tweak search in fz and opb competition mode

ortools/flatzinc/cp_model_fz_solver.cc

@@ -47,6 +47,8 @@
 
 ABSL_FLAG(int64_t, fz_int_max, int64_t{1} << 40,
           "Default max value for unbounded integer variables.");
+ABSL_FLAG(bool, force_interleave_search, false,
+          "If true, enable interleaved workers when num_workers is 1.");
 
 namespace operations_research {
 namespace sat {
@@ -1683,7 +1685,8 @@ void SolveFzWithCpModelProto(const fz::Model& fz_model,
     m.parameters.set_keep_all_feasible_solutions_in_presolve(true);
   } else if (num_workers == 1 && p.use_free_search) {  // Free search.
     m.parameters.set_search_branching(SatParameters::AUTOMATIC_SEARCH);
-    if (!p.search_all_solutions && p.ortools_mode) {
+    if (!p.search_all_solutions &&
+        (absl::GetFlag(FLAGS_force_interleave_search) || p.ortools_mode)) {
       m.parameters.set_interleave_search(true);
       m.parameters.set_use_rins_lns(false);
       m.parameters.add_subsolvers("default_lp");

ortools/flatzinc/fz.cc

@@ -28,6 +28,7 @@
 
 #include "absl/flags/flag.h"
 #include "absl/log/check.h"
+
 #include "absl/log/initialize.h"
 #include "absl/log/log.h"
 #include "absl/strings/match.h"

ortools/sat/sat_runner.cc

@@ -222,6 +222,12 @@ bool LoadProblem(const std::string& filename, absl::string_view hint_file,
     if (absl::GetFlag(FLAGS_force_interleave_search)) {
       SetInterleavedWorkers(parameters);
     }
+    if (parameters->num_workers() >= 2 && parameters->num_workers() <= 15) {
+      // Works better without symmetries in search
+      // TODO(user): Investigate.
+      parameters->add_ignore_subsolvers("max_lp_sym");
+      parameters->add_extra_subsolvers("max_lp");
+    }
   } else if (absl::EndsWith(filename, ".cnf") ||
              absl::EndsWith(filename, ".cnf.xz") ||
              absl::EndsWith(filename, ".cnf.gz") ||