diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 1de75560..75db969f 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -29,6 +29,7 @@ add_executable(mdbx_test
   utils.h
   append.cc
   ttl.cc
+  nested.cc
   )
 
 set_target_properties(mdbx_test PROPERTIES
diff --git a/test/cases.cc b/test/cases.cc
index 02177140..5442c08d 100644
--- a/test/cases.cc
+++ b/test/cases.cc
@@ -70,6 +70,7 @@ void testcase_setup(const char *casename, actor_params &params,
     configure_actor(last_space_id, ac_try, nullptr, params);
     configure_actor(last_space_id, ac_copy, nullptr, params);
     configure_actor(last_space_id, ac_append, nullptr, params);
+    configure_actor(last_space_id, ac_nested, nullptr, params);
     log_notice("<<< testcase_setup(%s): done", casename);
   } else {
     failure("unknown testcase `%s`", casename);
diff --git a/test/config.h b/test/config.h
index 50e00382..3efba627 100644
--- a/test/config.h
+++ b/test/config.h
@@ -29,7 +29,8 @@ enum actor_testcase {
   ac_try,
   ac_copy,
   ac_append,
-  ac_ttl
+  ac_ttl,
+  ac_nested
 };
 
 enum actor_status {
diff --git a/test/hill.cc b/test/hill.cc
index 89a802ec..9d989095 100644
--- a/test/hill.cc
+++ b/test/hill.cc
@@ -18,7 +18,7 @@ bool testcase_hill::run() {
   int err = db_open__begin__table_create_open_clean(dbi);
   if (unlikely(err != MDBX_SUCCESS)) {
     log_notice("hill: bailout-prepare due '%s'", mdbx_strerror(err));
-    return true;
+    return false;
   }
   speculum.clear();
   speculum_commited.clear();
diff --git a/test/main.cc b/test/main.cc
index e34f914f..4a90605f 100644
--- a/test/main.cc
+++ b/test/main.cc
@@ -361,6 +361,10 @@ int main(int argc, char *const argv[]) {
       configure_actor(last_space_id, ac_ttl, value, params);
       continue;
     }
+    if (config::parse_option(argc, argv, narg, "nested", nullptr)) {
+      configure_actor(last_space_id, ac_nested, value, params);
+      continue;
+    }
     if (config::parse_option(argc, argv, narg, "failfast",
                              global::config::failfast))
       continue;
diff --git a/test/nested.cc b/test/nested.cc
new file mode 100644
index 00000000..e6202464
--- /dev/null
+++ b/test/nested.cc
@@ -0,0 +1,278 @@
+/*
+ * Copyright 2017-2019 Leonid Yuriev <leo@yuriev.ru>
+ * and other libmdbx authors: please see AUTHORS file.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted only as authorized by the OpenLDAP
+ * Public License.
+ *
+ * A copy of this license is available in the file LICENSE in the
+ * top-level directory of the distribution or, alternatively, at
+ * <http://www.OpenLDAP.org/license.html>.
+ */
+
+#include "test.h"
+#include <cmath>
+
+bool testcase_nested::setup() {
+  if (!inherited::setup())
+    return false;
+  int err = db_open__begin__table_create_open_clean(dbi);
+  if (unlikely(err != MDBX_SUCCESS)) {
+    log_notice("nested: bailout-prepare due '%s'", mdbx_strerror(err));
+    return false;
+  }
+
+  keyvalue_maker.setup(config.params, config.actor_id, 0 /* thread_number */);
+  key = keygen::alloc(config.params.keylen_max);
+  data = keygen::alloc(config.params.datalen_max);
+  serial = 0;
+  fifo.clear();
+  speculum.clear();
+  assert(stack.empty());
+  stack.emplace(nullptr, serial, fifo, speculum);
+  return true;
+}
+
+bool testcase_nested::teardown() {
+  while (!stack.empty())
+    pop_txn(true);
+
+  bool ok = true;
+  if (dbi) {
+    if (config.params.drop_table && !mode_readonly()) {
+      txn_begin(false);
+      db_table_drop(dbi);
+      int err = breakable_commit();
+      if (unlikely(err != MDBX_SUCCESS)) {
+        log_notice("nested: bailout-clean due '%s'", mdbx_strerror(err));
+        ok = false;
+      }
+    } else
+      db_table_close(dbi);
+    dbi = 0;
+  }
+  return inherited::teardown() && ok;
+}
+
+static unsigned edge2window(uint64_t edge, unsigned window_max) {
+  const double rnd = u64_to_double1(bleach64(edge));
+  const unsigned window = window_max - std::lrint(std::pow(window_max, rnd));
+  return window;
+}
+
+static unsigned edge2count(uint64_t edge, unsigned count_max) {
+  const double rnd = u64_to_double1(prng64_map1_white(edge));
+  const unsigned count = std::lrint(std::pow(count_max, rnd));
+  return count;
+}
+
+void testcase_nested::push_txn() {
+  MDBX_txn *txn;
+  int err = mdbx_txn_begin(
+      db_guard.get(), txn_guard.get(),
+      prng32() & (MDBX_NOSYNC | MDBX_NOMETASYNC | MDBX_MAPASYNC), &txn);
+  if (unlikely(err != MDBX_SUCCESS))
+    failure_perror("mdbx_txn_begin(nested)", err);
+  stack.emplace(txn, serial, fifo, speculum);
+  std::swap(txn_guard, std::get<0>(stack.top()));
+  log_verbose("begin level#%zu txn, serial %" PRIu64, stack.size(), serial);
+}
+
+bool testcase_nested::pop_txn(bool abort) {
+  assert(txn_guard && !stack.empty());
+  bool should_continue = true;
+  MDBX_txn *txn = txn_guard.release();
+  bool commited = false;
+  if (abort) {
+    log_verbose("abort level#%zu txn, undo serial %" PRIu64 " <- %" PRIu64,
+                stack.size(), serial, std::get<1>(stack.top()));
+    int err = mdbx_txn_abort(txn);
+    if (unlikely(err != MDBX_SUCCESS))
+      failure_perror("mdbx_txn_abort()", err);
+  } else {
+    log_verbose("commit level#%zu txn, nested serial %" PRIu64 " -> %" PRIu64,
+                stack.size(), serial, std::get<1>(stack.top()));
+    int err = mdbx_txn_commit(txn);
+    if (likely(err == MDBX_SUCCESS))
+      commited = true;
+    else {
+      should_continue = false;
+      if (err == MDBX_MAP_FULL && config.params.ignore_dbfull) {
+        err = mdbx_txn_abort(txn);
+        if (unlikely(err != MDBX_SUCCESS && err != MDBX_THREAD_MISMATCH))
+          failure_perror("mdbx_txn_abort()", err);
+      } else
+        failure_perror("mdbx_txn_commit()", err);
+    }
+  }
+
+  std::swap(txn_guard, std::get<0>(stack.top()));
+  if (!commited) {
+    serial = std::get<1>(stack.top());
+    std::swap(fifo, std::get<2>(stack.top()));
+    std::swap(speculum, std::get<3>(stack.top()));
+  }
+  stack.pop();
+  return should_continue;
+}
+
+bool testcase_nested::stochastic_breakable_restart_with_nested(
+    bool force_restart) {
+  log_trace(">> stochastic_breakable_restart_with_nested%s",
+            force_restart ? ": force_restart" : "");
+
+  if (force_restart)
+    while (txn_guard)
+      pop_txn(true);
+
+  bool should_continue = true;
+  while (!stack.empty() &&
+         (flipcoin() || txn_underutilization_x256(txn_guard.get()) < 42))
+    should_continue &= pop_txn();
+
+  if (should_continue)
+    while (stack.empty() ||
+           (is_nested_txn_available() && flipcoin() && stack.size() < 5))
+      push_txn();
+
+  log_trace("<< stochastic_breakable_restart_with_nested: should_continue=%s",
+            should_continue ? "yes" : "no");
+  return should_continue;
+}
+
+bool testcase_nested::trim_tail(unsigned window_width) {
+  if (window_width) {
+    while (fifo.size() > window_width) {
+      uint64_t tail_serial = fifo.back().first;
+      const unsigned tail_count = fifo.back().second;
+      log_trace("nested: pop-tail (serial %" PRIu64 ", count %u)", tail_serial,
+                tail_count);
+      fifo.pop_back();
+      for (unsigned n = 0; n < tail_count; ++n) {
+        log_trace("nested: remove-tail %" PRIu64, tail_serial);
+        generate_pair(tail_serial);
+        int err = remove(key, data);
+        if (unlikely(err != MDBX_SUCCESS)) {
+          if (err == MDBX_MAP_FULL && config.params.ignore_dbfull) {
+            log_notice("nested: tail-bailout due '%s'", mdbx_strerror(err));
+            return false;
+          }
+          failure_perror("mdbx_del(tail)", err);
+        }
+        if (unlikely(!keyvalue_maker.increment(tail_serial, 1)))
+          failure("nested: unexpected key-space overflow on the tail");
+      }
+    }
+  } else {
+    log_trace("nested: purge state");
+    db_table_clear(dbi, txn_guard.get());
+    fifo.clear();
+    speculum.clear();
+  }
+  return true;
+}
+
+bool testcase_nested::grow_head(unsigned head_count) {
+  const unsigned insert_flags = (config.params.table_flags & MDBX_DUPSORT)
+                                    ? MDBX_NODUPDATA
+                                    : MDBX_NODUPDATA | MDBX_NOOVERWRITE;
+retry:
+  fifo.push_front(std::make_pair(serial, head_count));
+  for (unsigned n = 0; n < head_count; ++n) {
+    log_trace("nested: insert-head %" PRIu64, serial);
+    generate_pair(serial);
+    int err = insert(key, data, insert_flags);
+    if (unlikely(err != MDBX_SUCCESS)) {
+      if (err == MDBX_MAP_FULL && config.params.ignore_dbfull) {
+        log_notice("nested: head-insert skip due '%s'", mdbx_strerror(err));
+        head_count = n;
+        stochastic_breakable_restart_with_nested(true);
+        goto retry;
+      }
+      failure_perror("mdbx_put(head)", err);
+    }
+
+    if (unlikely(!keyvalue_maker.increment(serial, 1))) {
+      log_notice("nested: unexpected key-space overflow");
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool testcase_nested::run() {
+  /* LY: тест "эмуляцией time-to-live" с вложенными транзакциями:
+   *  - организуется "скользящее окно", которое каждую транзакцию сдвигается
+   *    вперед вдоль числовой оси.
+   *  - по переднему краю "скользящего окна" записи добавляются в таблицу,
+   *    а по заднему удаляются.
+   *  - количество добавляемых/удаляемых записей псевдослучайно зависит
+   *    от номера транзакции, но с экспоненциальным распределением.
+   *  - размер "скользящего окна" также псевдослучайно зависит от номера
+   *    транзакции с "отрицательным" экспоненциальным распределением
+   *    MAX_WIDTH - exp(rnd(N)), при уменьшении окна сдвигается задний
+   *    край и удаляются записи позади него.
+   *  - групповое добавление данных в начало окна и групповое уделение в конце,
+   *    в половине случаев выполняются во вложенных транзакциях.
+   *  - половина запускаемых вложенных транзакций отменяется, последуюим
+   *    повтором групповой операции.
+   *
+   *  Таким образом имитируется поведение таблицы с TTL: записи стохастически
+   *  добавляются и удаляются, но изредка происходят массивные удаления. */
+
+  /* LY: для параметризации используем подходящие параметры, которые не имеют
+   * здесь смысла в первоначальном значении. */
+  const unsigned window_max_lower = 333;
+  const unsigned count_max_lower = 333;
+
+  const unsigned window_max = (config.params.batch_read > window_max_lower)
+                                  ? config.params.batch_read
+                                  : window_max_lower;
+  const unsigned count_max = (config.params.batch_write > count_max_lower)
+                                 ? config.params.batch_write
+                                 : count_max_lower;
+  log_verbose("nested: using `batch_read` value %u for window_max", window_max);
+  log_verbose("nested: using `batch_write` value %u for count_max", count_max);
+
+  uint64_t seed =
+      prng64_map2_white(config.params.keygen.seed) + config.actor_id;
+
+  while (should_continue()) {
+    const uint64_t salt = prng64_white(seed) /* mdbx_txn_id(txn_guard.get()) */;
+    const unsigned window_width = edge2window(salt, window_max);
+    const unsigned head_count = edge2count(salt, count_max);
+    log_debug("nested: step #%zu (serial %" PRIu64
+              ", window %u, count %u) salt %" PRIu64,
+              nops_completed, serial, window_width, head_count, salt);
+
+    if (!trim_tail(window_width))
+      return false;
+    if (!stochastic_breakable_restart_with_nested()) {
+      log_notice("nested: bailout at commit/restart after tail-trim");
+      return false;
+    }
+    if (!speculum_verify()) {
+      log_notice("nested: bailout after tail-trim");
+      return false;
+    }
+
+    if (!grow_head(head_count))
+      return false;
+    if (!stochastic_breakable_restart_with_nested())
+      log_notice("nested: skip commit/restart after head-grow");
+    if (!speculum_verify()) {
+      log_notice("nested: bailout after head-grow");
+      return false;
+    }
+
+    report(1);
+  }
+
+  while (!stack.empty())
+    pop_txn(false);
+
+  return true;
+}
diff --git a/test/test.cc b/test/test.cc
index 479fdf60..f4fd8a8a 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -37,6 +37,8 @@ const char *testcase2str(const actor_testcase testcase) {
     return "append";
   case ac_ttl:
     return "ttl";
+  case ac_nested:
+    return "nested";
   }
 }
 
@@ -197,6 +199,20 @@ int testcase::breakable_commit() {
   return rc;
 }
 
+unsigned testcase::txn_underutilization_x256(MDBX_txn *txn) const {
+  if (txn) {
+    MDBX_txn_info info;
+    int err = mdbx_txn_info(txn, &info, false);
+    if (unlikely(err != MDBX_SUCCESS))
+      failure_perror("mdbx_txn_info()", err);
+    const size_t left = size_t(info.txn_space_leftover);
+    const size_t total =
+        size_t(info.txn_space_leftover) + size_t(info.txn_space_dirty);
+    return (unsigned)(left / (total >> 8));
+  }
+  return 0;
+}
+
 void testcase::txn_end(bool abort) {
   log_trace(">> txn_end(%s)", abort ? "abort" : "commit");
   assert(txn_guard);
@@ -479,9 +495,9 @@ void testcase::db_table_drop(MDBX_dbi handle) {
   }
 }
 
-void testcase::db_table_clear(MDBX_dbi handle) {
+void testcase::db_table_clear(MDBX_dbi handle, MDBX_txn *txn) {
   log_trace(">> testcase::db_table_clear, handle %u", handle);
-  int rc = mdbx_drop(txn_guard.get(), handle, false);
+  int rc = mdbx_drop(txn ? txn : txn_guard.get(), handle, false);
   if (unlikely(rc != MDBX_SUCCESS))
     failure_perror("mdbx_drop(delete=false)", rc);
   log_trace("<< testcase::db_table_clear");
@@ -549,6 +565,9 @@ bool test_execute(const actor_config &config_const) {
     case ac_ttl:
       test.reset(new testcase_ttl(config, pid));
       break;
+    case ac_nested:
+      test.reset(new testcase_nested(config, pid));
+      break;
     default:
       test.reset(new testcase(config, pid));
       break;
diff --git a/test/test.h b/test/test.h
index b65d51aa..0ca71754 100644
--- a/test/test.h
+++ b/test/test.h
@@ -22,7 +22,10 @@
 #include "osal.h"
 #include "utils.h"
 
+#include <deque>
 #include <set>
+#include <stack>
+#include <tuple>
 
 #ifndef HAVE_cxx17_std_string_view
 #if __cplusplus >= 201703L && __has_include(<string_view>)
@@ -160,6 +163,10 @@ protected:
   static int oom_callback(MDBX_env *env, mdbx_pid_t pid, mdbx_tid_t tid,
                           uint64_t txn, unsigned gap, size_t space, int retry);
 
+  bool is_nested_txn_available() const {
+    return (config.params.mode_flags & MDBX_WRITEMAP) == 0;
+  }
+  void kick_progress(bool active) const;
   void db_prepare();
   void db_open();
   void db_close();
@@ -176,10 +183,11 @@ protected:
   void update_canary(uint64_t increment);
   void checkdata(const char *step, MDBX_dbi handle, MDBX_val key2check,
                  MDBX_val expected_valued);
+  unsigned txn_underutilization_x256(MDBX_txn *txn) const;
 
   MDBX_dbi db_table_open(bool create);
   void db_table_drop(MDBX_dbi handle);
-  void db_table_clear(MDBX_dbi handle);
+  void db_table_clear(MDBX_dbi handle, MDBX_txn *txn = nullptr);
   void db_table_close(MDBX_dbi handle);
   int db_open__begin__table_create_open_clean(MDBX_dbi &dbi);
 
@@ -214,14 +222,13 @@ public:
   virtual bool run() { return true; }
   virtual bool teardown();
   virtual ~testcase() {}
-  void kick_progress(bool active) const;
 };
 
 class testcase_ttl : public testcase {
 public:
   testcase_ttl(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_hill : public testcase {
@@ -238,35 +245,35 @@ class testcase_append : public testcase {
 public:
   testcase_append(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_deadread : public testcase {
 public:
   testcase_deadread(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_deadwrite : public testcase {
 public:
   testcase_deadwrite(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_jitter : public testcase {
 public:
   testcase_jitter(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_try : public testcase {
 public:
   testcase_try(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid) {}
-  bool run();
+  bool run() override;
 };
 
 class testcase_copy : public testcase {
@@ -277,5 +284,28 @@ public:
   testcase_copy(const actor_config &config, const mdbx_pid_t pid)
       : testcase(config, pid),
         copy_pathname(config.params.pathname_db + "-copy") {}
-  bool run();
+  bool run() override;
+};
+
+class testcase_nested : public testcase {
+  using inherited = testcase;
+  using FIFO = std::deque<std::pair<uint64_t, unsigned>>;
+
+  uint64_t serial;
+  FIFO fifo;
+  std::stack<std::tuple<scoped_txn_guard, uint64_t, FIFO, SET>> stack;
+
+  bool trim_tail(unsigned window_width);
+  bool grow_head(unsigned head_count);
+  bool pop_txn(bool abort);
+  bool pop_txn() { return pop_txn(flipcoin_x2()); }
+  void push_txn();
+  bool stochastic_breakable_restart_with_nested(bool force_restart = false);
+
+public:
+  testcase_nested(const actor_config &config, const mdbx_pid_t pid)
+      : testcase(config, pid) {}
+  bool setup() override;
+  bool run() override;
+  bool teardown() override;
 };
diff --git a/test/ttl.cc b/test/ttl.cc
index 5782460d..f7ae4220 100644
--- a/test/ttl.cc
+++ b/test/ttl.cc
@@ -32,7 +32,7 @@ bool testcase_ttl::run() {
   int err = db_open__begin__table_create_open_clean(dbi);
   if (unlikely(err != MDBX_SUCCESS)) {
     log_notice("ttl: bailout-prepare due '%s'", mdbx_strerror(err));
-    return true;
+    return false;
   }
 
   /* LY: тест "эмуляцией time-to-live":
@@ -53,18 +53,8 @@ bool testcase_ttl::run() {
 
   /* LY: для параметризации используем подходящие параметры, которые не имеют
    * здесь смысла в первоначальном значении. */
-  const unsigned window_max_lower =
-#ifdef __APPLE__
-      333;
-#else
-      999;
-#endif
-  const unsigned count_max_lower =
-#ifdef __APPLE__
-      333;
-#else
-      999;
-#endif
+  const unsigned window_max_lower = 333;
+  const unsigned count_max_lower = 333;
 
   const unsigned window_max = (config.params.batch_read > window_max_lower)
                                   ? config.params.batch_read
@@ -86,6 +76,7 @@ bool testcase_ttl::run() {
 
   std::deque<std::pair<uint64_t, unsigned>> fifo;
   uint64_t serial = 0;
+  bool rc = false;
   while (should_continue()) {
     const uint64_t salt = prng64_white(seed) /* mdbx_txn_id(txn_guard.get()) */;
 
@@ -103,7 +94,7 @@ bool testcase_ttl::run() {
                   tail_count);
         fifo.pop_back();
         for (unsigned n = 0; n < tail_count; ++n) {
-          log_trace("ttl: remove-tail %" PRIu64, serial);
+          log_trace("ttl: remove-tail %" PRIu64, tail_serial);
           generate_pair(tail_serial);
           err = mdbx_del(txn_guard.get(), dbi, &key->value, &data->value);
           if (unlikely(err != MDBX_SUCCESS)) {
@@ -157,7 +148,9 @@ bool testcase_ttl::run() {
       serial = fifo.front().first;
       fifo.pop_front();
     }
+
     report(1);
+    rc = true;
   }
 
 bailout:
@@ -169,10 +162,10 @@ bailout:
       err = breakable_commit();
       if (unlikely(err != MDBX_SUCCESS)) {
         log_notice("ttl: bailout-clean due '%s'", mdbx_strerror(err));
-        return true;
+        return false;
       }
     } else
       db_table_close(dbi);
   }
-  return true;
+  return rc;
 }
diff --git a/test/utils.cc b/test/utils.cc
index 4372fcf0..c807d0e5 100644
--- a/test/utils.cc
+++ b/test/utils.cc
@@ -331,6 +331,7 @@ double double_from_upper(uint64_t salt) {
 }
 
 bool flipcoin() { return bleach32((uint32_t)entropy_ticks()) & 1; }
+bool flipcoin_x2() { return (bleach32((uint32_t)entropy_ticks()) & 3) == 0; }
 
 bool jitter(unsigned probability_percent) {
   const uint32_t top = UINT32_MAX - UINT32_MAX % 100;
diff --git a/test/utils.h b/test/utils.h
index cdce1de4..35a54d30 100644
--- a/test/utils.h
+++ b/test/utils.h
@@ -355,5 +355,6 @@ uint64_t prng64(void);
 void prng_fill(void *ptr, size_t bytes);
 
 bool flipcoin();
+bool flipcoin_x2();
 bool jitter(unsigned probability_percent);
 void jitter_delay(bool extra = false);