Class: ScoutApm::TrackedRequest

Inherits:
Object
  • Object
show all
Defined in:
lib/scout_apm/tracked_request.rb

Constant Summary collapse

REQUEST_TYPES =

When we see these layers, it means a real request is going through the system. We toggle a flag to turn on some slightly more expensive instrumentation (backtrace collection and the like) that would be too expensive in situations where the framework is constantly churning. We see that on Sidekiq.

["Controller", "Job"]
BACKTRACE_BLACKLIST =
["Controller", "Job"]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(agent_context, store) ⇒ TrackedRequest

Returns a new instance of TrackedRequest.



55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
# File 'lib/scout_apm/tracked_request.rb', line 55

def initialize(agent_context, store)
  @agent_context = agent_context
  @store = store #this is passed in so we can use a real store (normal operation) or fake store (instant mode only)
  @layers = []
  @call_set = Hash.new { |h, k| h[k] = CallSet.new }
  @annotations = {}
  @ignoring_children = 0
  @context = Context.new(agent_context)
  @root_layer = nil
  @error = false
  @stopping = false
  @instant_key = nil
  @mem_start = mem_usage
  @recorder = agent_context.recorder
  @real_request = false
  @transaction_id = ScoutApm::Utils::TransactionId.new.to_s
  ignore_request! if @recorder.nil?
end

Instance Attribute Details

#annotationsObject (readonly)

As we go through a request, instrumentation can mark more general data into the Request Known Keys:

:uri - the full URI requested by the user
:queue_latency - how long a background Job spent in the queue before starting processing


23
24
25
# File 'lib/scout_apm/tracked_request.rb', line 23

def annotations
  @annotations
end

#call_countsObject

This maintains a lookup hash of Layer names and call counts. It’s used to trigger fetching a backtrace on n+1 calls. Note that layer names might not be Strings - can alse be Utils::ActiveRecordMetricName. Also, this would fail for layers with same names across multiple types.



32
33
34
# File 'lib/scout_apm/tracked_request.rb', line 32

def call_counts
  @call_counts
end

#contextObject (readonly)

Context is application defined extra information. (ie, which user, what is their email/ip, what plan are they on, what locale are they using, etc) See documentation for examples on how to set this from a before_filter



13
14
15
# File 'lib/scout_apm/tracked_request.rb', line 13

def context
  @context
end

#headersObject (readonly)

Headers as recorded by rails Can be nil if we never reach a Rails Controller



27
28
29
# File 'lib/scout_apm/tracked_request.rb', line 27

def headers
  @headers
end

#instant_keyObject

if there’s an instant_key, pass the transaction trace on for immediate reporting (in addition to the usual background aggregation) this is set in the controller instumentation (ActionControllerRails3Rails4 according)



36
37
38
# File 'lib/scout_apm/tracked_request.rb', line 36

def instant_key
  @instant_key
end

#name_overrideObject

If specified, an override for the name of the request. If unspecified, the name is determined from the name of the Controller or Job layer.



43
44
45
# File 'lib/scout_apm/tracked_request.rb', line 43

def name_override
  @name_override
end

#recorderObject (readonly)

An object that responds to ‘record!(TrackedRequest)` to store this tracked request



39
40
41
# File 'lib/scout_apm/tracked_request.rb', line 39

def recorder
  @recorder
end

#root_layerObject (readonly)

The first layer registered with this request. All other layers will be children of this layer.



17
18
19
# File 'lib/scout_apm/tracked_request.rb', line 17

def root_layer
  @root_layer
end

#transaction_idObject (readonly)

A unique, but otherwise meaningless String to identify this request. UUID



46
47
48
# File 'lib/scout_apm/tracked_request.rb', line 46

def transaction_id
  @transaction_id
end

Instance Method Details

#acknowledge_children!Object



411
412
413
414
415
# File 'lib/scout_apm/tracked_request.rb', line 411

def acknowledge_children!
  if @ignoring_children > 0
    @ignoring_children -= 1
  end
end

#annotate_request(hsh) ⇒ Object

As we learn things about this request, we can add data here. For instance, when we know where Rails routed this request to, we can store that scope info. Or as soon as we know which URI it was directed at, we can store that.

This data is internal to ScoutApm, to add custom information, use the Context api.



233
234
235
# File 'lib/scout_apm/tracked_request.rb', line 233

def annotate_request(hsh)
  @annotations.merge!(hsh)
end

#backtrace_thresholdObject

Grab backtraces more aggressively when running in dev trace mode



178
179
180
# File 'lib/scout_apm/tracked_request.rb', line 178

def backtrace_threshold
  @agent_context.dev_trace_enabled? ? 0.05 : 0.5 # the minimum threshold in seconds to record the backtrace for a metric.
end

#capture_backtrace?(layer) ⇒ Boolean

Returns:

  • (Boolean)


150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
# File 'lib/scout_apm/tracked_request.rb', line 150

def capture_backtrace?(layer)
  return if ignoring_request?

  # Never capture backtraces for this kind of layer. The backtrace will
  # always be 100% framework code.
  return false if BACKTRACE_BLACKLIST.include?(layer.type)

  # Only capture backtraces if we're in a real "request". Otherwise we
  # can spend lot of time capturing backtraces from the internals of
  # Sidekiq, only to throw them away immediately.
  return false unless real_request?

  # Capture any individually slow layer.
  return true if layer.total_exclusive_time > backtrace_threshold

  # Capture any layer that we've seen many times. Captures n+1 problems
  return true if @call_set[layer.name].capture_backtrace?

  # Don't capture otherwise
  false
end

#capture_mem_delta!Object



188
189
190
# File 'lib/scout_apm/tracked_request.rb', line 188

def capture_mem_delta!
  @mem_delta = mem_usage - @mem_start
end

#current_layerObject

Grab the currently running layer. Useful for adding additional data as we learn it. This is useful in ActiveRecord instruments, where we start the instrumentation early, and gradually learn more about the request that actually happened as we go (for instance, the # of records found, or the actual SQL generated).

Returns nil in the case there is no current layer. That would be normal for a completed TrackedRequest



145
146
147
# File 'lib/scout_apm/tracked_request.rb', line 145

def current_layer
  @layers.last
end

#ensure_background_workerObject

Ensure the background worker thread is up & running - a fallback if other detection doesn’t achieve this at boot.



349
350
351
352
353
354
# File 'lib/scout_apm/tracked_request.rb', line 349

def ensure_background_worker
  agent = ScoutApm::Agent.instance
  agent.start
rescue => e
  true
end

#error!Object

This request had an exception. Mark it down as an error



238
239
240
# File 'lib/scout_apm/tracked_request.rb', line 238

def error!
  @error = true
end

#error?Boolean

Returns:

  • (Boolean)


242
243
244
# File 'lib/scout_apm/tracked_request.rb', line 242

def error?
  @error
end

#finalized?Boolean

Are we finished with this request? We’re done if we have no layers left after popping one off

Returns:

  • (Boolean)


198
199
200
# File 'lib/scout_apm/tracked_request.rb', line 198

def finalized?
  @layers.none?
end

#ignore_children!Object

Enable this when you would otherwise double track something interesting. This came up when we implemented InfluxDB instrumentation, which is more specific, and useful than the fact that InfluxDB happens to use Net::HTTP internally

When enabled, new layers won’t be added to the current Request, and calls to stop_layer will be ignored.

Do not forget to turn if off when leaving a layer, it is the instrumentation’s task to do that.

When you use this in code, be sure to use it in this order:

start_layer ignore_children

-> call

acknowledge_children stop_layer

If you don’t call it in this order, it’s possible to get out of sync, and have an ignored start and an actually-executed stop, causing layers to get out of sync



407
408
409
# File 'lib/scout_apm/tracked_request.rb', line 407

def ignore_children!
  @ignoring_children += 1
end

#ignore_request!Object

At any point in the request, calling code or instrumentation can call ‘ignore_request!` to immediately stop recording any information about new layers, and delete any existing layer info. This class will still exist, and respond to methods as normal, but `record!` won’t be called, and no data will be recorded.

We still need to keep track of the current layer depth (via “reported”, and ready to be recreated for the next request.



435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
# File 'lib/scout_apm/tracked_request.rb', line 435

def ignore_request!
  return if @ignoring_request

  # Set instance variable
  @ignoring_request = true

  # Store data we'll need
  @ignoring_depth = @layers.length

  # Clear data
  @layers = []
  @root_layer = nil
  @call_set = nil
  @annotations = {}
  @instant_key = nil
end

#ignoring_children?Boolean

Returns:

  • (Boolean)


417
418
419
# File 'lib/scout_apm/tracked_request.rb', line 417

def ignoring_children?
  @ignoring_children > 0
end

#ignoring_recorded?Boolean

Returns:

  • (Boolean)


464
465
466
# File 'lib/scout_apm/tracked_request.rb', line 464

def ignoring_recorded?
  @ignoring_depth <= 0
end

#ignoring_request?Boolean

Returns:

  • (Boolean)


452
453
454
# File 'lib/scout_apm/tracked_request.rb', line 452

def ignoring_request?
  @ignoring_request
end

#ignoring_start_layerObject



456
457
458
# File 'lib/scout_apm/tracked_request.rb', line 456

def ignoring_start_layer
  @ignoring_depth += 1
end

#ignoring_stop_layerObject



460
461
462
# File 'lib/scout_apm/tracked_request.rb', line 460

def ignoring_stop_layer
  @ignoring_depth -= 1
end

#instant?Boolean

Returns:

  • (Boolean)


250
251
252
253
254
# File 'lib/scout_apm/tracked_request.rb', line 250

def instant?
  return false if ignoring_request?

  instant_key
end

#job?Boolean

This request is a job transaction iff it has a ‘Job’ layer Use this only during recording

Returns:

  • (Boolean)


332
333
334
# File 'lib/scout_apm/tracked_request.rb', line 332

def job?
  layer_finder.job != nil
end

#layer_finderObject



343
344
345
# File 'lib/scout_apm/tracked_request.rb', line 343

def layer_finder
  @layer_finder ||= LayerConverters::FindLayerByType.new(self)
end

#loggerObject



468
469
470
# File 'lib/scout_apm/tracked_request.rb', line 468

def logger
  @agent_context.logger
end

#mem_usageObject

This may be in bytes or KB based on the OSX. We store this as-is here and only do conversion to MB in Layer Converters. XXX: Move this to environment?



184
185
186
# File 'lib/scout_apm/tracked_request.rb', line 184

def mem_usage
  ScoutApm::Instruments::Process::ProcessMemory.new(@agent_context).rss
end

#prepare_to_dump!Object

Actually go fetch & make-real any lazily created data. Clean up any cleverness in objects. Makes this object ready to be Marshal Dumped (or otherwise serialized)



479
480
481
482
483
484
# File 'lib/scout_apm/tracked_request.rb', line 479

def prepare_to_dump!
  @call_set = nil
  @store = nil
  @recorder = nil
  @agent_context = nil
end

#real_request!Object



128
129
130
# File 'lib/scout_apm/tracked_request.rb', line 128

def real_request!
  @real_request = true
end

#real_request?Boolean

Have we seen a “controller” or “job” layer so far?

Returns:

  • (Boolean)


133
134
135
# File 'lib/scout_apm/tracked_request.rb', line 133

def real_request?
  @real_request
end

#record!Object

Convert this request to the appropriate structure, then report it into the peristent Store object



266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
# File 'lib/scout_apm/tracked_request.rb', line 266

def record!
  recorded!

  return if ignoring_request?

  # If we didn't have store, but we're trying to record anyway, go
  # figure that out. (this happens in Remote Agent scenarios)
  restore_from_dump! if @agent_context.nil?

  # Bail out early if the user asked us to ignore this uri
  return if @agent_context.ignored_uris.ignore?(annotations[:uri])

  apply_name_override

  @agent_context.transaction_time_consumed.add(unique_name, root_layer.total_call_time)

  context.add(:transaction_id => transaction_id)

  # Make a constant, then call converters.dup.each so it isn't inline?
  converters = {
    :histograms => LayerConverters::Histograms,
    :metrics => LayerConverters::MetricConverter,
    :errors => LayerConverters::ErrorConverter,
    :allocation_metrics => LayerConverters::AllocationMetricConverter,
    :queue_time => LayerConverters::RequestQueueTimeConverter,
    :job => LayerConverters::JobConverter,
    :db => LayerConverters::DatabaseConverter,

    :slow_job => LayerConverters::SlowJobConverter,
    :slow_req => LayerConverters::SlowRequestConverter,

    # This is now integrated into the slow_job and slow_req converters, so that
    # we get the exact same set of traces either way. We can call it
    # directly when we move away from the legacy trace styles.
    # :traces => LayerConverters::TraceConverter,
  }

  walker = LayerConverters::DepthFirstWalker.new(self.root_layer)
  converter_instances = converters.inject({}) do |memo, (slug, klass)|
    instance = klass.new(@agent_context, self, layer_finder, @store)
    instance.register_hooks(walker)
    memo[slug] = instance
    memo
  end
  walker.walk
  converter_results = converter_instances.inject({}) do |memo, (slug,i)| 
    memo[slug] = i.record!
    memo
  end

  @agent_context.extensions.run_transaction_callbacks(converter_results,context,layer_finder.scope)

  # If there's an instant_key, it means we need to report this right away
  if web? && instant?
    converter = converters.find{|c| c.class == LayerConverters::SlowRequestConverter}
    trace = converter.call
    ScoutApm::InstantReporting.new(trace, instant_key).call
  end

  if web? || job?
    ensure_background_worker
  end
end

#recorded!Object

Persist the Request



260
261
262
# File 'lib/scout_apm/tracked_request.rb', line 260

def recorded!
  @recorded = true
end

#recorded?Boolean

Have we already persisted this request? Used to know when we should just create a new one (don’t attempt to add data to an already-recorded request). See RequestManager

Returns:

  • (Boolean)


374
375
376
377
378
# File 'lib/scout_apm/tracked_request.rb', line 374

def recorded?
  return ignoring_recorded? if ignoring_request?

  @recorded
end

#restore_from_dump!Object

Go re-fetch the store based on what the Agent’s official one is. Used after hydrating a dumped TrackedRequest



488
489
490
491
492
# File 'lib/scout_apm/tracked_request.rb', line 488

def restore_from_dump!
  @agent_context = ScoutApm::Agent.instance.context
  @recorder = @agent_context.recorder
  @store = @agent_context.store
end

#set_headers(headers) ⇒ Object



246
247
248
# File 'lib/scout_apm/tracked_request.rb', line 246

def set_headers(headers)
  @headers = headers
end

#start_layer(layer) ⇒ Object



74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
# File 'lib/scout_apm/tracked_request.rb', line 74

def start_layer(layer)
  # If we're already stopping, don't do additional layers
  return if stopping?

  return if ignoring_children?

  return ignoring_start_layer if ignoring_request?

  start_request(layer) unless @root_layer

  if REQUEST_TYPES.include?(layer.type)
    real_request!
  end
  @layers.push(layer)
end

#start_request(layer) ⇒ Object

Run at the beginning of the whole request

  • Capture the first layer as the root_layer



205
206
207
# File 'lib/scout_apm/tracked_request.rb', line 205

def start_request(layer)
  @root_layer = layer unless @root_layer # capture root layer
end

#stop_layerObject



90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
# File 'lib/scout_apm/tracked_request.rb', line 90

def stop_layer
  # If we're already stopping, don't do additional layers
  return if stopping?

  return if ignoring_children?

  return ignoring_stop_layer if ignoring_request?

  layer = @layers.pop

  # Safeguard against a mismatch in the layer tracking in an instrument.
  # This class works under the assumption that start & stop layers are
  # lined up correctly. If stop_layer gets called twice, when it should
  # only have been called once you'll end up with this error.
  if layer.nil?
    logger.warn("Error stopping layer, was nil. Root Layer: #{@root_layer.inspect}")
    stop_request
    return
  end

  layer.record_stop_time!
  layer.record_allocations!

  @layers[-1].add_child(layer) if @layers.any?

  # This must be called before checking if a backtrace should be collected as the call count influences our capture logic.
  # We call `#update_call_counts in stop layer to ensure the layer has a final desc. Layer#desc is updated during the AR instrumentation flow.
  update_call_counts!(layer)
  if capture_backtrace?(layer)
    layer.capture_backtrace!
  end


  if finalized?
    stop_request
  end
end

#stop_requestObject

Run at the end of the whole request

  • Send the request off to be stored



212
213
214
215
216
217
218
# File 'lib/scout_apm/tracked_request.rb', line 212

def stop_request
  @stopping = true

  if @recorder
    @recorder.record!(self)
  end
end

#stopping?Boolean

Returns:

  • (Boolean)


220
221
222
# File 'lib/scout_apm/tracked_request.rb', line 220

def stopping?
  @stopping
end

#unique_nameObject

Only call this after the request is complete



358
359
360
361
362
363
364
365
366
367
368
369
# File 'lib/scout_apm/tracked_request.rb', line 358

def unique_name
  return nil if ignoring_request?

  @unique_name ||= begin
                     scope_layer = LayerConverters::FindLayerByType.new(self).scope
                     if scope_layer
                       scope_layer.legacy_metric_name
                     else
                       :unknown
                     end
                   end
end

#update_call_counts!(layer) ⇒ Object

Maintains a lookup Hash of call counts by layer name. Used to determine if we should capture a backtrace.



173
174
175
# File 'lib/scout_apm/tracked_request.rb', line 173

def update_call_counts!(layer)
  @call_set[layer.name].update!(layer.desc)
end

#web?Boolean

This request is a web transaction iff it has a ‘Controller’ layer Use this only during recording

Returns:

  • (Boolean)


338
339
340
# File 'lib/scout_apm/tracked_request.rb', line 338

def web?
  layer_finder.controller != nil
end