roachtest: avoid known problematic pattern in sqlsmith

We are aware of one query pattern where sqlsmith roachtest might time out
(runtime assertions enabled AND one of the system columns that requires
MVCC decoding is requested). This is unfortunate but expected behavior
that we don't plan on improving on, so let's avoid generating this query
pattern.

Release note: None

Author: yuzefovich

pkg/cmd/roachtest/tests/sqlsmith.go

@@ -18,6 +18,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/cluster"
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/option"
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/registry"
+	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/roachtestutil"
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/spec"
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/test"
 	"github.com/cockroachdb/cockroach/pkg/internal/sqlsmith"
@@ -184,22 +185,27 @@ WITH into_db = 'defaultdb';
 						}
 					}()
 
-					stmt = smither.Generate()
-					if stmt == "" {
-						// If an empty statement is generated, then ignore it.
-						done <- errors.Newf("Empty statement returned by generate")
-						return nil
+					for {
+						stmt = smither.Generate()
+						if stmt == "" {
+							// If an empty statement is generated, then ignore it.
+							done <- errors.Newf("Empty statement returned by generate")
+							return nil
+						}
+						if !expectedToTimeout(t, stmt) {
+							break
+						}
 					}
 
 					// TODO(yuzefovich): investigate why using the context with
 					// a timeout results in poisoning the connection (#101208).
 					_, err := conn.Exec(stmt)
 					if err == nil {
 						logStmt(stmt)
-						stmt = "EXPLAIN " + stmt
-						_, err = conn.Exec(stmt)
+						explainStmt := "EXPLAIN " + stmt
+						_, err = conn.Exec(explainStmt)
 						if err == nil {
-							logStmt(stmt)
+							logStmt(explainStmt)
 						}
 					}
 					done <- err
@@ -329,6 +335,27 @@ WITH into_db = 'defaultdb';
 	register("seed-multi-region", "multi-region")
 }
 
+// expectedToTimeout returns whether the given stmt is likely to timeout due to
+// expected edge case behavior.
+func expectedToTimeout(t test.Test, stmt string) bool {
+	// The only known scenario right now (see #157971) is when we have runtime
+	// assertions enabled AND the query uses a system column that requires MVCC
+	// decoding.
+	if !roachtestutil.UsingRuntimeAssertions(t) {
+		return false
+	}
+	for _, sysCol := range []string{
+		"crdb_internal_mvcc_timestamp",
+		"crdb_internal_origin_id",
+		"crdb_internal_origin_timestamp",
+	} {
+		if strings.Contains(stmt, sysCol) {
+			return true
+		}
+	}
+	return false
+}
+
 // setupMultiRegionDatabase is used to set up a multi-region database.
 func setupMultiRegionDatabase(t test.Test, conn *gosql.DB, rnd *rand.Rand, logStmt func(string)) {
 	t.Helper()