sql: use soft limit for scan distribution by default

Release note (sql change): The default value of
`use_soft_limit_for_distribute_scan` session variable has been changed
to `true`. This means that, by default, the soft limit (if available)
will be used to determine whether a scan is "large" and, thus, should be
distributed. For example, with "estimated row count: 100 - 10,000" we'll
use 100 as the estimate to compare against the value of
`distribute_scan_row_count_threshold`.

Author: yuzefovich

pkg/sql/logictest/testdata/logic_test/information_schema

@@ -4162,7 +4162,7 @@ use_cputs_on_non_unique_indexes                                  off
 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                               off
+use_soft_limit_for_distribute_scan                               on
 variable_inequality_lookup_join_enabled                          on
 vector_search_beam_size                                          32
 vector_search_rerank_multiplier                                  50

pkg/sql/logictest/testdata/logic_test/pg_catalog

@@ -3176,7 +3176,7 @@ use_declarative_schema_changer                                   on
 use_improved_routine_dependency_tracking                         on                  NULL      NULL        NULL        string
 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                               off                 NULL      NULL        NULL        string
+use_soft_limit_for_distribute_scan                               on                  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
@@ -3419,7 +3419,7 @@ use_declarative_schema_changer                                   on
 use_improved_routine_dependency_tracking                         on                  NULL  user     NULL      on                  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                               off                 NULL  user     NULL      off                 off
+use_soft_limit_for_distribute_scan                               on                  NULL  user     NULL      on                  on
 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

pkg/sql/logictest/testdata/logic_test/show_source

@@ -253,7 +253,7 @@ use_declarative_schema_changer                                   on
 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                               off
+use_soft_limit_for_distribute_scan                               on
 variable_inequality_lookup_join_enabled                          on
 vector_search_beam_size                                          32
 vector_search_rerank_multiplier                                  50

pkg/sql/vars.go

@@ -751,7 +751,7 @@ var varGen = map[string]sessionVar{
 		Get: func(evalCtx *extendedEvalContext, _ *kv.Txn) (string, error) {
 			return formatBoolAsPostgresSetting(evalCtx.SessionData().UseSoftLimitForDistributeScan), nil
 		},
-		GlobalDefault: globalFalse,
+		GlobalDefault: globalTrue,
 	},
 
 	// CockroachDB extension.