Log a warning when an attribute is discarded due to limits

CHANGELOG.md

@@ -6,6 +6,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+- Log a warning when a `LogRecord` in `sdk/log` has dropped attributes
+  due to reaching limits
+  ([#3946](https://github.com/open-telemetry/opentelemetry-python/pull/3946))
 
 - Fix RandomIdGenerator can generate invalid Span/Trace Ids
   ([#3949](https://github.com/open-telemetry/opentelemetry-python/pull/3949))

opentelemetry-sdk/src/opentelemetry/sdk/_logs/__init__.py

@@ -15,6 +15,7 @@
 
 from opentelemetry.sdk._logs._internal import (
     LogData,
+    LogDroppedAttributesWarning,
     Logger,
     LoggerProvider,
     LoggingHandler,
@@ -31,4 +32,5 @@
     "LogLimits",
     "LogRecord",
     "LogRecordProcessor",
+    "LogDroppedAttributesWarning",
 ]

opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py

@@ -19,6 +19,7 @@
 import logging
 import threading
 import traceback
+import warnings
 from os import environ
 from time import time_ns
 from typing import Any, Callable, Optional, Tuple, Union  # noqa
@@ -57,6 +58,18 @@
 _ENV_VALUE_UNSET = ""
 
 
+class LogDroppedAttributesWarning(UserWarning):
+    """Custom warning to indicate dropped log attributes due to limits.
+
+    This class is used to filter and handle these specific warnings separately
+    from other warnings, ensuring that they are only shown once without
+    interfering with default user warnings.
+    """
+
+
+warnings.simplefilter("once", LogDroppedAttributesWarning)
+
+
 class LogLimits:
     """This class is based on a SpanLimits class in the Tracing module.
 
@@ -190,6 +203,12 @@ def __init__(
             }
         )
         self.resource = resource
+        if self.dropped_attributes > 0:
+            warnings.warn(
+                "Log record attributes were dropped due to limits",
+                LogDroppedAttributesWarning,
+                stacklevel=2,
+            )
 
     def __eq__(self, other: object) -> bool:
         if not isinstance(other, LogRecord):

opentelemetry-sdk/tests/logs/test_log_record.py

@@ -14,9 +14,14 @@
 
 import json
 import unittest
+import warnings
 
 from opentelemetry.attributes import BoundedAttributes
-from opentelemetry.sdk._logs import LogLimits, LogRecord
+from opentelemetry.sdk._logs import (
+    LogDroppedAttributesWarning,
+    LogLimits,
+    LogRecord,
+)
 
 
 class TestLogRecord(unittest.TestCase):
@@ -98,6 +103,28 @@ def test_log_record_dropped_attributes_set_limits(self):
         self.assertTrue(result.dropped_attributes == 1)
         self.assertEqual(expected, result.attributes)
 
+    def test_log_record_dropped_attributes_set_limits_warning_once(self):
+        attr = {"key1": "value1", "key2": "value2"}
+        limits = LogLimits(
+            max_attributes=1,
+            max_attribute_length=1,
+        )
+
+        with warnings.catch_warnings(record=True) as cw:
+            for _ in range(10):
+                LogRecord(
+                    timestamp=0,
+                    body="a log line",
+                    attributes=attr,
+                    limits=limits,
+                )
+        self.assertEqual(len(cw), 1)
+        self.assertIsInstance(cw[-1].message, LogDroppedAttributesWarning)
+        self.assertIn(
+            "Log record attributes were dropped due to limits",
+            str(cw[-1].message),
+        )
+
     def test_log_record_dropped_attributes_unset_limits(self):
         attr = {"key": "value", "key2": "value2"}
         limits = LogLimits()