Class: NewRelic::Agent::TransactionSampler

Inherits:
Object
  • Object
show all
Defined in:
lib/new_relic/agent/transaction_sampler.rb

Overview

This class contains the logic of sampling a transaction - creation and modification of transaction samples

Defined Under Namespace

Modules: Shim

Constant Summary collapse

BUILDER_KEY = 
:transaction_sample_builder
MAX_DATA_LENGTH = 
16384

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ TransactionSampler

Returns a new instance of TransactionSampler.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 27

def initialize
  # @samples is an array of recent samples up to @max_samples in
  # size - it's only used by developer mode
  @samples = []
  @force_persist = []
  @max_samples = 100

  # @harvest_count is a count of harvests used for random
  # sampling - we pull 1 @random_sample in every @sampling_rate harvests
  @harvest_count = 0
  @random_sample = nil
  @sampling_rate = 10
  @slow_capture_threshold = 2.0
  configure!

  # This lock is used to synchronize access to the @last_sample
  # and related variables. It can become necessary on JRuby or
  # any 'honest-to-god'-multithreaded system
  @samples_lock = Mutex.new
end

Instance Attribute Details

#disabled ⇒ Object (readonly)

Returns the value of attribute disabled.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 25

def disabled
  @disabled
end

#explain_enabled ⇒ Object

Returns the value of attribute explain_enabled.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 23

def explain_enabled
  @explain_enabled
end

#explain_threshold ⇒ Object

Returns the value of attribute explain_threshold.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 23

def explain_threshold
  @explain_threshold
end

#last_sample ⇒ Object (readonly)

Returns the value of attribute last_sample.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 25

def last_sample
  @last_sample
end

#random_sampling ⇒ Object

Returns the value of attribute random_sampling.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 22

def random_sampling
  @random_sampling
end

#samples ⇒ Object (readonly)

Returns the value of attribute samples.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 25

def samples
  @samples
end

#sampling_rate ⇒ Object

Returns the value of attribute sampling_rate.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 22

def sampling_rate
  @sampling_rate
end

#slow_capture_threshold ⇒ Object

Returns the value of attribute slow_capture_threshold.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 24

def slow_capture_threshold
  @slow_capture_threshold
end

#stack_trace_threshold ⇒ Object

Returns the value of attribute stack_trace_threshold.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 22

def stack_trace_threshold
  @stack_trace_threshold
end

#transaction_threshold ⇒ Object

Returns the value of attribute transaction_threshold.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 23

def transaction_threshold
  @transaction_threshold
end

Instance Method Details

#add_force_persist_to(result) ⇒ Object 



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 351

def add_force_persist_to(result)
  result.concat(@force_persist)
  @force_persist = []
end

#add_random_sample_to(result) ⇒ Object

Every 1/n harvests, adds the most recent sample to the harvest array if it exists. Makes sure that the random sample is not also the slowest sample for this harvest by ‘uniq!`ing the result array

random sampling is very, very seldom used



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 341

def add_random_sample_to(result)
  return unless @random_sampling && @sampling_rate && @sampling_rate.to_i > 0
  @harvest_count += 1
  if (@harvest_count.to_i % @sampling_rate.to_i) == 0
    result << @random_sample if @random_sample
    @harvest_count = 0
  end
  nil # don't assume this method returns anything
end

#add_samples_to(result, slow_threshold) ⇒ Object

Returns an array of slow samples, with either one or two elements - one element unless random sampling is enabled. The sample returned will be the slowest sample among those available during this harvest



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 360

def add_samples_to(result, slow_threshold)
  
  # pull out force persist
  force_persist = result.select {|sample| sample.force_persist} || []
  result.reject! {|sample| sample.force_persist}
  
  force_persist.each {|sample| store_force_persist(sample)}
  
  
  # Now get the slowest sample
  if @slowest_sample && @slowest_sample.duration >= slow_threshold
    result << @slowest_sample
  end

  result.compact!
  result = result.sort_by { |x| x.duration }
  result = result[-1..-1] || []               # take the slowest sample
  
  add_random_sample_to(result)
  add_force_persist_to(result)
  
  result.uniq
end

#append_backtrace(segment, duration) ⇒ Object

Appends a backtrace to a segment if that segment took longer than the specified duration



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 313

def append_backtrace(segment, duration)
  segment[:backtrace] = caller.join("\n") if (duration >= @stack_trace_threshold || Thread.current[:capture_deep_tt])
end

#append_new_message(old_message, message) ⇒ Object

Allows the addition of multiple pieces of metadata to one segment - i.e. traced method calls multiple sql queries



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 303

def append_new_message(old_message, message)
  if old_message
    old_message + ";\n" + message
  else
    message
  end
end

#builder ⇒ Object

The current thread-local transaction sample builder



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 451

def builder
  Thread::current[BUILDER_KEY]
end

#capture_segment_trace ⇒ Object

in developer mode, capture the stack trace with the segment. this is cpu and memory expensive and therefore should not be turned on in production mode



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 123

def capture_segment_trace
  return unless NewRelic::Control.instance.developer_mode?
  segment = builder.current_segment
  if segment
    # Strip stack frames off the top that match /new_relic/agent/
    trace = caller
    while trace.first =~/\/lib\/new_relic\/agent\//
      trace.shift
    end

    trace = trace[0..39] if trace.length > 40
    segment[:backtrace] = trace
  end
end

#clamp_number_tts(tts, limit) ⇒ Object

JON - THIS CODE NEEDS A UNIT TEST



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 412

def clamp_number_tts(tts, limit)
  tts.sort! do |a,b|
    if a.force_persist && b.force_persist
      b.duration <=> a.duration
    elsif a.force_persist
      -1
    elsif b.force_persist
      1
    else
      b.duration <=> a.duration
    end
  end        
  
  tts[0..(limit-1)]  
end

#clear_builder ⇒ Object

Sets the thread local variable storing the transaction sample builder to nil to clear it



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 457

def clear_builder
  Thread::current[BUILDER_KEY] = nil
end

#config ⇒ Object 



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 62

def config
  NewRelic::Control.instance.fetch('transaction_tracer', {})
end

#configure! ⇒ Object 



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 48

def configure!
  # @segment_limit and @stack_trace_threshold come from the
  # configuration file, with built-in defaults that should
  # suffice for most customers
  
  # enable if config.fetch('enabled', true)
  
  @segment_limit = config.fetch('limit_segments', 4000)
  @stack_trace_threshold = config.fetch('stack_trace_threshold', 0.500).to_f
  @explain_threshold = config.fetch('explain_threshold', 0.5).to_f
  @explain_enabled = config.fetch('explain_enabled', true)
  @transaction_threshold = config.fetch('transation_threshold', 2.0)
end

#current_sample_id ⇒ Object

Returns the current sample id, delegated from ‘builder`



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 67

def current_sample_id
  b=builder
  b and b.sample_id
end

#disable ⇒ Object

Disable the transaction sampler - this also deregisters it with the statistics engine.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 81

def disable
  @disabled = true
  NewRelic::Agent.instance.stats_engine.remove_transaction_sampler(self)
end

#enable ⇒ Object

Enable the transaction sampler - this also registers it with the statistics engine.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 74

def enable
  @disabled = false
  NewRelic::Agent.instance.stats_engine.transaction_sampler = self
end

#enabled? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/new_relic/agent/transaction_sampler.rb', line 86

def enabled?
  !@disabled
end

#harvest(previous = [], slow_threshold = 2.0) ⇒ Object

get the set of collected samples, merging into previous samples, and clear the collected sample list. Truncates samples to a specified @segment_limit to save memory and bandwith transmitting samples to the server.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 388

def harvest(previous = [], slow_threshold = 2.0)
  return [] if disabled
  result = Array(previous)
  
  @samples_lock.synchronize do
    result = add_samples_to(result, slow_threshold)
              
    # clear previous transaction samples
    @slowest_sample = nil
    @random_sample = nil
    @last_sample = nil
  end
  
  # Clamp the number of TTs we'll keep in memory and send
  #
  result = clamp_number_tts(result, 20) if result.length > 20
  
  # Truncate the samples at 2100 segments. The UI will clamp them at 2000 segments anyway.
  # This will save us memory and bandwidth.
  result.each { |sample| sample.truncate(@segment_limit) }
  result
end

#ignore_transaction ⇒ Object

Tells the builder to ignore a transaction, if we are currently creating one. Only causes the sample to be ignored upon end of the transaction, and does not change the metrics gathered outside of the sampler



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 252

def ignore_transaction
  builder.ignore_transaction if builder
end

#notice_first_scope_push(time) ⇒ Object

Creates a new transaction sample builder, unless the transaction sampler is disabled. Takes a time parameter for the start of the transaction sample



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 102

def notice_first_scope_push(time)
  start_builder(time.to_f) unless disabled
end

#notice_nosql(key, duration) ⇒ Object

Adds non-sql metadata to a segment - generally the memcached key

duration is seconds, float value.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 331

def notice_nosql(key, duration)
  notice_extra_data(key, duration, :key)
end

#notice_pop_scope(scope, time = Time.now) ⇒ Object

Informs the transaction sample builder about the end of a traced scope



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 148

def notice_pop_scope(scope, time = Time.now)
  return unless builder
  raise "frozen already???" if builder.sample.frozen?
  builder.trace_exit(scope, time.to_f)
end

#notice_profile(profile) ⇒ Object

For developer mode profiling support - delegates to the builder



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 257

def notice_profile(profile)
  builder.set_profile(profile) if builder
end

#notice_push_scope(scope, time = Time.now) ⇒ Object

This delegates to the builder to create a new open transaction segment for the specified scope, beginning at the optionally specified time.

Note that in developer mode, this captures a stacktrace for the beginning of each segment, which can be fairly slow



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 112

def notice_push_scope(scope, time=Time.now)
  return unless builder

  builder.trace_entry(scope, time.to_f)

  capture_segment_trace if NewRelic::Control.instance.developer_mode?
end

#notice_scope_empty(time = Time.now) ⇒ Object

This is called when we are done with the transaction. We’ve unwound the stack to the top level. It also clears the transaction sample builder so that it won’t continue to have scopes appended to it.

It sets various instance variables to the finished sample, depending on which settings are active. See ‘store_sample`



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 161

def notice_scope_empty(time=Time.now)

  last_builder = builder
  return unless last_builder

  last_builder.finish_trace(time.to_f)
  clear_builder
  return if last_builder.ignored?

  @samples_lock.synchronize do
    # NB this instance variable may be used elsewhere, it's not
    # just a side effect
    @last_sample = last_builder.sample
    store_sample(@last_sample)
  end
end

#notice_sql(sql, config, duration) ⇒ Object

some statements (particularly INSERTS with large BLOBS may be very large; we should trim them to a maximum usable length config is the driver configuration for the connection duration is seconds, float value.



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 321

def notice_sql(sql, config, duration)
  if NewRelic::Agent.is_sql_recorded?
    notice_extra_data(sql, duration, :sql, config, :connection_config)
  end
end

#notice_transaction(path, uri = nil, params = {}) ⇒ Object

Delegates to the builder to store the path, uri, and parameters if the sampler is active



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 244

def notice_transaction(path, uri=nil, params={})
  builder.set_transaction_info(path, uri, params) if !disabled && builder
end

#notice_transaction_cpu_time(cpu_time) ⇒ Object

Sets the CPU time used by a transaction, delegates to the builder



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 262

def notice_transaction_cpu_time(cpu_time)
  builder.set_transaction_cpu_time(cpu_time) if builder
end

#reset! ⇒ Object

reset samples without rebooting the web server



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 429

def reset!
  @samples = []
  @last_sample = nil
  @random_sample = nil
  @slowest_sample = nil
end

#scope_depth ⇒ Object

Defaults to zero, otherwise delegated to the transaction sample builder



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 140

def scope_depth
  return 0 unless builder

  builder.scope_depth
end

#slowest_sample?(old_sample, new_sample) ⇒ Boolean

Checks to see if the old sample exists, or if it’s duration is less than the new sample

Returns:

  • (Boolean) 


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# File 'lib/new_relic/agent/transaction_sampler.rb', line 230

def slowest_sample?(old_sample, new_sample)
  old_sample.nil? || (new_sample.duration > old_sample.duration)
end

#start_builder(time = nil) ⇒ Object

Checks to see if the transaction sampler is disabled, if transaction trace recording is disabled by a thread local, or if execution is untraced - if so it clears the transaction sample builder from the thread local, otherwise it generates a new transaction sample builder with the stated time as a starting point and saves it in the thread local variable



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 442

def start_builder(time=nil)
  if disabled || !NewRelic::Agent.is_transaction_traced? || !NewRelic::Agent.is_execution_traced?
    clear_builder
  else
    Thread::current[BUILDER_KEY] ||= TransactionSampleBuilder.new(time)
  end
end

#store_force_persist(sample) ⇒ Object 



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 201

def store_force_persist(sample)
  @force_persist << sample

  # WARNING - this clamp should be configurable
  if @force_persist.length > 15
    @force_persist.sort! {|a,b| b.duration <=> a.duration}
    @force_persist = @force_persist[0..14]
  end
end

#store_random_sample(sample) ⇒ Object

Only active when random sampling is true - this is very rarely used. Always store the most recent sample so that random sampling can pick a few of the samples to store, upon harvest



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 195

def store_random_sample(sample)
  if @random_sampling
    @random_sample = sample
  end
end

#store_sample(sample) ⇒ Object

Samples can be stored in three places: the random sample variable, when random sampling is active, the developer mode slower than the current occupant of that slot



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 182

def store_sample(sample)
  store_random_sample(sample)
  store_sample_for_developer_mode(sample)
  store_slowest_sample(sample)
  
  if NewRelic::Agent::TransactionInfo.get.force_persist_sample?(sample)
    store_force_persist(sample)
  end
end

#store_sample_for_developer_mode(sample) ⇒ Object

Samples take up a ton of memory, so we only store a lot of them in developer mode - we truncate to @max_samples



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 213

def store_sample_for_developer_mode(sample)
  return unless NewRelic::Control.instance.developer_mode?
  @samples = [] unless @samples
  @samples << sample
  truncate_samples
end

#store_slowest_sample(sample) ⇒ Object

Sets @slowest_sample to the passed in sample if it is slower than the current sample in @slowest_sample



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 222

def store_slowest_sample(sample)
  if slowest_sample?(@slowest_sample, sample)
    @slowest_sample = sample
  end
end

#truncate_message(message) ⇒ Object

Truncates the message to ‘MAX_DATA_LENGTH` if needed, and appends an ellipsis because it makes the trucation clearer in the UI



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 293

def truncate_message(message)
  if message.length > (MAX_DATA_LENGTH - 4)
    message[0..MAX_DATA_LENGTH - 4] + '...'
  else
    message
  end
end

#truncate_samples ⇒ Object

Smashes the @samples array down to the length of @max_samples by taking the last @max_samples elements of the array



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# File 'lib/new_relic/agent/transaction_sampler.rb', line 236

def truncate_samples
  if @samples.length > @max_samples
    @samples = @samples[-@max_samples..-1]
  end
end