Performance profiling basics in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Ruby code using Benchmark.measure

What is the output type of the following Ruby code snippet using Benchmark.measure?

Ruby

require 'benchmark'
result = Benchmark.measure do
  sum = 0
  (1..1000).each { |i| sum += i }
end
puts result.class

A Benchmark::Tms

B String

C Float

D Integer

💡 Hint

Benchmark.measure returns an object that holds timing data, not a simple number or string.

Benchmark.measure returns an instance of Benchmark::Tms which contains user, system, total, and real time data.

❓ Predict Output

intermediate

Output of Ruby code using GC.stat

What is the output type of the following Ruby code snippet?

Ruby

stats = GC.stat
puts stats.class

A Hash

B Array

C String

D Integer

💡 Hint

GC.stat returns a collection of statistics about garbage collection.

GC.stat returns a Hash containing various keys and values about the garbage collector's state.

❓ Predict Output

advanced

Output of Ruby code using Benchmark.bm

What will be printed by this Ruby code snippet?

Ruby

require 'benchmark'
Benchmark.bm do |x|
  x.report("sleep") { sleep(0.1) }
end

A A string 'sleep 0.1' printed

B An error because Benchmark.bm requires a block with arguments

C Nothing, the code runs silently

D A table with a header and one row showing label 'sleep' and times around 0.1 seconds

💡 Hint

Benchmark.bm prints a formatted table with timing results for each report block.

Benchmark.bm prints a table with a header and rows for each report label and timing data including user, system, total, and real times.

🧠 Conceptual

advanced

Identifying the cause of slow Ruby code

You run a Ruby program and notice it is slow. Which tool or method is best to find which part of the code takes the most time?

A Use puts statements to print variable values

B Use GC.start to force garbage collection

C Use Benchmark.measure blocks around suspected code sections

D Use sleep to slow down the program

💡 Hint

Profiling tools measure time spent in code sections.

Benchmark.measure helps identify which code sections take the most time by measuring execution duration.

❓ Predict Output

expert

Output of Ruby code using GC.stat keys

What is the output of this Ruby code snippet?

Ruby

stats = GC.stat
puts stats.keys.include?(:total_allocated_objects)

A Raises KeyError

B true

C nil

D false

💡 Hint

Check if :total_allocated_objects is a valid key in GC.stat hash.

:total_allocated_objects is a standard key in GC.stat hash, so keys.include? returns true.