feat(observability): more descriptive and value adding spans

This change adds more descriptive and value adding spans to
replace the generic CloudSpanner.ReadWriteTransaction.
With this change, we add new spans:
* CloudSpanner.Database.run_in_transaction
* CloudSpanner.execute_pdml
* CloudSpanner.execute_sql
* CloudSpanner.execute_update

Author: odeke-em

google/cloud/spanner_v1/_opentelemetry_tracing.py

@@ -55,15 +55,11 @@ def get_tracer(tracer_provider=None):
     return tracer_provider.get_tracer(TRACER_NAME, TRACER_VERSION)
 
 
-@contextmanager
-def trace_call(name, session=None, extra_attributes=None, observability_options=None):
-    if session:
-        session._last_use_time = datetime.now()
-
-    if not (HAS_OPENTELEMETRY_INSTALLED and name):
-        # Empty context manager. Users will have to check if the generated value is None or a span
-        yield None
-        return
+def _make_tracer_and_span_attributes(
+    session=None, extra_attributes=None, observability_options=None
+):
+    if not HAS_OPENTELEMETRY_INSTALLED:
+        return None, None
 
     tracer_provider = None
 
@@ -103,9 +99,77 @@ def trace_call(name, session=None, extra_attributes=None, observability_options=
 
     if not enable_extended_tracing:
         attributes.pop("db.statement", False)
+        attributes.pop("sql", False)
+    else:
+        # Otherwise there are places where the annotated sql was inserted
+        # directly from the arguments as "sql", and transform those into "db.statement".
+        db_statement = attributes.get("db.statement", None)
+        if not db_statement:
+            sql = attributes.get("sql", None)
+            if sql:
+                attributes = attributes.copy()
+                attributes.pop("sql", False)
+                attributes["db.statement"] = sql
+
+    return tracer, attributes
+
+
+def trace_call_end_lazily(
+    name, session=None, extra_attributes=None, observability_options=None
+):
+    """
+    trace_call_end_lazily is used in situations where you don't want a context managed
+    span in a with statement to end as soon as a block exits. This is useful for example
+    after a Database.batch or Database.snapshot but without a context manager.
+    If you need to directly invoke tracing with a context manager, please invoke
+    `trace_call` with which you can invoke
+            `with trace_call(...) as span:`
+    It is the caller's responsibility to explicitly invoke the returned ending function.
+    """
+    if not name:
+        return None
+
+    tracer, span_attributes = _make_tracer_and_span_attributes(
+        session, extra_attributes, observability_options
+    )
+    if not tracer:
+        return None
+
+    span = tracer.start_span(
+        name, kind=trace.SpanKind.CLIENT, attributes=span_attributes
+    )
+    ctx_manager = trace.use_span(span, end_on_exit=True, record_exception=True)
+    ctx_manager.__enter__()
+
+    def discard(exc_type=None, exc_value=None, exc_traceback=None):
+        if not exc_type:
+            span.set_status(Status(StatusCode.OK))
+
+        ctx_manager.__exit__(exc_type, exc_value, exc_traceback)
+
+    return discard
+
+
+@contextmanager
+def trace_call(name, session=None, extra_attributes=None, observability_options=None):
+    """
+       trace_call is used in situations where you need to end a span with a context manager
+       or after a scope is exited. If you need to keep a span alive and lazily end it, please
+       invoke `trace_call_end_lazily`.
+    """
+    if not name:
+        yield None
+        return
+
+    tracer, span_attributes = _make_tracer_and_span_attributes(
+        session, extra_attributes, observability_options
+    )
+    if not tracer:
+        yield None
+        return
 
     with tracer.start_as_current_span(
-        name, kind=trace.SpanKind.CLIENT, attributes=attributes
+        name, kind=trace.SpanKind.CLIENT, attributes=span_attributes
     ) as span:
         try:
             yield span
@@ -135,3 +199,16 @@ def get_current_span():
 def add_span_event(span, event_name, event_attributes=None):
     if span:
         span.add_event(event_name, event_attributes)
+
+
+def add_event_on_current_span(event_name, event_attributes=None, span=None):
+    if not span:
+        span = get_current_span()
+
+    add_span_event(span, event_name, event_attributes)
+
+
+def record_span_exception_and_status(span, exc):
+    if span:
+        span.set_status(Status(StatusCode.ERROR, str(exc)))
+        span.record_exception(exc)

google/cloud/spanner_v1/batch.py

@@ -26,7 +26,11 @@
     _metadata_with_prefix,
     _metadata_with_leader_aware_routing,
 )
-from google.cloud.spanner_v1._opentelemetry_tracing import trace_call
+from google.cloud.spanner_v1._opentelemetry_tracing import (
+    add_event_on_current_span,
+    trace_call,
+    trace_call_end_lazily,
+)
 from google.cloud.spanner_v1 import RequestOptions
 from google.cloud.spanner_v1._helpers import _retry
 from google.cloud.spanner_v1._helpers import _check_rst_stream_error
@@ -46,6 +50,12 @@ class _BatchBase(_SessionWrapper):
     def __init__(self, session):
         super(_BatchBase, self).__init__(session)
         self._mutations = []
+        self.__base_discard_span = trace_call_end_lazily(
+            f"CloudSpanner.{type(self).__name__}",
+            self._session,
+            None,
+            getattr(self._session._database, "observability_options", None),
+        )
 
     def _check_state(self):
         """Helper for :meth:`commit` et al.
@@ -69,6 +79,10 @@ def insert(self, table, columns, values):
         :type values: list of lists
         :param values: Values to be modified.
         """
+        add_event_on_current_span(
+            "insert mutations added",
+            dict(table=table, columns=columns),
+        )
         self._mutations.append(Mutation(insert=_make_write_pb(table, columns, values)))
         # TODO: Decide if we should add a span event per mutation:
         # https://github.com/googleapis/python-spanner/issues/1269
@@ -137,6 +151,17 @@ def delete(self, table, keyset):
         # TODO: Decide if we should add a span event per mutation:
         # https://github.com/googleapis/python-spanner/issues/1269
 
+    def _discard_on_end(self, exc_type=None, exc_val=None, exc_traceback=None):
+        if self.__base_discard_span:
+            self.__base_discard_span(exc_type, exc_val, exc_traceback)
+            self.__base_discard_span = None
+
+    def __exit__(self, exc_type=None, exc_value=None, exc_traceback=None):
+        self._discard_on_end(exc_type, exc_val, exc_traceback)
+
+    def __enter__(self):
+        return self
+
 
 class Batch(_BatchBase):
     """Accumulate mutations for transmission during :meth:`commit`."""
@@ -233,18 +258,31 @@ def commit(
             )
         self.committed = response.commit_timestamp
         self.commit_stats = response.commit_stats
+        self._discard_on_end()
         return self.committed
 
     def __enter__(self):
         """Begin ``with`` block."""
         self._check_state()
+        observability_options = getattr(
+            self._session._database, "observability_options", None
+        )
+        self.__discard_span = trace_call_end_lazily(
+            "CloudSpanner.Batch",
+            self._session,
+            observability_options=observability_options,
+        )
 
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         """End ``with`` block."""
         if exc_type is None:
             self.commit()
+        if self.__discard_span:
+            self.__discard_span(exc_type, exc_val, exc_tb)
+            self.__discard_span = None
+        self._discard_on_end()
 
 
 class MutationGroup(_BatchBase):
@@ -336,7 +374,7 @@ def batch_write(self, request_options=None, exclude_txn_from_change_streams=Fals
         )
         observability_options = getattr(database, "observability_options", None)
         with trace_call(
-            "CloudSpanner.BatchWrite",
+            "CloudSpanner.batch_write",
             self._session,
             trace_attributes,
             observability_options=observability_options,