diff --git a/tools/db_crashtest.py b/tools/db_crashtest.py
index 90fde4a30..449d85427 100644
--- a/tools/db_crashtest.py
+++ b/tools/db_crashtest.py
@@ -24,6 +24,7 @@ default_params = {
     "disable_data_sync": 0,
     "disable_wal": 0,
     "filter_deletes": lambda: random.randint(0, 1),
+    "allow_concurrent_memtable_write": lambda: random.randint(0, 1),
     "iterpercent": 10,
     "max_background_compactions": 20,
     "max_bytes_for_level_base": 10485760,
@@ -85,6 +86,7 @@ simple_default_params = {
     "disable_data_sync": 0,
     "disable_wal": 0,
     "filter_deletes": lambda: random.randint(0, 1),
+    "allow_concurrent_memtable_write": lambda: random.randint(0, 1),
     "iterpercent": 10,
     "max_background_compactions": 1,
     "max_bytes_for_level_base": 67108864,
@@ -126,6 +128,15 @@ whitebox_simple_default_params = {
 }
 
 
+def finalize_and_sanitize(src_params):
+    dest_params = dict([(k,  v() if callable(v) else v)
+                        for (k, v) in src_params.items()])
+    # --allow_concurrent_memtable_write with --filter_deletes is not supported.
+    if dest_params.get("allow_concurrent_memtable_write", 1) == 1:
+        dest_params["filter_deletes"] = 0
+    return dest_params
+
+
 def gen_cmd_params(args):
     params = {}
 
@@ -151,8 +162,8 @@ def gen_cmd_params(args):
 
 def gen_cmd(params):
     cmd = './db_stress ' + ' '.join(
-        '--{0}={1}'.format(k, v() if callable(v) else v)
-        for k, v in params.items()
+        '--{0}={1}'.format(k, v)
+        for k, v in finalize_and_sanitize(params).items()
         if k not in set(['test_type', 'simple', 'duration', 'interval'])
         and v is not None)
     return cmd
diff --git a/tools/db_stress.cc b/tools/db_stress.cc
index 102803862..10193a182 100644
--- a/tools/db_stress.cc
+++ b/tools/db_stress.cc
@@ -230,6 +230,13 @@ DEFINE_int64(cache_size, 2LL * KB * KB * KB,
 DEFINE_uint64(subcompactions, 1,
              "Maximum number of subcompactions to divide L0-L1 compactions "
              "into.");
+
+DEFINE_bool(allow_concurrent_memtable_write, true,
+            "Allow multi-writers to update mem tables in parallel.");
+
+DEFINE_bool(enable_write_thread_adaptive_yield, true,
+            "Use a yielding spin loop for brief writer thread waits.");
+
 static const bool FLAGS_subcompactions_dummy __attribute__((unused)) =
     RegisterFlagValidator(&FLAGS_subcompactions, &ValidateUint32Range);
 
@@ -1997,6 +2004,10 @@ class StressTest {
     options_.filter_deletes = FLAGS_filter_deletes;
     options_.inplace_update_support = FLAGS_in_place_update;
     options_.max_subcompactions = static_cast<uint32_t>(FLAGS_subcompactions);
+    options_.allow_concurrent_memtable_write =
+        FLAGS_allow_concurrent_memtable_write;
+    options_.enable_write_thread_adaptive_yield =
+        FLAGS_enable_write_thread_adaptive_yield;
     if ((FLAGS_prefix_size == 0) == (FLAGS_rep_factory == kHashSkipList)) {
       fprintf(stderr,
             "prefix_size should be non-zero iff memtablerep == prefix_hash\n");