class ScoutApm::CallSet

Encapsulates our logic to determine when a backtrace should be collected.

Constants

N_PLUS_ONE_MAGIC_NUMBER
N_PLUS_ONE_TIME_THRESHOLD

Attributes

call_count[R]

Public Class Methods

new() click to toggle source
# File lib/scout_apm/call_set.rb, line 10
def initialize
  @items = [] # An array of Layer descriptions that are associated w/a single Layer name (ex: User/find). Note this may contain nil items.
  @grouped_items = Hash.new { |h, k| h[k] = [] } # items groups by their normalized name since multiple layers could have the same layer name.
  @call_count = 0
  @captured = false # cached for performance
  @start_time = Time.now
  @past_start_time = false # cached for performance
end

Public Instance Methods

at_magic_number?() click to toggle source
# File lib/scout_apm/call_set.rb, line 45
def at_magic_number?
  grouped_items[unique_name_for(@items.last)].size >= N_PLUS_ONE_MAGIC_NUMBER
end
capture_backtrace?() click to toggle source

We're selective on capturing a backtrace for two reasons:

  • Grouping ActiveRecord calls requires us to sanitize the SQL. This isn't cheap.

  • Capturing backtraces isn't cheap.

# File lib/scout_apm/call_set.rb, line 39
def capture_backtrace?
  if !@captured && @call_count >= N_PLUS_ONE_MAGIC_NUMBER && past_time_threshold? && at_magic_number?
    @captured = true
  end
end
grouped_items() click to toggle source
# File lib/scout_apm/call_set.rb, line 49
def grouped_items
  if @grouped_items.any? 
    @grouped_items
  else
    @grouped_items.merge!(@items.group_by { |item| unique_name_for(item) })
  end
end
past_time_threshold?() click to toggle source

Limit our workload if time across this set of calls is small.

# File lib/scout_apm/call_set.rb, line 31
def past_time_threshold?
  return true if @past_time_threshold # no need to check again once past
  @past_time_threshold = (Time.now-@start_time) >= N_PLUS_ONE_TIME_THRESHOLD
end
unique_name_for(item) click to toggle source

Determine this items' “hash key”

# File lib/scout_apm/call_set.rb, line 58
def unique_name_for(item)
  item.to_s
end
update!(item = nil) click to toggle source
# File lib/scout_apm/call_set.rb, line 19
def update!(item = nil)
  if @captured # No need to do any work if we've already captured a backtrace.
    return
  end
  @call_count += 1
  @items << item
  if @grouped_items.any? # lazy grouping as normalizing items can be expensive.
    @grouped_items[unique_name_for(item)] << item
  end
end