"*3\r\n$3\r\nfoo\r\n+OK\r\n:1\r\n"

A) A command with code 3 and "foo", "OK", 1 arguments.

B) A ["foo", "OK", 1] array.

C) A ["foo", "OK", "1"] array.

D) This is an invalid string for the RESP protocol.

Answer: B

Domain: Debugging

Explanation:

RESP (REdis Serialization Protocol) is a text-based simple protocol Redis sends back and forth commands.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.