decrement span_counter when span is compressed (#1377)

* decrement span_counter when span is compressed this ensures that compressed spans are not counted against transaction_max_spans alternative for #1376 * update changelog

Author: beniwohli

CHANGELOG.asciidoc

@@ -39,6 +39,7 @@ endif::[]
 ===== Bug fixes
 
 * Fix some context fields and metadata handling in AWS Lambda support {pull}1368[#1368]
+* Fix an issue where compressed spans would count against `transaction_max_spans` {pull}1377[#1377]
 
 [[release-notes-6.6.0]]
 ==== 6.6.0 - 2021-10-18

elasticapm/traces.py

@@ -274,7 +274,6 @@ def _begin_span(
  elif tracer.config.transaction_max_spans and self._span_counter > tracer.config.transaction_max_spans - 1:
  self.dropped_spans += 1
  span = DroppedSpan(parent_span, context=context)
- self._span_counter += 1
  else:
  span = Span(
  transaction=self,
@@ -375,7 +374,7 @@ def to_dict(self) -> dict:
  "timestamp": int(self.timestamp * 1000000), # microseconds
  "outcome": self.outcome,
  "sampled": self.is_sampled,
- "span_count": {"started": self._span_counter - self.dropped_spans, "dropped": self.dropped_spans},
+ "span_count": {"started": self._span_counter, "dropped": self.dropped_spans},
  }
  if self._dropped_span_statistics:
  result["dropped_spans_stats"] = [
@@ -639,6 +638,7 @@ def try_to_compress(self, sibling: SpanType) -> bool:
  self.composite["count"] += 1
  self.composite["sum"] += sibling.duration
  self.duration = sibling.ended_time - self.start_time
+ self.transaction._span_counter -= 1
  return True
 
  def _try_to_compress_composite(self, sibling: SpanType) -> Optional[str]:

tests/client/span_compression_tests.py

@@ -30,7 +30,7 @@
 import pytest
 
 import elasticapm
-from elasticapm.conf.constants import SPAN
+from elasticapm.conf.constants import SPAN, TRANSACTION
 
 
 @pytest.mark.parametrize(
@@ -220,3 +220,37 @@ def test_buffer_is_reported_if_next_child_ineligible(elasticapm_client):
  elasticapm_client.end_transaction("test")
  spans = elasticapm_client.events[SPAN]
  assert len(spans) == 3
+
+
+@pytest.mark.parametrize(
+ "elasticapm_client",
+ [{"span_compression_same_kind_max_duration": "5ms", "span_compression_exact_match_max_duration": "5ms"}],
+ indirect=True,
+)
+def test_compressed_spans_not_counted(elasticapm_client):
+ elasticapm_client.begin_transaction("test")
+ with elasticapm.capture_span(
+ "test1",
+ span_type="a",
+ span_subtype="b",
+ span_action="c",
+ leaf=True,
+ duration=2,
+ extra={"destination": {"service": {"resource": "x"}}},
+ ) as span1:
+ pass
+ with elasticapm.capture_span(
+ "test2",
+ span_type="a",
+ span_subtype="b",
+ span_action="c",
+ leaf=True,
+ duration=3,
+ extra={"destination": {"service": {"resource": "x"}}},
+ ) as span2:
+ pass
+ elasticapm_client.end_transaction("test")
+ transaction = elasticapm_client.events[TRANSACTION][0]
+ spans = elasticapm_client.events[SPAN]
+ assert len(spans) == transaction["span_count"]["started"] == 1
+ assert transaction["span_count"]["dropped"] == 0