sql: harden recent change about DO block recursion

This commit reduces the max depth of recursion when evaluating routines
with `tail-call-optimization-enabled=false` (recently added in
7b879ef) from 10k to 100. We've just
seen a few cases where TestRandomSyntaxSQLSmith failed because DO block
didn't respect context cancellation within 5s. I've manually tried it
out a few times, and things worked, so my hypothesis is that extremely
deep stacks (that are produced with the TCO disabled) is the root cause
for slow cancellation, so let's just error out sooner.

This commit also brings back the skip of DO blocks in TestComposeCompare
(thinking there is that we should stabilize them in other tests first).

Release note: None

Author: yuzefovich

pkg/compose/compare/compare/compare_test.go

@@ -79,8 +79,13 @@ func TestCompare(t *testing.T) {
 	}
 	configs := map[string]testConfig{
 		"mutators": {
-			setup:           sqlsmith.Setups[sqlsmith.RandTableSetupName],
-			opts:            []sqlsmith.SmitherOption{sqlsmith.CompareMode()},
+			setup: sqlsmith.Setups[sqlsmith.RandTableSetupName],
+			opts: []sqlsmith.SmitherOption{
+				sqlsmith.CompareMode(),
+				// TODO(yuzefovich): perhaps allow DO blocks again after they
+				// have been stabilized in other tests.
+				sqlsmith.DisableDoBlocks(),
+			},
 			ignoreSQLErrors: true,
 			conns: []testConn{
 				{

pkg/sql/routine.go

@@ -163,7 +163,7 @@ func (p *planner) EvalRoutineExpr(
 		if routineDepthValue := ctx.Value(routineDepthKey{}); routineDepthValue != nil {
 			routineDepth = routineDepthValue.(int)
 		}
-		const maxDepth = 10000
+		const maxDepth = 100
 		if routineDepth > maxDepth {
 			return nil, pgerror.Newf(pgcode.ProgramLimitExceeded,
 				"routine reached recursion depth limit: %d (probably infinite loop)", maxDepth)