diff --git a/rocksdb/_rocksdb.pyx b/rocksdb/_rocksdb.pyx
index 6eab1fa..39ae114 100644
--- a/rocksdb/_rocksdb.pyx
+++ b/rocksdb/_rocksdb.pyx
@@ -62,13 +62,6 @@ import weakref
 cdef extern from "cpp/utils.hpp" namespace "py_rocks":
     cdef const Slice* vector_data(vector[Slice]&)
 
-# Prepare python for threaded usage.
-# Python callbacks (merge, comparator)
-# could be executed in a rocksdb background thread (eg. compaction).
-cdef extern from "Python.h":
-    void PyEval_InitThreads()
-PyEval_InitThreads()
-
 ## Here comes the stuff to wrap the status to exception
 cdef check_status(const Status& st):
     if st.ok():
@@ -100,19 +93,20 @@ cdef check_status(const Status& st):
 
 
 cdef string bytes_to_string(path) except *:
-    return string(PyBytes_AsString(path), PyBytes_Size(path))
+    return string(PyBytes_AsString(path), <size_t> PyBytes_Size(path))
 
 cdef string_to_bytes(string ob):
-    return PyBytes_FromStringAndSize(ob.c_str(), ob.size())
+    return PyBytes_FromStringAndSize(ob.c_str(), <Py_ssize_t> ob.size())
 
 cdef Slice bytes_to_slice(ob) except *:
-    return Slice(PyBytes_AsString(ob), PyBytes_Size(ob))
+    return Slice(PyBytes_AsString(ob), <size_t> PyBytes_Size(ob))
 
-cdef Slice* bytes_to_new_slice(ob) except *:
-    return new Slice(PyBytes_AsString(ob), PyBytes_Size(ob))
+# XXX: unused
+#cdef Slice* bytes_to_new_slice(ob) except *:
+#    return new Slice(PyBytes_AsString(ob), <size_t> PyBytes_Size(ob))
 
 cdef slice_to_bytes(Slice sl):
-    return PyBytes_FromStringAndSize(sl.data(), sl.size())
+    return PyBytes_FromStringAndSize(sl.data(), <Py_ssize_t> sl.size())
 
 ## only for filsystem paths
 cdef string path_to_string(object path) except *:
@@ -126,7 +120,7 @@ cdef string path_to_string(object path) except *:
 
 cdef object string_to_path(string path):
     fs_encoding = sys.getfilesystemencoding().encode('ascii')
-    return PyUnicode_Decode(path.c_str(), path.size(), fs_encoding, "replace")
+    return PyUnicode_Decode(path.c_str(), <Py_ssize_t> path.size(), fs_encoding, "replace")
 
 ## Here comes the stuff for the comparator
 @cython.internal
@@ -311,7 +305,7 @@ cdef cpp_bool full_merge_callback(
         ret = (<object>ctx).full_merge(
             slice_to_bytes(key),
             py_existing_value,
-            [string_to_bytes(op_list[i]) for i in range(op_list.size())])
+            [string_to_bytes(op_list[i]) for i in range(<size_t> op_list.size())])
 
         if ret[0]:
             new_value.assign(bytes_to_string(ret[1]))
@@ -524,7 +518,7 @@ cdef class BlockBasedTableFactory(PyTableFactory):
                 table_options.cache_index_and_filter_blocks = False
 
         if format_version is not None:
-            table_options.format_version = format_version
+            table_options.format_version = <uint32_t> format_version
 
         self.factory.reset(table_factory.NewBlockBasedTableFactory(table_options))
 
@@ -641,7 +635,7 @@ cdef class _ColumnFamilyHandle:
 
     @property
     def id(self):
-        return self.handle.GetID()
+        return <int> self.handle.GetID()
 
     @property
     def weakref(self):
@@ -1378,7 +1372,7 @@ cdef class WriteBatch(object):
         return string_to_bytes(self.batch.Data())
 
     def count(self):
-        return self.batch.Count()
+        return <int> self.batch.Count()
 
     def __iter__(self):
         return WriteBatchIterator(self)
@@ -1706,7 +1700,7 @@ cdef class DB(object):
             keys = list(dict.fromkeys(keys))
 
         cdef vector[string] values
-        values.resize(len(keys))
+        values.resize(<size_t> len(keys))
 
         cdef db.ColumnFamilyHandle* cf_handle
         cdef vector[db.ColumnFamilyHandle*] cf_handles
@@ -1734,7 +1728,8 @@ cdef class DB(object):
         cdef dict ret_dict = {}
         cdef list ret_list = []
         if as_dict:
-            for index in range(len(keys)):
+            for index in range(<size_t> len(keys)):
+                index = <size_t> index
                 if res[index].ok():
                     ret_dict[keys[index]] = string_to_bytes(values[index])
                 elif res[index].IsNotFound():
@@ -1744,7 +1739,8 @@ cdef class DB(object):
 
             return ret_dict
         else:
-            for index in range(len(keys)):
+            for index in range(<size_t> len(keys)):
+                index = <size_t> index
                 if res[index].ok():
                     ret_list.append(string_to_bytes(values[index]))
                 elif res[index].IsNotFound():
@@ -1842,7 +1838,7 @@ cdef class DB(object):
 
     def iterskeys(self, column_families, *args, **kwargs):
         cdef vector[db.Iterator*] iters
-        iters.resize(len(column_families))
+        iters.resize(<size_t> len(column_families))
         cdef options.ReadOptions opts
         cdef db.Iterator* it_ptr
         cdef KeysIterator it
@@ -1867,7 +1863,7 @@ cdef class DB(object):
 
     def itersvalues(self, column_families, *args, **kwargs):
         cdef vector[db.Iterator*] iters
-        iters.resize(len(column_families))
+        iters.resize(<size_t> len(column_families))
         cdef options.ReadOptions opts
         cdef db.Iterator* it_ptr
         cdef ValuesIterator it
@@ -1891,7 +1887,7 @@ cdef class DB(object):
 
     def iterskeys(self, column_families, *args, **kwargs):
         cdef vector[db.Iterator*] iters
-        iters.resize(len(column_families))
+        iters.resize(<size_t> len(column_families))
         cdef options.ReadOptions opts
         cdef db.Iterator* it_ptr
         cdef ItemsIterator it
diff --git a/rocksdb/comparator.pxd b/rocksdb/comparator.pxd
index f6bb467..2aa34b2 100644
--- a/rocksdb/comparator.pxd
+++ b/rocksdb/comparator.pxd
@@ -8,7 +8,7 @@ cdef extern from "rocksdb/comparator.h" namespace "rocksdb":
         const char* Name()
         int Compare(const Slice&, const Slice&) const
 
-    cdef extern const Comparator* BytewiseComparator() nogil except +
+    cdef extern const Comparator* BytewiseComparator() except + nogil
 
 ctypedef int (*compare_func)(
     void*,
@@ -19,5 +19,5 @@ ctypedef int (*compare_func)(
 
 cdef extern from "cpp/comparator_wrapper.hpp" namespace "py_rocks":
     cdef cppclass ComparatorWrapper:
-        ComparatorWrapper(string, void*, compare_func) nogil except +
-        void set_info_log(shared_ptr[Logger]) nogil except+
+        ComparatorWrapper(string, void*, compare_func) except + nogil
+        void set_info_log(shared_ptr[Logger]) except+ nogil
diff --git a/rocksdb/db.pxd b/rocksdb/db.pxd
index 40151ba..262f917 100644
--- a/rocksdb/db.pxd
+++ b/rocksdb/db.pxd
@@ -11,18 +11,18 @@ from .iterator cimport Iterator
 
 cdef extern from "rocksdb/write_batch.h" namespace "rocksdb":
     cdef cppclass WriteBatch:
-        WriteBatch() nogil except+
-        WriteBatch(string) nogil except+
-        void Put(const Slice&, const Slice&) nogil except+
-        void Put(ColumnFamilyHandle*, const Slice&, const Slice&) nogil except+
-        void Merge(const Slice&, const Slice&) nogil except+
-        void Merge(ColumnFamilyHandle*, const Slice&, const Slice&) nogil except+
-        void Delete(const Slice&) nogil except+
-        void Delete(ColumnFamilyHandle*, const Slice&) nogil except+
-        void PutLogData(const Slice&) nogil except+
-        void Clear() nogil except+
-        const string& Data() nogil except+
-        int Count() nogil except+
+        WriteBatch() except+ nogil
+        WriteBatch(string) except+ nogil
+        void Put(const Slice&, const Slice&) except+ nogil
+        void Put(ColumnFamilyHandle*, const Slice&, const Slice&) except+ nogil
+        void Merge(const Slice&, const Slice&) except+ nogil
+        void Merge(ColumnFamilyHandle*, const Slice&, const Slice&) except+ nogil
+        void Delete(const Slice&) except+ nogil
+        void Delete(ColumnFamilyHandle*, const Slice&) except+ nogil
+        void PutLogData(const Slice&) except+ nogil
+        void Clear() except+ nogil
+        const string& Data() except+ nogil
+        uint32_t Count() except+ nogil
 
 cdef extern from "cpp/write_batch_iter_helper.hpp" namespace "py_rocks":
     cdef enum BatchItemOp "RecordItemsHandler::Optype":
@@ -81,95 +81,95 @@ cdef extern from "rocksdb/db.h" namespace "rocksdb":
             const options.WriteOptions&,
             ColumnFamilyHandle*,
             const Slice&,
-            const Slice&) nogil except+
+            const Slice&) except+ nogil
 
         Status Delete(
             const options.WriteOptions&,
             ColumnFamilyHandle*,
-            const Slice&) nogil except+
+            const Slice&) except+ nogil
 
         Status Merge(
             const options.WriteOptions&,
             ColumnFamilyHandle*,
             const Slice&,
-            const Slice&) nogil except+
+            const Slice&) except+ nogil
 
         Status Write(
             const options.WriteOptions&,
-            WriteBatch*) nogil except+
+            WriteBatch*) except+ nogil
 
         Status Get(
             const options.ReadOptions&,
             ColumnFamilyHandle*,
             const Slice&,
-            string*) nogil except+
+            string*) except+ nogil
 
         vector[Status] MultiGet(
             const options.ReadOptions&,
             const vector[ColumnFamilyHandle*]&,
             const vector[Slice]&,
-            vector[string]*) nogil except+
+            vector[string]*) except+ nogil
 
         cpp_bool KeyMayExist(
             const options.ReadOptions&,
             ColumnFamilyHandle*,
             Slice&,
             string*,
-            cpp_bool*) nogil except+
+            cpp_bool*) except+ nogil
 
         cpp_bool KeyMayExist(
             const options.ReadOptions&,
             ColumnFamilyHandle*,
             Slice&,
-            string*) nogil except+
+            string*) except+ nogil
 
         Iterator* NewIterator(
             const options.ReadOptions&,
-            ColumnFamilyHandle*) nogil except+
+            ColumnFamilyHandle*) except+ nogil
 
         void NewIterators(
             const options.ReadOptions&,
             vector[ColumnFamilyHandle*]&,
-            vector[Iterator*]*) nogil except+
+            vector[Iterator*]*) except+ nogil
 
-        const Snapshot* GetSnapshot() nogil except+
+        const Snapshot* GetSnapshot() except+ nogil
 
-        void ReleaseSnapshot(const Snapshot*) nogil except+
+        void ReleaseSnapshot(const Snapshot*) except+ nogil
 
         cpp_bool GetProperty(
             ColumnFamilyHandle*,
             const Slice&,
-            string*) nogil except+
+            string*) except+ nogil
 
         void GetApproximateSizes(
             ColumnFamilyHandle*,
             const Range*
             int,
-            uint64_t*) nogil except+
+            uint64_t*) except+ nogil
 
         Status CompactRange(
             const options.CompactRangeOptions&,
             ColumnFamilyHandle*,
             const Slice*,
-            const Slice*) nogil except+
+            const Slice*) except+ nogil
 
         Status CreateColumnFamily(
             const options.ColumnFamilyOptions&,
             const string&,
-            ColumnFamilyHandle**) nogil except+
+            ColumnFamilyHandle**) except+ nogil
 
         Status DropColumnFamily(
-            ColumnFamilyHandle*) nogil except+
-
-        int NumberLevels(ColumnFamilyHandle*) nogil except+
-        int MaxMemCompactionLevel(ColumnFamilyHandle*) nogil except+
-        int Level0StopWriteTrigger(ColumnFamilyHandle*) nogil except+
-        const string& GetName() nogil except+
-        const options.Options& GetOptions(ColumnFamilyHandle*) nogil except+
-        Status Flush(const options.FlushOptions&, ColumnFamilyHandle*) nogil except+
-        Status DisableFileDeletions() nogil except+
-        Status EnableFileDeletions() nogil except+
-        Status Close() nogil except+
+            ColumnFamilyHandle*) except+ nogil
+
+        int NumberLevels(ColumnFamilyHandle*) except+ nogil
+        int MaxMemCompactionLevel(ColumnFamilyHandle*) except+ nogil
+        int Level0StopWriteTrigger(ColumnFamilyHandle*) except+ nogil
+        const string& GetName() except+ nogil
+        const options.Options& GetOptions(ColumnFamilyHandle*) except+ nogil
+        Status Flush(const options.FlushOptions&, ColumnFamilyHandle*) except+ nogil
+        Status DisableFileDeletions() except+ nogil
+        Status EnableFileDeletions() except+ nogil
+        Status Close() except+ nogil
 
         # TODO: Status GetSortedWalFiles(VectorLogPtr& files)
         # TODO: SequenceNumber GetLatestSequenceNumber()
@@ -177,9 +177,9 @@ cdef extern from "rocksdb/db.h" namespace "rocksdb":
                   # SequenceNumber seq_number,
                   # unique_ptr[TransactionLogIterator]*)
 
-        Status DeleteFile(string) nogil except+
-        void GetLiveFilesMetaData(vector[LiveFileMetaData]*) nogil except+
-        void GetColumnFamilyMetaData(ColumnFamilyHandle*, ColumnFamilyMetaData*) nogil except+
+        Status DeleteFile(string) except+ nogil
+        void GetLiveFilesMetaData(vector[LiveFileMetaData]*) except+ nogil
+        void GetColumnFamilyMetaData(ColumnFamilyHandle*, ColumnFamilyMetaData*) except+ nogil
         ColumnFamilyHandle* DefaultColumnFamily()
         Status TryCatchUpWithPrimary() nogil except+
 
@@ -187,14 +187,14 @@ cdef extern from "rocksdb/db.h" namespace "rocksdb":
     cdef Status DB_Open "rocksdb::DB::Open"(
         const options.Options&,
         const string&,
-        DB**) nogil except+
+        DB**) except+ nogil
 
     cdef Status DB_Open_ColumnFamilies "rocksdb::DB::Open"(
         const options.Options&,
         const string&,
         const vector[ColumnFamilyDescriptor]&,
         vector[ColumnFamilyHandle*]*,
-        DB**) nogil except+
+        DB**) except+ nogil
 
     cdef Status DB_OpenAsSecondary "rocksdb::DB::OpenAsSecondary"(
         const options.Options&,
@@ -214,7 +214,7 @@ cdef extern from "rocksdb/db.h" namespace "rocksdb":
         const options.Options&,
         const string&,
         DB**,
-        cpp_bool) nogil except+
+        cpp_bool) except+ nogil
 
     cdef Status DB_OpenForReadOnly_ColumnFamilies "rocksdb::DB::OpenForReadOnly"(
         const options.Options&,
@@ -222,26 +222,26 @@ cdef extern from "rocksdb/db.h" namespace "rocksdb":
         const vector[ColumnFamilyDescriptor]&,
         vector[ColumnFamilyHandle*]*,
         DB**,
-        cpp_bool) nogil except+
+        cpp_bool) except+ nogil
 
     cdef Status RepairDB(const string& dbname, const options.Options&)
 
     cdef Status ListColumnFamilies "rocksdb::DB::ListColumnFamilies" (
         const options.Options&,
         const string&,
-        vector[string]*) nogil except+
+        vector[string]*) except+ nogil
 
     cdef cppclass ColumnFamilyHandle:
-        const string& GetName() nogil except+
-        int GetID() nogil except+
+        const string& GetName() except+ nogil
+        uint32_t GetID() except+ nogil
 
     cdef cppclass ColumnFamilyDescriptor:
-        ColumnFamilyDescriptor() nogil except+
+        ColumnFamilyDescriptor() except+ nogil
         ColumnFamilyDescriptor(
 	    const string&,
-            const options.ColumnFamilyOptions&) nogil except+
+            const options.ColumnFamilyOptions&) except+ nogil
         string name
         options.ColumnFamilyOptions options
 
 cdef extern from "rocksdb/convenience.h" namespace "rocksdb":
-    void CancelAllBackgroundWork(DB*, cpp_bool) nogil except+
+    void CancelAllBackgroundWork(DB*, cpp_bool) except+ nogil
diff --git a/rocksdb/iterator.pxd b/rocksdb/iterator.pxd
index 748e4db..99a79df 100644
--- a/rocksdb/iterator.pxd
+++ b/rocksdb/iterator.pxd
@@ -4,13 +4,13 @@ from .status cimport Status
 
 cdef extern from "rocksdb/iterator.h" namespace "rocksdb":
     cdef cppclass Iterator:
-        cpp_bool Valid() nogil except+
-        void SeekToFirst() nogil except+
-        void SeekToLast() nogil except+
-        void Seek(const Slice&) nogil except+
-        void Next() nogil except+
-        void Prev() nogil except+
-        void SeekForPrev(const Slice&) nogil except+
-        Slice key() nogil except+
-        Slice value() nogil except+
-        Status status() nogil except+
+        cpp_bool Valid() except+ nogil
+        void SeekToFirst() except+ nogil
+        void SeekToLast() except+ nogil
+        void Seek(const Slice&) except+ nogil
+        void Next() except+ nogil
+        void Prev() except+ nogil
+        void SeekForPrev(const Slice&) except+ nogil
+        Slice key() except+ nogil
+        Slice value() except+ nogil
+        Status status() except+ nogil
diff --git a/rocksdb/logger.pxd b/rocksdb/logger.pxd
index d0b7b72..31c29c9 100644
--- a/rocksdb/logger.pxd
+++ b/rocksdb/logger.pxd
@@ -2,4 +2,4 @@ cdef extern from "rocksdb/env.h" namespace "rocksdb":
     cdef cppclass Logger:
         pass
 
-    void Log(Logger*, const char*, ...) nogil except+
+    void Log(Logger*, const char*, ...) except+ nogil
diff --git a/rocksdb/merge_operator.pxd b/rocksdb/merge_operator.pxd
index 510d5cd..42af21b 100644
--- a/rocksdb/merge_operator.pxd
+++ b/rocksdb/merge_operator.pxd
@@ -35,7 +35,7 @@ ctypedef cpp_bool (*partial_merge_func)(
 
 cdef extern from "cpp/merge_operator_wrapper.hpp" namespace "py_rocks":
     cdef cppclass AssociativeMergeOperatorWrapper:
-        AssociativeMergeOperatorWrapper(string, void*, merge_func) nogil except+
+        AssociativeMergeOperatorWrapper(string, void*, merge_func) except+ nogil
 
     cdef cppclass MergeOperatorWrapper:
         MergeOperatorWrapper(
@@ -43,4 +43,4 @@ cdef extern from "cpp/merge_operator_wrapper.hpp" namespace "py_rocks":
             void*,
             void*,
             full_merge_func,
-            partial_merge_func) nogil except+
+            partial_merge_func) except+ nogil
diff --git a/rocksdb/options.pxd b/rocksdb/options.pxd
index c2f2430..651e51d 100644
--- a/rocksdb/options.pxd
+++ b/rocksdb/options.pxd
@@ -105,7 +105,7 @@ cdef extern from "rocksdb/options.h" namespace "rocksdb":
         cpp_bool allow_concurrent_memtable_write
         cpp_bool enable_write_thread_adaptive_yield
         shared_ptr[Cache] row_cache
-        void IncreaseParallelism(int) nogil except+
+        void IncreaseParallelism(int) except+ nogil
 
     cdef cppclass ColumnFamilyOptions:
         ColumnFamilyOptions()
diff --git a/rocksdb/slice_transform.pxd b/rocksdb/slice_transform.pxd
index dd73502..bfd4c2f 100644
--- a/rocksdb/slice_transform.pxd
+++ b/rocksdb/slice_transform.pxd
@@ -9,10 +9,10 @@ cdef extern from "rocksdb/slice_transform.h" namespace "rocksdb":
         pass
 
     cdef const SliceTransform* ST_NewCappedPrefixTransform "rocksdb::NewCappedPrefixTransform"(
-        size_t) nogil except+
+        size_t) except+ nogil
 
     cdef const SliceTransform* ST_NewFixedPrefixTransform "rocksdb::NewFixedPrefixTransform"(
-        size_t) nogil except+
+        size_t) except+ nogil
 
 ctypedef Slice (*transform_func)(
     void*,
@@ -39,5 +39,5 @@ cdef extern from "cpp/slice_transform_wrapper.hpp" namespace "py_rocks":
                 void*,
                 transform_func,
                 in_domain_func,
-                in_range_func) nogil except+
-        void set_info_log(shared_ptr[Logger]) nogil except+
+                in_range_func) except+ nogil
+        void set_info_log(shared_ptr[Logger]) except+ nogil
diff --git a/rocksdb/statistics.pxd b/rocksdb/statistics.pxd
index 1028c8a..d673bce 100644
--- a/rocksdb/statistics.pxd
+++ b/rocksdb/statistics.pxd
@@ -10,4 +10,4 @@ cdef extern from "rocksdb/statistics.h" namespace "rocksdb":
         kAll
 
     cdef cppclass Statistics:
-        void set_stats_level(StatsLevel) nogil except+
+        void set_stats_level(StatsLevel) except+ nogil
diff --git a/rocksdb/status.pxd b/rocksdb/status.pxd
index f92bbf1..0dbee00 100644
--- a/rocksdb/status.pxd
+++ b/rocksdb/status.pxd
@@ -12,4 +12,4 @@ cdef extern from "rocksdb/status.h" namespace "rocksdb":
         cpp_bool IsIOError() nogil const
         cpp_bool IsMergeInProgress() nogil const
         cpp_bool IsIncomplete() nogil const
-        string ToString() nogil except+
+        string ToString() except+ nogil
diff --git a/rocksdb/std_memory.pxd b/rocksdb/std_memory.pxd
index ea573ee..4d543ad 100644
--- a/rocksdb/std_memory.pxd
+++ b/rocksdb/std_memory.pxd
@@ -1,7 +1,7 @@
 cdef extern from "<memory>" namespace "std":
     cdef cppclass shared_ptr[T]:
-        shared_ptr() nogil except+
-        shared_ptr(T*) nogil except+
-        void reset() nogil except+
-        void reset(T*) nogil except+
-        T* get() nogil except+
+        shared_ptr() except+ nogil
+        shared_ptr(T*) except+ nogil
+        void reset() except+ nogil
+        void reset(T*) except+ nogil
+        T* get() except+ nogil
diff --git a/rocksdb/types.pxd b/rocksdb/types.pxd
index b8c9ca9..7b06008 100644
--- a/rocksdb/types.pxd
+++ b/rocksdb/types.pxd
@@ -22,7 +22,7 @@ cdef extern from "rocksdb/types.h" namespace "rocksdb":
 
         FullKey() except+
         FullKey(const Slice&, const SequenceNumber&, EntryType) except+
-        string DebugString(cpp_bool hex) nogil except+
-        void clear() nogil except+
+        string DebugString(cpp_bool hex) except+ nogil
+        void clear() except+ nogil
 
     cpp_bool ParseFullKey(const Slice&, FullKey*)