sql, opt: add use_swap_mutations session variable

Release note (sql change): Add new session variable `use_swap_mutations`
which controls whether the new update swap and delete swap operators are
enabled for use by UPDATE and DELETE statements.

Author: michae2

pkg/sql/logictest/testdata/logic_test/information_schema

@@ -4289,6 +4289,7 @@ use_improved_routine_dependency_tracking                         on
 use_pre_25_2_variadic_builtins                                   off
 use_proc_txn_control_extended_protocol_fix                       on
 use_soft_limit_for_distribute_scan                               on
+use_swap_mutations                                               off
 variable_inequality_lookup_join_enabled                          on
 vector_search_beam_size                                          32
 vector_search_rerank_multiplier                                  50

pkg/sql/logictest/testdata/logic_test/pg_catalog

@@ -3243,6 +3243,7 @@ use_improved_routine_dependency_tracking                         on
 use_pre_25_2_variadic_builtins                                   off                 NULL      NULL        NULL        string
 use_proc_txn_control_extended_protocol_fix                       on                  NULL      NULL        NULL        string
 use_soft_limit_for_distribute_scan                               on                  NULL      NULL        NULL        string
+use_swap_mutations                                               off                 NULL      NULL        NULL        string
 variable_inequality_lookup_join_enabled                          on                  NULL      NULL        NULL        string
 vector_search_beam_size                                          32                  NULL      NULL        NULL        string
 vector_search_rerank_multiplier                                  50                  NULL      NULL        NULL        string
@@ -3492,6 +3493,7 @@ use_improved_routine_dependency_tracking                         on
 use_pre_25_2_variadic_builtins                                   off                 NULL  user     NULL      off                 off
 use_proc_txn_control_extended_protocol_fix                       on                  NULL  user     NULL      on                  on
 use_soft_limit_for_distribute_scan                               on                  NULL  user     NULL      on                  on
+use_swap_mutations                                               off                 NULL  user     NULL      off                 off
 variable_inequality_lookup_join_enabled                          on                  NULL  user     NULL      on                  on
 vector_search_beam_size                                          32                  NULL  user     NULL      32                  32
 vector_search_rerank_multiplier                                  50                  NULL  user     NULL      50                  50
@@ -3733,6 +3735,7 @@ use_improved_routine_dependency_tracking                         NULL    NULL
 use_pre_25_2_variadic_builtins                                   NULL    NULL     NULL     NULL        NULL
 use_proc_txn_control_extended_protocol_fix                       NULL    NULL     NULL     NULL        NULL
 use_soft_limit_for_distribute_scan                               NULL    NULL     NULL     NULL        NULL
+use_swap_mutations                                               NULL    NULL     NULL     NULL        NULL
 variable_inequality_lookup_join_enabled                          NULL    NULL     NULL     NULL        NULL
 vector_search_beam_size                                          NULL    NULL     NULL     NULL        NULL
 vector_search_rerank_multiplier                                  NULL    NULL     NULL     NULL        NULL

pkg/sql/logictest/testdata/logic_test/show_source

@@ -260,6 +260,7 @@ use_improved_routine_dependency_tracking                         on
 use_pre_25_2_variadic_builtins                                   off
 use_proc_txn_control_extended_protocol_fix                       on
 use_soft_limit_for_distribute_scan                               on
+use_swap_mutations                                               off
 variable_inequality_lookup_join_enabled                          on
 vector_search_beam_size                                          32
 vector_search_rerank_multiplier                                  50

pkg/sql/logictest/testdata/logic_test/swap_mutation

@@ -1,5 +1,8 @@
 # LogicTest: local
 
+statement ok
+SET use_swap_mutations = on
+
 # Test that unique indexes work correctly with swap mutations.
 
 statement ok
@@ -180,3 +183,6 @@ SELECT * FROM mno ORDER BY m
 ----
 3  3  3
 4  4  4
+
+statement ok
+RESET use_swap_mutations

pkg/sql/opt/exec/execbuilder/testdata/swap_mutation

@@ -1,5 +1,8 @@
 # LogicTest: local
 
+statement ok
+SET use_swap_mutations = on
+
 # Test that update swap and delete swap work correctly and use a single batch.
 
 # Test swap mutations with only primary key columns.
@@ -730,3 +733,6 @@ SELECT * FROM rstuv ORDER BY r, s
 ----
 5   6   NULL  8   NULL
 15  16  NULL  18  19
+
+statement ok
+RESET use_swap_mutations

pkg/sql/opt/memo/memo.go

@@ -216,6 +216,7 @@ type Memo struct {
 	clampInequalitySelectivity                 bool
 	useMaxFrequencySelectivity                 bool
 	usingHintInjection                         bool
+	useSwapMutations                           bool
 
 	// txnIsoLevel is the isolation level under which the plan was created. This
 	// affects the planning of some locking operations, so it must be included in
@@ -332,6 +333,7 @@ func (m *Memo) Init(ctx context.Context, evalCtx *eval.Context) {
 		clampInequalitySelectivity:                 evalCtx.SessionData().OptimizerClampInequalitySelectivity,
 		useMaxFrequencySelectivity:                 evalCtx.SessionData().OptimizerUseMaxFrequencySelectivity,
 		usingHintInjection:                         evalCtx.Planner != nil && evalCtx.Planner.UsingHintInjection(),
+		useSwapMutations:                           evalCtx.SessionData().UseSwapMutations,
 		txnIsoLevel:                                evalCtx.TxnIsoLevel,
 	}
 	m.metadata.Init()
@@ -512,6 +514,7 @@ func (m *Memo) IsStale(
 		m.clampInequalitySelectivity != evalCtx.SessionData().OptimizerClampInequalitySelectivity ||
 		m.useMaxFrequencySelectivity != evalCtx.SessionData().OptimizerUseMaxFrequencySelectivity ||
 		m.usingHintInjection != (evalCtx.Planner != nil && evalCtx.Planner.UsingHintInjection()) ||
+		m.useSwapMutations != evalCtx.SessionData().UseSwapMutations ||
 		m.txnIsoLevel != evalCtx.TxnIsoLevel {
 		return true, nil
 	}

pkg/sql/opt/norm/mutation_funcs.go

@@ -226,6 +226,10 @@ func (c *CustomFuncs) SimplifyPartialIndexProjections(
 // CanUseSwapMutation checks whether an Update or Delete can become an
 // UpdateSwap or DeleteSwap, respectively.
 func (c *CustomFuncs) CanUseSwapMutation(op opt.Operator, private *memo.MutationPrivate) bool {
+	if !c.f.evalCtx.SessionData().UseSwapMutations {
+		return false
+	}
+
 	// Checks are not currently handled by UpdateSwap or DeleteSwap.
 	if !private.CheckCols.IsEmpty() {
 		return false