sql: add setting to enable registering latch wait contention events

This commit adds a session setting (default off) that will cause contention
events emitted by the latch table to be included in the `*_contention_events`
virtual tables. This behavior is hidden behind a setting because latch wait
events are more common than events emitted by the lock table. Tracking them
in the virtual tables could increase system load and flood the statement
insights with uninteresting events. For now, this setting does nothing, but
the following commit will use it.

Informs #103713

Release note: None

Author: DrewKimball

pkg/sql/exec_util.go

@@ -4097,6 +4097,10 @@ func (m *sessionDataMutator) SetOptimizerPlanLookupJoinsWithReverseScans(val boo
 	m.data.OptimizerPlanLookupJoinsWithReverseScans = val
 }
 
+func (m *sessionDataMutator) SetRegisterLatchWaitContentionEvents(val bool) {
+	m.data.RegisterLatchWaitContentionEvents = val
+}
+
 // Utility functions related to scrubbing sensitive information on SQL Stats.
 
 // quantizeCounts ensures that the Count field in the

pkg/sql/logictest/testdata/logic_test/information_schema

@@ -4049,6 +4049,7 @@ prefer_lookup_joins_for_fks                                off
 prepared_statements_cache_size                             0 B
 propagate_input_ordering                                   off
 recursion_depth_limit                                      1000
+register_latch_wait_contention_events                      off
 reorder_joins_limit                                        8
 require_explicit_primary_keys                              off
 results_buffer_size                                        524288

pkg/sql/logictest/testdata/logic_test/pg_catalog

@@ -3060,6 +3060,7 @@ prefer_lookup_joins_for_fks                                off                 N
 prepared_statements_cache_size                             0 B                 NULL      NULL        NULL        string
 propagate_input_ordering                                   off                 NULL      NULL        NULL        string
 recursion_depth_limit                                      1000                NULL      NULL        NULL        string
+register_latch_wait_contention_events                      off                 NULL      NULL        NULL        string
 reorder_joins_limit                                        8                   NULL      NULL        NULL        string
 require_explicit_primary_keys                              off                 NULL      NULL        NULL        string
 results_buffer_size                                        524288              NULL      NULL        NULL        string
@@ -3270,6 +3271,7 @@ prefer_lookup_joins_for_fks                                off                 N
 prepared_statements_cache_size                             0 B                 NULL  user     NULL      0 B                 0 B
 propagate_input_ordering                                   off                 NULL  user     NULL      off                 off
 recursion_depth_limit                                      1000                NULL  user     NULL      1000                1000
+register_latch_wait_contention_events                      off                 NULL  user     NULL      off                 off
 reorder_joins_limit                                        8                   NULL  user     NULL      8                   8
 require_explicit_primary_keys                              off                 NULL  user     NULL      off                 off
 results_buffer_size                                        524288              NULL  user     NULL      524288              524288
@@ -3479,6 +3481,7 @@ prefer_lookup_joins_for_fks                                NULL    NULL     NULL
 prepared_statements_cache_size                             NULL    NULL     NULL     NULL        NULL
 propagate_input_ordering                                   NULL    NULL     NULL     NULL        NULL
 recursion_depth_limit                                      NULL    NULL     NULL     NULL        NULL
+register_latch_wait_contention_events                      NULL    NULL     NULL     NULL        NULL
 reorder_joins_limit                                        NULL    NULL     NULL     NULL        NULL
 require_explicit_primary_keys                              NULL    NULL     NULL     NULL        NULL
 results_buffer_size                                        NULL    NULL     NULL     NULL        NULL

pkg/sql/logictest/testdata/logic_test/show_source

@@ -176,6 +176,7 @@ prefer_lookup_joins_for_fks                                off
 prepared_statements_cache_size                             0 B
 propagate_input_ordering                                   off
 recursion_depth_limit                                      1000
+register_latch_wait_contention_events                      off
 reorder_joins_limit                                        8
 require_explicit_primary_keys                              off
 results_buffer_size                                        524288

pkg/sql/sessiondatapb/local_only_session_data.proto

@@ -617,6 +617,11 @@ message LocalOnlySessionData {
   // that use reverse scans to get results in reverse index order on each
   // lookup.
   bool optimizer_plan_lookup_joins_with_reverse_scans = 158;
+  // RegisterLatchWaitContentionEvents, when true, causes latch wait contention
+  // events to be registered with the *.contention_events virtual tables. It
+  // defaults to false in order to avoid registering a large number of
+  // uninformative latch wait events.
+  bool register_latch_wait_contention_events = 159;
 
   ///////////////////////////////////////////////////////////////////////////
   // WARNING: consider whether a session parameter you're adding needs to  //

pkg/sql/vars.go

@@ -3840,6 +3840,23 @@ var varGen = map[string]sessionVar{
 		},
 		GlobalDefault: globalTrue,
 	},
+
+	// CockroachDB extension.
+	`register_latch_wait_contention_events`: {
+		GetStringVal: makePostgresBoolGetStringValFn(`register_latch_wait_contention_events`),
+		Set: func(_ context.Context, m sessionDataMutator, s string) error {
+			b, err := paramparse.ParseBoolVar("register_latch_wait_contention_events", s)
+			if err != nil {
+				return err
+			}
+			m.SetRegisterLatchWaitContentionEvents(b)
+			return nil
+		},
+		Get: func(evalCtx *extendedEvalContext, _ *kv.Txn) (string, error) {
+			return formatBoolAsPostgresSetting(evalCtx.SessionData().RegisterLatchWaitContentionEvents), nil
+		},
+		GlobalDefault: globalFalse,
+	},
 }
 
 func ReplicationModeFromString(s string) (sessiondatapb.ReplicationMode, error) {