Put EXPLAIN queries behind a config, defaulting to false

talisker/config.py

@@ -129,6 +129,7 @@ class Config():
         'TALISKER_NETWORKS': [],
         'TALISKER_ID_HEADER': 'X-Request-Id',
         'TALISKER_DEADLINE_HEADER': 'X-Request-Deadline',
+        'TALISKER_EXPLAIN_SQL': False,
     }
 
     Metadata = collections.namedtuple(
@@ -263,6 +264,16 @@ def slowquery_threshold(self, raw_name):
         """
         return force_int(self[raw_name])
 
+    @config_property('TALISKER_EXPLAIN_SQL')
+    def explain_sql(self, raw_name):
+        """Include EXPLAIN plans in sql sentry breadcrumbs. Defaults to false.
+
+        When enabled, this will issue extra queries to the db when generating
+        sentry reports. The EXPLAIN queries will be quick to execute, as it
+        doesn't actually run the query, but still, caution is advised.
+        """
+        return self.is_active(raw_name)
+
     @config_property('TALISKER_SOFT_REQUEST_TIMEOUT')
     def soft_request_timeout(self, raw_name):
         """Set the threshold (in ms) over which WSGI requests will report a

talisker/postgresql.py

@@ -71,6 +71,7 @@ def prettify_sql(sql):
 class TaliskerConnection(connection):
     _logger = None
     _threshold = None
+    _explain = None
     _safe_dsn = None
     _safe_dsn_format = '{user}@{host}:{port}/{dbname}'
 
@@ -99,6 +100,12 @@ def query_threshold(self):
             self._threshold = talisker.get_config().slowquery_threshold
         return self._threshold
 
+    @property
+    def explain_breadcrumbs(self):
+        if self._explain is None:
+            self._explain = talisker.get_config().explain_sql
+        return self._explain
+
     def cursor(self, *args, **kwargs):
         kwargs.setdefault('cursor_factory', TaliskerCursor)
         return super().cursor(*args, **kwargs)
@@ -129,13 +136,14 @@ def _record(self, msg, query, vars, duration, extra={}):
 
         def processor(data):
             qdata['query'] = self._format_query(query, vars)
-            try:
-                cursor = base_connection.cursor()
-                cursor.execute('EXPLAIN ' + query, vars)
-                plan = '\n'.join(l[0] for l in cursor.fetchall())
-                qdata['plan'] = plan
-            except Exception as e:
-                qdata['plan'] = 'could not explain query: ' + str(e)
+            if self.explain_breadcrumbs:
+                try:
+                    cursor = base_connection.cursor()
+                    cursor.execute('EXPLAIN ' + query, vars)
+                    plan = '\n'.join(l[0] for l in cursor.fetchall())
+                    qdata['plan'] = plan
+                except Exception as e:
+                    qdata['plan'] = 'could not explain query: ' + str(e)
 
             data['data'].update(qdata)
 

tests/test_config.py

@@ -61,6 +61,7 @@ def test_config_defaults():
         debuglog=None,
         colour=False,
         slowquery_threshold=-1,
+        explain_sql=False,
         soft_request_timeout=-1,
         request_timeout=None,
         logstatus=False,
@@ -127,6 +128,11 @@ def test_query_threshold_config():
     assert msg == "'garbage' is not a valid integer"
 
 
+def test_explain_sql_config():
+    assert_config({'TALISKER_EXPLAIN_SQL': '1'}, explain_sql=True)
+    assert_config({'TALISKER_EXPLAIN_SQL': 'garbage'}, explain_sql=False)
+
+
 def test_request_timeout_config():
     assert_config(
         {'TALISKER_SOFT_REQUEST_TIMEOUT': '3000'}, soft_request_timeout=3000)

tests/test_sentry.py

@@ -301,10 +301,11 @@ def test_sql_summary_crumb():
 
 
 @require_module('psycopg2')
-def test_sql_crumbs_functional(request, postgresql, context):
+def test_sql_crumbs_functional(request, postgresql, context, config):
     import psycopg2
     from talisker.postgresql import TaliskerConnection
 
+    config['TALISKER_EXPLAIN_SQL'] = '1'
     table = request.function.__name__
 
     with psycopg2.connect(postgresql.dsn) as ddl: