diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index 45c5b0582..40b476669 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -14,11 +14,11 @@ on:
 
 jobs:
   build:
-    runs-on: 'ubuntu-22.04'
+    runs-on: 'ubuntu-24.04'
     name:  'github pages'
     env:
       BUILD_TYPE:  'Release'
-      PYTHON_VERSION: '3.9'
+      PYTHON_VERSION: '3.12'
     strategy:
       fail-fast: false
     steps:
diff --git a/.github/workflows/keyvi.yml b/.github/workflows/keyvi.yml
index 5388a425a..3d94581c4 100644
--- a/.github/workflows/keyvi.yml
+++ b/.github/workflows/keyvi.yml
@@ -20,7 +20,7 @@ jobs:
       fail-fast: false
       matrix:
         type: ['Release', 'Debug']
-        os: ['macos-latest', 'ubuntu-22.04']
+        os: ['macos-latest', 'ubuntu-24.04']
     steps:
       - name: install Linux deps
         if: runner.os == 'Linux'
@@ -55,4 +55,4 @@ jobs:
       - name: Unit tests
         id: unit_tests
         run: |
-         build/unit_test_all
+         build/unit_test_all -l unit_scope
diff --git a/keyvi/include/keyvi/dictionary/match.h b/keyvi/include/keyvi/dictionary/match.h
index ee80d990d..0fe922107 100644
--- a/keyvi/include/keyvi/dictionary/match.h
+++ b/keyvi/include/keyvi/dictionary/match.h
@@ -59,7 +59,7 @@ namespace dictionary {
 #ifdef Py_PYTHON_H
 class attributes_visitor : public boost::static_visitor<PyObject*> {
  public:
-  PyObject* operator()(int i) const { return PyInt_FromLong(i); }
+  PyObject* operator()(int i) const { return PyLong_FromLong(i); }
 
   PyObject* operator()(double i) const { return PyFloat_FromDouble(i); }
 
diff --git a/keyvi/include/keyvi/index/internal/index_writer_worker.h b/keyvi/include/keyvi/index/internal/index_writer_worker.h
index 12690adfe..ea2f30e2d 100644
--- a/keyvi/include/keyvi/index/internal/index_writer_worker.h
+++ b/keyvi/include/keyvi/index/internal/index_writer_worker.h
@@ -70,10 +70,12 @@ class IndexWriterWorker final {
   using compiler_t = std::shared_ptr<dictionary::JsonDictionaryIndexCompiler>;
   struct IndexPayload {
     explicit IndexPayload(const std::string& index_directory, const keyvi::util::parameters_t& params)
-        : compiler_(),
+        : external_process_ctx_(),
+          compiler_(),
           write_counter_(0),
           segments_(),
-          mutex_(),
+          segments_mutex_(),
+          flush_mutex_(),
           index_directory_(index_directory),
           index_toc_file_(index_directory_ / "index.toc"),
           index_toc_file_part_(index_directory_ / "index.toc.part"),
@@ -88,11 +90,13 @@ class IndexWriterWorker final {
       segments_ = std::make_shared<segment_vec_t>();
     }
 
+    boost::asio::io_context external_process_ctx_;
     compiler_t compiler_;
     std::atomic_size_t write_counter_;
     segments_t segments_;
     std::weak_ptr<segment_vec_t> segments_weak_;
-    std::mutex mutex_;
+    std::mutex segments_mutex_;
+    std::mutex flush_mutex_;
     const boost::filesystem::path index_directory_;
     const boost::filesystem::path index_toc_file_;
     const boost::filesystem::path index_toc_file_part_;
@@ -136,7 +140,7 @@ class IndexWriterWorker final {
     segments_t segments = payload_.segments_weak_.lock();
     if (!segments) {
       TRACE("recreate segments weak ptr");
-      std::unique_lock<std::mutex> lock(payload_.mutex_);
+      std::unique_lock<std::mutex> lock(payload_.segments_mutex_);
       payload_.segments_weak_ = payload_.segments_;
       segments = payload_.segments_;
     }
@@ -205,14 +209,15 @@ class IndexWriterWorker final {
         Compile(&payload);
       });
     } else {
-      std::mutex m;
       std::condition_variable c;
-      std::unique_lock<std::mutex> lock(m);
+      std::unique_lock<std::mutex> lock(payload_.flush_mutex_);
 
-      compiler_active_object_([&m, &c](IndexPayload& payload) {
-        PersistDeletes(&payload);
-        Compile(&payload);
-        std::unique_lock<std::mutex> waitLock(m);
+      compiler_active_object_([&c](IndexPayload& payload) {
+        {
+          PersistDeletes(&payload);
+          Compile(&payload);
+          std::unique_lock<std::mutex> lock(payload.flush_mutex_);
+        }
         c.notify_all();
       });
 
@@ -319,7 +324,7 @@ class IndexWriterWorker final {
 
           // thread-safe swap
           {
-            std::unique_lock<std::mutex> lock(payload_.mutex_);
+            std::unique_lock<std::mutex> lock(payload_.segments_mutex_);
             payload_.segments_.swap(new_segments);
           }
           WriteToc(&payload_);
@@ -390,7 +395,8 @@ class IndexWriterWorker final {
     payload_.merge_jobs_.emplace_back(to_merge, merge_policy_id, p, payload_.settings_);
 
     // force external merge if low on filedescriptors
-    payload_.merge_jobs_.back().Run(payload_.segments_->size() + to_merge.size() + 10 > payload_.max_segments_);
+    payload_.merge_jobs_.back().Run(&payload_.external_process_ctx_,
+                                    payload_.segments_->size() + to_merge.size() + 10 > payload_.max_segments_);
   }
 
   void LoadIndex() {
@@ -466,7 +472,7 @@ class IndexWriterWorker final {
 
     // thread-safe swap
     {
-      std::unique_lock<std::mutex> lock(payload->mutex_);
+      std::unique_lock<std::mutex> lock(payload->segments_mutex_);
       payload->segments_.swap(new_segments);
     }
 
diff --git a/keyvi/include/keyvi/index/internal/merge_job.h b/keyvi/include/keyvi/index/internal/merge_job.h
index 30341ac31..9d2f0a278 100644
--- a/keyvi/include/keyvi/index/internal/merge_job.h
+++ b/keyvi/include/keyvi/index/internal/merge_job.h
@@ -26,7 +26,7 @@
 #include <thread>  // NOLINT
 #include <vector>
 
-#include <boost/process.hpp>
+#include <boost/process/v2/process.hpp>
 
 #include "keyvi/dictionary/dictionary_merger.h"
 #include "keyvi/dictionary/dictionary_types.h"
@@ -78,7 +78,7 @@ class MergeJob final {
   MergeJob& operator=(MergeJob const&) = delete;
   MergeJob(const MergeJob& that) = delete;
 
-  void Run(bool force_external_merge = false) {
+  void Run(boost::asio::io_context* external_process_ctx, bool force_external_merge = false) {
     uint64_t job_size = 0;
 
     for (const segment_t& segment : payload_.segments_) {
@@ -88,7 +88,7 @@ class MergeJob final {
     if (force_external_merge == false && job_size < payload_.settings_.GetSegmentExternalMergeKeyThreshold()) {
       DoInternalMerge();
     } else {
-      DoExternalProcessMerge();
+      DoExternalProcessMerge(external_process_ctx);
     }
   }
 
@@ -128,7 +128,7 @@ class MergeJob final {
  private:
   MergeJobPayload payload_;
   size_t id_;
-  std::shared_ptr<boost::process::child> external_process_;
+  std::shared_ptr<boost::process::v2::process> external_process_;
   std::thread internal_merge_;
 
   void DoInternalMerge() {
@@ -154,7 +154,7 @@ class MergeJob final {
     });
   }
 
-  void DoExternalProcessMerge() {
+  void DoExternalProcessMerge(boost::asio::io_context* external_process_ctx) {
     payload_.start_time_ = std::chrono::system_clock::now();
 
     std::vector<std::string> args;
@@ -169,7 +169,8 @@ class MergeJob final {
     args.push_back("-o");
     args.push_back(payload_.output_filename_.string());
 
-    external_process_.reset(new boost::process::child(payload_.settings_.GetKeyviMergerBin(), args));
+    external_process_.reset(
+        new boost::process::v2::process(*external_process_ctx, payload_.settings_.GetKeyviMergerBin(), args));
   }
 
   bool TryFinalizeMerge() {
@@ -177,6 +178,8 @@ class MergeJob final {
       if (!external_process_->running()) {
         payload_.exit_code_ = external_process_->exit_code();
         payload_.process_finished_ = true;
+        // free the process early, closes internal file descriptor
+        external_process_.reset();
         return true;
       }
     } else if (internal_merge_.joinable()) {
@@ -192,6 +195,8 @@ class MergeJob final {
     if (external_process_) {
       external_process_->wait();
       payload_.exit_code_ = external_process_->exit_code();
+      // free the process early, closes internal file descriptor
+      external_process_.reset();
     } else {
       internal_merge_.join();
       // exit code set by merge thread
diff --git a/keyvi/tests/keyvi/index/index_limits_test.cpp b/keyvi/tests/keyvi/index/index_limits_test.cpp
index 33a54c121..a41ee501f 100644
--- a/keyvi/tests/keyvi/index/index_limits_test.cpp
+++ b/keyvi/tests/keyvi/index/index_limits_test.cpp
@@ -28,6 +28,8 @@
 #else
 #include <sys/resource.h>
 
+#include <string>
+
 #include <boost/filesystem.hpp>
 #include <boost/test/unit_test.hpp>
 
@@ -63,7 +65,7 @@ BOOST_AUTO_TEST_CASE(filedescriptor_limit) {
   using boost::filesystem::temp_directory_path;
   using boost::filesystem::unique_path;
 
-  size_t old_limit = limit_filedescriptors(20);
+  size_t old_limit = limit_filedescriptors(40);
 
   auto tmp_path = temp_directory_path();
   tmp_path /= unique_path("index-limits-test-temp-index-%%%%-%%%%-%%%%-%%%%");
@@ -85,7 +87,7 @@ BOOST_AUTO_TEST_CASE(filedescriptor_limit) {
   boost::filesystem::remove_all(tmp_path);
 
   size_t increased_file_descriptors = keyvi::util::OsUtils::TryIncreaseFileDescriptors();
-  BOOST_CHECK(increased_file_descriptors > 20);
+  BOOST_CHECK(increased_file_descriptors > 40);
 
   limit_filedescriptors(old_limit);
 }
diff --git a/keyvi/tests/keyvi/index/internal/merge_job_test.cpp b/keyvi/tests/keyvi/index/internal/merge_job_test.cpp
index b2b91b227..3afab1601 100644
--- a/keyvi/tests/keyvi/index/internal/merge_job_test.cpp
+++ b/keyvi/tests/keyvi/index/internal/merge_job_test.cpp
@@ -24,7 +24,9 @@
  */
 
 #include <chrono>  // NOLINT
+#include <string>
 #include <thread>  // NOLINT
+#include <vector>
 
 #include <boost/test/unit_test.hpp>
 
@@ -51,6 +53,8 @@ namespace internal {
 BOOST_AUTO_TEST_SUITE(MergeJobTests)
 
 BOOST_AUTO_TEST_CASE(basic_merge) {
+  boost::asio::io_context external_process_ctx;
+
   std::vector<std::pair<std::string, std::string>> test_data = {
       {"abc", "{a:1}"}, {"abbc", "{b:2}"}, {"abbcd", "{c:3}"}, {"abcde", "{a:1}"}, {"abdd", "{b:2}"}, {"bba", "{c:3}"},
   };
@@ -70,7 +74,7 @@ BOOST_AUTO_TEST_CASE(basic_merge) {
   boost::filesystem::path p("merged.kv");
   IndexSettings settings({{KEYVIMERGER_BIN, get_keyvimerger_bin()}});
   MergeJob m({w1, w2}, 0, p, settings);
-  m.Run();
+  m.Run(&external_process_ctx);
 
   int retry = 100;
   while (retry > 0) {
diff --git a/python/src/addons/JsonVector.pyx b/python/src/addons/JsonVector.pyx
index 33c582c9d..64a01a0b0 100644
--- a/python/src/addons/JsonVector.pyx
+++ b/python/src/addons/JsonVector.pyx
@@ -1,7 +1,7 @@
 
 
     def __getitem__(self,  index ):
-        assert isinstance(index, (int, long)), 'arg index wrong type'
+        assert isinstance(index, (int, int)), 'arg index wrong type'
 
         cdef libcpp_utf8_string _r = self.inst.get().Get((<size_t>index))
         py_result = json.loads(_r.decode('utf-8'))