opt: set default optimizer_span_limit to 131072

Set the default value of the `optimizer_span_limit` session variable to
2^17 (131072) instead of 0 (no limit). This provides a reasonable upper
bound on the number of spans the optimizer will produce, preventing
pathological cases where large cross-products of IN sets produce
excessive spans.

Informs: #167620

Release note (sql change): The session variable `optimizer_span_limit`
now defaults to 131072. This bounds the number of spans the optimizer
will allow in constrained index scans generated during query
optimization. Queries that would exceed this limit will use fewer looser
spans with remaining filters instead. Set to 0 to disable the limit.

Co-Authored-By: roachdev-claude <roachdev-claude-bot@cockroachlabs.com>

Author: michae2

pkg/sql/logictest/testdata/logic_test/information_schema

@@ -3919,7 +3919,7 @@ optimizer_prefer_bounded_cardinality                             on
 optimizer_prove_implication_with_virtual_computed_columns        on
 optimizer_push_limit_into_project_filtered_scan                  on
 optimizer_push_offset_into_index_join                            on
-optimizer_span_limit                                             0
+optimizer_span_limit                                             131072
 optimizer_use_conditional_hoist_fix                              on
 optimizer_use_delete_range_fast_path                             on
 optimizer_use_exists_filter_hoist_rule                           on

pkg/sql/logictest/testdata/logic_test/pg_catalog

@@ -3320,7 +3320,7 @@ optimizer_prefer_bounded_cardinality                             on
 optimizer_prove_implication_with_virtual_computed_columns        on                  NULL      NULL        NULL        string
 optimizer_push_limit_into_project_filtered_scan                  on                  NULL      NULL        NULL        string
 optimizer_push_offset_into_index_join                            on                  NULL      NULL        NULL        string
-optimizer_span_limit                                             0                   NULL      NULL        NULL        string
+optimizer_span_limit                                             131072              NULL      NULL        NULL        string
 optimizer_use_conditional_hoist_fix                              on                  NULL      NULL        NULL        string
 optimizer_use_delete_range_fast_path                             on                  NULL      NULL        NULL        string
 optimizer_use_exists_filter_hoist_rule                           on                  NULL      NULL        NULL        string
@@ -3580,7 +3580,7 @@ optimizer_prefer_bounded_cardinality                             on
 optimizer_prove_implication_with_virtual_computed_columns        on                  NULL  user     NULL      on                  on
 optimizer_push_limit_into_project_filtered_scan                  on                  NULL  user     NULL      on                  on
 optimizer_push_offset_into_index_join                            on                  NULL  user     NULL      on                  on
-optimizer_span_limit                                             0                   NULL  user     NULL      0                   0
+optimizer_span_limit                                             131072              NULL  user     NULL      131072              131072
 optimizer_use_conditional_hoist_fix                              on                  NULL  user     NULL      on                  on
 optimizer_use_delete_range_fast_path                             on                  NULL  user     NULL      on                  on
 optimizer_use_exists_filter_hoist_rule                           on                  NULL  user     NULL      on                  on

pkg/sql/logictest/testdata/logic_test/show_source

@@ -168,7 +168,7 @@ optimizer_prefer_bounded_cardinality                             on
 optimizer_prove_implication_with_virtual_computed_columns        on                  Controls whether the optimizer should use virtual computed columns to prove partial index implication.
 optimizer_push_limit_into_project_filtered_scan                  on                  Controls whether the optimizer should push limit expressions into projects of filtered scans.
 optimizer_push_offset_into_index_join                            on                  Controls whether the optimizer should push offset expressions into index joins.
-optimizer_span_limit                                             0                   Sets the maximum number of constraint spans allowed in a scan during query optimization. 0 means no limit.
+optimizer_span_limit                                             131072              Sets the maximum number of constraint spans allowed in a scan during query optimization. 0 means no limit.
 optimizer_use_conditional_hoist_fix                              on                  Prevents the optimizer from hoisting volatile expressions that are conditionally executed by CASE, COALESCE, or IFERR expressions.
 optimizer_use_delete_range_fast_path                             on                  Controls whether the optimizer uses the fast path for DELETE operations using range deletions.
 optimizer_use_exists_filter_hoist_rule                           on                  Controls whether the optimizer hoists filters out of EXISTS subqueries.

pkg/sql/sessiondatapb/local_only_session_data.proto

@@ -814,7 +814,7 @@ message LocalOnlySessionData {
   // (show CRDB syntax explicitly).
   string pg_dump_compatibility = 206;
   // OptimizerSpanLimit sets the maximum number of constraint spans allowed in
-  // a scan during query optimization. 0 means no limit.
+  // a scan during query optimization. 0 means no limit. Default: 131072.
   int32 optimizer_span_limit = 207;
 
   ///////////////////////////////////////////////////////////////////////////

pkg/sql/vars.go

@@ -3016,7 +3016,7 @@ var varGen = map[string]sessionVar{
 			return strconv.FormatInt(int64(evalCtx.SessionData().OptimizerSpanLimit), 10), nil
 		},
 		GlobalDefault: func(_ *settings.Values) string {
-			return "0"
+			return "131072"
 		},
 	},