sql: override StmtTimeout to 0 for background jobs

For background jobs and schema changes, our Internal
Executor inherits from cluster settings. If a statement
timeout is set cluster-wide, then background jobs will
respect this -- which does not make much sense; thus,
this patch overrides the StmtTimeout to 0s for background
jobs.

Fixes: cockroachdb#126261
Release note (bug fix): Background jobs no longer respect
a statement timeout.

pkg/sql/internal.go

@@ -95,6 +95,7 @@ func NewInternalSessionData(
 	sd.SearchPath = sessiondata.DefaultSearchPathForUser(username.NodeUserName())
 	sd.SequenceState = sessiondata.NewSequenceState()
 	sd.Location = time.UTC
+	sd.StmtTimeout = 0
 	return sd
 }
 

pkg/sql/opt/exec/execbuilder/testdata/execute_internally_builtin

@@ -215,3 +215,37 @@ root
 
 statement ok
 SELECT crdb_internal.execute_internally('EXPLAIN ANALYZE SELECT 1;');
+
+# Ensure that StmtTimeout for a session-independent IE cannot be overriden.
+subtest stmt_timeout
+
+statement ok
+SET CLUSTER SETTING sql.defaults.statement_timeout = '36000000ms';
+
+statement ok
+SET statement_timeout = '39600000ms';
+
+query T
+SELECT crdb_internal.execute_internally('SHOW statement_timeout;');
+----
+0
+
+# Ensure that a session-bound IE still inherits from session vars, if available;
+# otherwise, it inherits from the cluster setting.
+query T
+SELECT crdb_internal.execute_internally('SHOW statement_timeout;', true);
+----
+39600000
+
+statement ok
+RESET statement_timeout;
+
+query T
+SELECT crdb_internal.execute_internally('SHOW statement_timeout;', true);
+----
+36000000
+
+statement ok
+RESET CLUSTER SETTING sql.defaults.statement_timeout;
+
+subtest end