diff --git a/mdbx.h b/mdbx.h
index 479a3901..acaca64c 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -1944,7 +1944,7 @@ LIBMDBX_API int mdbx_env_set_flags(MDBX_env *env, unsigned flags, int onoff);
  * Returns A non-zero error value on failure and 0 on success, some
  * possible errors are:
  *  - MDBX_EINVAL   = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_env_get_flags(MDBX_env *env, unsigned *flags);
+LIBMDBX_API int mdbx_env_get_flags(const MDBX_env *env, unsigned *flags);
 
 /* Return the path that was used in mdbx_env_open().
  *
@@ -1956,7 +1956,7 @@ LIBMDBX_API int mdbx_env_get_flags(MDBX_env *env, unsigned *flags);
  * Returns A non-zero error value on failure and 0 on success, some
  * possible errors are:
  *  - MDBX_EINVAL   = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_env_get_path(MDBX_env *env, const char **dest);
+LIBMDBX_API int mdbx_env_get_path(const MDBX_env *env, const char **dest);
 
 /* Return the file descriptor for the given environment.
  *
@@ -1969,7 +1969,7 @@ LIBMDBX_API int mdbx_env_get_path(MDBX_env *env, const char **dest);
  * Returns A non-zero error value on failure and 0 on success, some
  * possible errors are:
  *  - MDBX_EINVAL   = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_env_get_fd(MDBX_env *env, mdbx_filehandle_t *fd);
+LIBMDBX_API int mdbx_env_get_fd(const MDBX_env *env, mdbx_filehandle_t *fd);
 
 /* Set all size-related parameters of environment, including page size and the
  * min/max size of the memory map.
@@ -2222,7 +2222,7 @@ LIBMDBX_API int mdbx_env_set_maxreaders(MDBX_env *env, unsigned readers);
  * Returns A non-zero error value on failure and 0 on success, some
  * possible errors are:
  *  - MDBX_EINVAL   = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_env_get_maxreaders(MDBX_env *env, unsigned *readers);
+LIBMDBX_API int mdbx_env_get_maxreaders(const MDBX_env *env, unsigned *readers);
 
 /* Set the maximum number of named databases for the environment.
  *
@@ -2253,9 +2253,9 @@ LIBMDBX_API int mdbx_env_set_maxdbs(MDBX_env *env, MDBX_dbi dbs);
  *
  * Returns The maximum size of a key we can write,
  * or -1 if something is wrong. */
-LIBMDBX_API int mdbx_env_get_maxkeysize_ex(MDBX_env *env, unsigned flags);
-LIBMDBX_API int mdbx_env_get_maxvalsize_ex(MDBX_env *env, unsigned flags);
-__deprecated LIBMDBX_API int mdbx_env_get_maxkeysize(MDBX_env *env);
+LIBMDBX_API int mdbx_env_get_maxkeysize_ex(const MDBX_env *env, unsigned flags);
+LIBMDBX_API int mdbx_env_get_maxvalsize_ex(const MDBX_env *env, unsigned flags);
+__deprecated LIBMDBX_API int mdbx_env_get_maxkeysize(const MDBX_env *env);
 
 /* Set application information associated with the MDBX_env.
  *
@@ -2269,7 +2269,7 @@ LIBMDBX_API int mdbx_env_set_userctx(MDBX_env *env, void *ctx);
  *
  * [in] env An environment handle returned by mdbx_env_create()
  * Returns The pointer set by mdbx_env_set_userctx(). */
-LIBMDBX_API void *mdbx_env_get_userctx(MDBX_env *env);
+LIBMDBX_API void *mdbx_env_get_userctx(const MDBX_env *env);
 
 /* Create a transaction for use with the environment.
  *
@@ -2382,12 +2382,13 @@ typedef struct MDBX_txn_info {
  *                 not needed (see description of MDBX_txn_info above).
  *
  * Returns A non-zero error value on failure and 0 on success. */
-LIBMDBX_API int mdbx_txn_info(MDBX_txn *txn, MDBX_txn_info *info, int scan_rlt);
+LIBMDBX_API int mdbx_txn_info(const MDBX_txn *txn, MDBX_txn_info *info,
+                              int scan_rlt);
 
 /* Returns the transaction's MDBX_env.
  *
  * [in] txn  A transaction handle returned by mdbx_txn_begin() */
-LIBMDBX_API MDBX_env *mdbx_txn_env(MDBX_txn *txn);
+LIBMDBX_API MDBX_env *mdbx_txn_env(const MDBX_txn *txn);
 
 /* Return the transaction's flags.
  *
@@ -2397,7 +2398,7 @@ LIBMDBX_API MDBX_env *mdbx_txn_env(MDBX_txn *txn);
  *
  * Returns A transaction flags, valid if input is an valid transaction,
  * otherwise -1. */
-LIBMDBX_API int mdbx_txn_flags(MDBX_txn *txn);
+LIBMDBX_API int mdbx_txn_flags(const MDBX_txn *txn);
 
 /* Return the transaction's ID.
  *
@@ -2409,7 +2410,7 @@ LIBMDBX_API int mdbx_txn_flags(MDBX_txn *txn);
  *
  * Returns A transaction ID, valid if input is an active transaction,
  * otherwise 0. */
-LIBMDBX_API uint64_t mdbx_txn_id(MDBX_txn *txn);
+LIBMDBX_API uint64_t mdbx_txn_id(const MDBX_txn *txn);
 
 /* Commit all the operations of a transaction into the database.
  *
@@ -2516,7 +2517,7 @@ LIBMDBX_API int mdbx_canary_put(MDBX_txn *txn, const mdbx_canary *canary);
  *              will be copied.
  *
  * Returns A non-zero error value on failure and 0 on success. */
-LIBMDBX_API int mdbx_canary_get(MDBX_txn *txn, mdbx_canary *canary);
+LIBMDBX_API int mdbx_canary_get(const MDBX_txn *txn, mdbx_canary *canary);
 
 /* A callback function used to compare two keys in a database */
 typedef int(MDBX_cmp_func)(const MDBX_val *a, const MDBX_val *b);
@@ -2732,7 +2733,7 @@ LIBMDBX_API int mdbx_drop(MDBX_txn *txn, MDBX_dbi dbi, int del);
  * possible errors are:
  *  - MDBX_NOTFOUND  = the key was not in the database.
  *  - MDBX_EINVAL    = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
+LIBMDBX_API int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                          MDBX_val *data);
 
 /* Get items from a database and optionaly number of data items for a given key.
@@ -2844,7 +2845,7 @@ LIBMDBX_API int mdbx_get_nearest(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
  *  - MDBX_TXN_FULL  = the transaction has too many dirty pages.
  *  - MDBX_EACCES    = an attempt was made to write in a read-only transaction.
  *  - MDBX_EINVAL    = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
+LIBMDBX_API int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                          MDBX_val *data, unsigned flags);
 
 /* Replace items in a database.
@@ -2883,7 +2884,7 @@ LIBMDBX_API int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
  *                     multi-value/duplicates.
  *
  * Returns A non-zero error value on failure and 0 on success. */
-LIBMDBX_API int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
+LIBMDBX_API int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                              MDBX_val *new_data, MDBX_val *old_data,
                              unsigned flags);
 
@@ -2907,8 +2908,8 @@ LIBMDBX_API int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
  * possible errors are:
  *  - MDBX_EACCES   = an attempt was made to write in a read-only transaction.
  *  - MDBX_EINVAL   = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
-                         MDBX_val *data);
+LIBMDBX_API int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
+                         const MDBX_val *data);
 
 /* Create a cursor handle.
  *
@@ -2972,12 +2973,12 @@ LIBMDBX_API int mdbx_cursor_renew(MDBX_txn *txn, MDBX_cursor *cursor);
 /* Return the cursor's transaction handle.
  *
  * [in] cursor A cursor handle returned by mdbx_cursor_open(). */
-LIBMDBX_API MDBX_txn *mdbx_cursor_txn(MDBX_cursor *cursor);
+LIBMDBX_API MDBX_txn *mdbx_cursor_txn(const MDBX_cursor *cursor);
 
 /* Return the cursor's database handle.
  *
  * [in] cursor  A cursor handle returned by mdbx_cursor_open(). */
-LIBMDBX_API MDBX_dbi mdbx_cursor_dbi(MDBX_cursor *cursor);
+LIBMDBX_API MDBX_dbi mdbx_cursor_dbi(const MDBX_cursor *cursor);
 
 /* Retrieve by cursor.
  *
@@ -3004,11 +3005,11 @@ LIBMDBX_API int mdbx_cursor_get(MDBX_cursor *cursor, MDBX_val *key,
  * This function stores key/data pairs into the database. The cursor is
  * positioned at the new item, or on failure usually near it.
  *
- * [in] cursor  A cursor handle returned by mdbx_cursor_open().
- * [in] key     The key operated on.
- * [in] data    The data operated on.
- * [in] flags   Options for this operation. This parameter
- *              must be set to 0 or one of the values described here:
+ * [in] cursor    A cursor handle returned by mdbx_cursor_open().
+ * [in] key       The key operated on.
+ * [in,out] data  The data operated on.
+ * [in] flags     Options for this operation. This parameter
+ *                must be set to 0 or one of the values described here:
  *
  *  - MDBX_CURRENT
  *      Replace the item at the current cursor position. The key parameter
@@ -3065,7 +3066,7 @@ LIBMDBX_API int mdbx_cursor_get(MDBX_cursor *cursor, MDBX_val *key,
  *  - MDBX_TXN_FULL  = the transaction has too many dirty pages.
  *  - MDBX_EACCES    = an attempt was made to write in a read-only transaction.
  *  - MDBX_EINVAL    = an invalid parameter was specified. */
-LIBMDBX_API int mdbx_cursor_put(MDBX_cursor *cursor, MDBX_val *key,
+LIBMDBX_API int mdbx_cursor_put(MDBX_cursor *cursor, const MDBX_val *key,
                                 MDBX_val *data, unsigned flags);
 
 /* Delete current key/data pair.
@@ -3101,7 +3102,7 @@ LIBMDBX_API int mdbx_cursor_del(MDBX_cursor *cursor, unsigned flags);
  * possible errors are:
  *  - MDBX_EINVAL   = cursor is not initialized, or an invalid parameter
  *                    was specified. */
-LIBMDBX_API int mdbx_cursor_count(MDBX_cursor *cursor, size_t *countp);
+LIBMDBX_API int mdbx_cursor_count(const MDBX_cursor *cursor, size_t *countp);
 
 /* Determines whether the cursor is pointed to a key-value pair or not,
  * i.e. was not positioned or points to the end of data.
@@ -3112,7 +3113,7 @@ LIBMDBX_API int mdbx_cursor_count(MDBX_cursor *cursor, size_t *countp);
  *  - MDBX_RESULT_TRUE    = no more data available or cursor not positioned;
  *  - MDBX_RESULT_FALSE   = data available;
  *  - Otherwise the error code. */
-LIBMDBX_API int mdbx_cursor_eof(MDBX_cursor *mc);
+LIBMDBX_API int mdbx_cursor_eof(const MDBX_cursor *mc);
 
 /* Determines whether the cursor is pointed to the first key-value pair or not.
  *
@@ -3122,7 +3123,7 @@ LIBMDBX_API int mdbx_cursor_eof(MDBX_cursor *mc);
  *  - MDBX_RESULT_TRUE    = cursor positioned to the first key-value pair.
  *  - MDBX_RESULT_FALSE   = cursor NOT positioned to the first key-value pair.
  *  - Otherwise the error code. */
-LIBMDBX_API int mdbx_cursor_on_first(MDBX_cursor *mc);
+LIBMDBX_API int mdbx_cursor_on_first(const MDBX_cursor *mc);
 
 /* Determines whether the cursor is pointed to the last key-value pair or not.
  *
@@ -3132,7 +3133,7 @@ LIBMDBX_API int mdbx_cursor_on_first(MDBX_cursor *mc);
  *  - MDBX_RESULT_TRUE    = cursor positioned to the last key-value pair.
  *  - MDBX_RESULT_FALSE   = cursor NOT positioned to the last key-value pair.
  *  - Otherwise the error code. */
-LIBMDBX_API int mdbx_cursor_on_last(MDBX_cursor *mc);
+LIBMDBX_API int mdbx_cursor_on_last(const MDBX_cursor *mc);
 
 /* Estimates the distance between cursors as a number of elements. The results
  * of such estimation can be used to build and/or optimize query execution
@@ -3287,7 +3288,7 @@ LIBMDBX_API int mdbx_dbi_sequence(MDBX_txn *txn, MDBX_dbi dbi, uint64_t *result,
  * [in] b     The second item to compare.
  *
  * Returns < 0 if a < b, 0 if a == b, > 0 if a > b */
-LIBMDBX_API int mdbx_cmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
+LIBMDBX_API int mdbx_cmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
                          const MDBX_val *b);
 
 /* Compare two data items according to a particular database.
@@ -3301,7 +3302,7 @@ LIBMDBX_API int mdbx_cmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
  * [in] b     The second item to compare.
  *
  * Returns < 0 if a < b, 0 if a == b, > 0 if a > b */
-LIBMDBX_API int mdbx_dcmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
+LIBMDBX_API int mdbx_dcmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
                           const MDBX_val *b);
 
 /* A callback function used to enumerate the reader lock table.
@@ -3337,8 +3338,8 @@ typedef int(MDBX_reader_list_func)(void *ctx, int num, int slot, mdbx_pid_t pid,
  *
  * Returns A non-zero error value on failure and 0 on success,
  * or MDBX_RESULT_TRUE (-1) if the reader lock table is empty. */
-LIBMDBX_API int mdbx_reader_list(MDBX_env *env, MDBX_reader_list_func *func,
-                                 void *ctx);
+LIBMDBX_API int mdbx_reader_list(const MDBX_env *env,
+                                 MDBX_reader_list_func *func, void *ctx);
 
 /* Check for stale entries in the reader lock table.
  *
@@ -3360,7 +3361,8 @@ LIBMDBX_API int mdbx_reader_check(MDBX_env *env, int *dead);
  *
  * Returns Number of transactions committed after the given was started for
  * read, or negative value on failure. */
-__deprecated LIBMDBX_API int mdbx_txn_straggler(MDBX_txn *txn, int *percent);
+__deprecated LIBMDBX_API int mdbx_txn_straggler(const MDBX_txn *txn,
+                                                int *percent);
 
 /* A lack-of-space callback function to resolve issues with a laggard readers.
  *
@@ -3433,7 +3435,7 @@ LIBMDBX_API int mdbx_env_set_oomfunc(MDBX_env *env, MDBX_oom_func *oom_func);
  * [in] env   An environment handle returned by mdbx_env_create().
  *
  * Returns A MDBX_oom_func function or NULL if disabled. */
-LIBMDBX_API MDBX_oom_func *mdbx_env_get_oomfunc(MDBX_env *env);
+LIBMDBX_API MDBX_oom_func *mdbx_env_get_oomfunc(const MDBX_env *env);
 
 /**** B-tree Traversal *********************************************************
  * This is internal API for mdbx_chk tool. You should avoid to use it, except
diff --git a/src/core.c b/src/core.c
index 9f064a3a..1c4b815e 100644
--- a/src/core.c
+++ b/src/core.c
@@ -334,11 +334,11 @@ node_largedata_pgno(const MDBX_node *const __restrict node) {
 #define LEAF_NODEMAX(pagesize) (PAGEROOM(pagesize) - sizeof(indx_t))
 #define MAX_GC1OVPAGE(pagesize) (PAGEROOM(pagesize) / sizeof(pgno_t) - 1)
 
-__cold int mdbx_env_get_maxkeysize(MDBX_env *env) {
+__cold int mdbx_env_get_maxkeysize(const MDBX_env *env) {
   return mdbx_env_get_maxkeysize_ex(env, MDBX_DUPSORT);
 }
 
-__cold int mdbx_env_get_maxkeysize_ex(MDBX_env *env, unsigned flags) {
+__cold int mdbx_env_get_maxkeysize_ex(const MDBX_env *env, unsigned flags) {
   if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
     return -1;
 
@@ -370,7 +370,7 @@ __cold intptr_t mdbx_limits_keysize_max(intptr_t pagesize, unsigned flags) {
   return BRANCH_NODEMAX(pagesize) - NODESIZE - sizeof(pgno_t);
 }
 
-__cold int mdbx_env_get_maxvalsize_ex(MDBX_env *env, unsigned flags) {
+__cold int mdbx_env_get_maxvalsize_ex(const MDBX_env *env, unsigned flags) {
   if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
     return -1;
 
@@ -3130,8 +3130,8 @@ static int __must_check_result mdbx_page_check(MDBX_env *env,
 static int __must_check_result mdbx_cursor_check(MDBX_cursor *mc, bool pending);
 static int __must_check_result mdbx_cursor_del0(MDBX_cursor *mc);
 static int __must_check_result mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi,
-                                         MDBX_val *key, MDBX_val *data,
-                                         unsigned flags);
+                                         const MDBX_val *key,
+                                         const MDBX_val *data, unsigned flags);
 static int __must_check_result mdbx_cursor_sibling(MDBX_cursor *mc,
                                                    int move_right);
 static int __must_check_result mdbx_cursor_next(MDBX_cursor *mc, MDBX_val *key,
@@ -3517,13 +3517,13 @@ static __maybe_unused void mdbx_page_list(MDBX_page *mp) {
     *tp = tracked->mc_next;                                                    \
   } while (0)
 
-int mdbx_cmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
+int mdbx_cmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
              const MDBX_val *b) {
   mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
   return txn->mt_dbxs[dbi].md_cmp(a, b);
 }
 
-int mdbx_dcmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
+int mdbx_dcmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
               const MDBX_val *b) {
   mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
   return txn->mt_dbxs[dbi].md_dcmp(a, b);
@@ -4138,7 +4138,8 @@ mark_done:
  * [in] data  For a put operation, the data being stored.
  *
  * Returns 0 on success, non-zero on failure. */
-static int mdbx_page_spill(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data) {
+static int mdbx_page_spill(MDBX_cursor *mc, const MDBX_val *key,
+                           const MDBX_val *data) {
   if (mc->mc_flags & C_SUB)
     return MDBX_SUCCESS;
 
@@ -4433,7 +4434,7 @@ static const char *mdbx_durable_str(const MDBX_meta *const meta) {
 /*----------------------------------------------------------------------------*/
 
 /* Find oldest txnid still referenced. */
-static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
+static txnid_t mdbx_find_oldest(const MDBX_txn *txn) {
   mdbx_tassert(txn, (txn->mt_flags & MDBX_RDONLY) == 0);
   MDBX_env *env = txn->mt_env;
   const txnid_t edge = mdbx_recent_steady_txnid(env);
@@ -6316,7 +6317,7 @@ int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, unsigned flags,
   return rc;
 }
 
-int mdbx_txn_info(MDBX_txn *txn, MDBX_txn_info *info, int scan_rlt) {
+int mdbx_txn_info(const MDBX_txn *txn, MDBX_txn_info *info, int scan_rlt) {
   int rc = check_txn(txn, MDBX_TXN_BLOCKED - MDBX_TXN_HAS_CHILD);
   if (unlikely(rc != MDBX_SUCCESS))
     return rc;
@@ -6430,20 +6431,20 @@ int mdbx_txn_info(MDBX_txn *txn, MDBX_txn_info *info, int scan_rlt) {
   return MDBX_SUCCESS;
 }
 
-MDBX_env *mdbx_txn_env(MDBX_txn *txn) {
+MDBX_env *mdbx_txn_env(const MDBX_txn *txn) {
   if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE ||
                txn->mt_env->me_signature != MDBX_ME_SIGNATURE))
     return NULL;
   return txn->mt_env;
 }
 
-uint64_t mdbx_txn_id(MDBX_txn *txn) {
+uint64_t mdbx_txn_id(const MDBX_txn *txn) {
   if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
     return 0;
   return txn->mt_txnid;
 }
 
-int mdbx_txn_flags(MDBX_txn *txn) {
+int mdbx_txn_flags(const MDBX_txn *txn) {
   if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
     return -1;
   return txn->mt_flags;
@@ -9146,7 +9147,7 @@ int __cold mdbx_env_set_maxreaders(MDBX_env *env, unsigned readers) {
   return MDBX_SUCCESS;
 }
 
-int __cold mdbx_env_get_maxreaders(MDBX_env *env, unsigned *readers) {
+int __cold mdbx_env_get_maxreaders(const MDBX_env *env, unsigned *readers) {
   if (!env || !readers)
     return MDBX_EINVAL;
 
@@ -10839,7 +10840,7 @@ static __always_inline int mdbx_node_read(MDBX_cursor *mc, MDBX_node *node,
   return MDBX_SUCCESS;
 }
 
-int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
+int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key, MDBX_val *data) {
   DKBUF;
   mdbx_debug("===> get db %u key [%s]", dbi, DKEY(key));
 
@@ -10859,7 +10860,7 @@ int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
     return rc;
 
   int exact = 0;
-  return mdbx_cursor_set(&cx.outer, key, data, MDBX_SET, &exact);
+  return mdbx_cursor_set(&cx.outer, (MDBX_val *)key, data, MDBX_SET, &exact);
 }
 
 int mdbx_get_nearest(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
@@ -11681,7 +11682,7 @@ static int mdbx_cursor_touch(MDBX_cursor *mc) {
   return rc;
 }
 
-int mdbx_cursor_put(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
+int mdbx_cursor_put(MDBX_cursor *mc, const MDBX_val *key, MDBX_val *data,
                     unsigned flags) {
   MDBX_env *env;
   MDBX_page *sub_root = NULL;
@@ -11831,7 +11832,7 @@ int mdbx_cursor_put(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
         }
       }
     } else {
-      rc = mdbx_cursor_set(mc, key, &d2, MDBX_SET, &exact);
+      rc = mdbx_cursor_set(mc, (MDBX_val *)key, &d2, MDBX_SET, &exact);
     }
     if ((flags & MDBX_NOOVERWRITE) &&
         (rc == MDBX_SUCCESS || rc == MDBX_EKEYMISMATCH)) {
@@ -13005,7 +13006,7 @@ int mdbx_cursor_renew(MDBX_txn *txn, MDBX_cursor *mc) {
 }
 
 /* Return the count of duplicate data items for the current key */
-int mdbx_cursor_count(MDBX_cursor *mc, size_t *countp) {
+int mdbx_cursor_count(const MDBX_cursor *mc, size_t *countp) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;
 
@@ -13069,7 +13070,7 @@ void mdbx_cursor_close(MDBX_cursor *mc) {
   }
 }
 
-MDBX_txn *mdbx_cursor_txn(MDBX_cursor *mc) {
+MDBX_txn *mdbx_cursor_txn(const MDBX_cursor *mc) {
   if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
     return NULL;
   MDBX_txn *txn = mc->mc_txn;
@@ -13080,7 +13081,7 @@ MDBX_txn *mdbx_cursor_txn(MDBX_cursor *mc) {
   return txn;
 }
 
-MDBX_dbi mdbx_cursor_dbi(MDBX_cursor *mc) {
+MDBX_dbi mdbx_cursor_dbi(const MDBX_cursor *mc) {
   if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
     return UINT_MAX;
   return mc->mc_dbi;
@@ -14306,7 +14307,8 @@ static int mdbx_cursor_del0(MDBX_cursor *mc) {
   return rc;
 }
 
-int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
+int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
+             const MDBX_val *data) {
   int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
   if (unlikely(rc != MDBX_SUCCESS))
     return rc;
@@ -14323,8 +14325,8 @@ int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
   return mdbx_del0(txn, dbi, key, data, 0);
 }
 
-static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
-                     unsigned flags) {
+static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
+                     const MDBX_val *data, unsigned flags) {
   MDBX_cursor_couple cx;
   MDBX_cursor_op op;
   MDBX_val rdata;
@@ -14346,7 +14348,8 @@ static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
     op = MDBX_SET;
     flags |= MDBX_NODUPDATA;
   }
-  rc = mdbx_cursor_set(&cx.outer, key, data, op, &exact);
+  rc =
+      mdbx_cursor_set(&cx.outer, (MDBX_val *)key, (MDBX_val *)data, op, &exact);
   if (likely(rc == MDBX_SUCCESS)) {
     /* let mdbx_page_split know about this cursor if needed:
      * delete will trigger a rebalance; if it needs to move
@@ -14846,7 +14849,7 @@ done:
   return rc;
 }
 
-int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
+int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key, MDBX_val *data,
              unsigned flags) {
   int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
   if (unlikely(rc != MDBX_SUCCESS))
@@ -14874,7 +14877,7 @@ int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
 
   /* LY: support for update (explicit overwrite) */
   if (flags & MDBX_CURRENT) {
-    rc = mdbx_cursor_get(&cx.outer, key, NULL, MDBX_SET);
+    rc = mdbx_cursor_get(&cx.outer, (MDBX_val *)key, NULL, MDBX_SET);
     if (likely(rc == MDBX_SUCCESS) &&
         (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT)) {
       /* LY: allows update (explicit overwrite) only for unique keys */
@@ -15535,7 +15538,7 @@ int __cold mdbx_env_set_flags(MDBX_env *env, unsigned flags, int onoff) {
   return MDBX_SUCCESS;
 }
 
-int __cold mdbx_env_get_flags(MDBX_env *env, unsigned *arg) {
+int __cold mdbx_env_get_flags(const MDBX_env *env, unsigned *arg) {
   if (unlikely(!env || !arg))
     return MDBX_EINVAL;
 
@@ -15557,7 +15560,7 @@ int __cold mdbx_env_set_userctx(MDBX_env *env, void *ctx) {
   return MDBX_SUCCESS;
 }
 
-void *__cold mdbx_env_get_userctx(MDBX_env *env) {
+void *__cold mdbx_env_get_userctx(const MDBX_env *env) {
   return env ? env->me_userctx : NULL;
 }
 
@@ -15577,7 +15580,7 @@ int __cold mdbx_env_set_assert(MDBX_env *env, MDBX_assert_func *func) {
 #endif
 }
 
-int __cold mdbx_env_get_path(MDBX_env *env, const char **arg) {
+int __cold mdbx_env_get_path(const MDBX_env *env, const char **arg) {
   if (unlikely(!env || !arg))
     return MDBX_EINVAL;
 
@@ -15588,7 +15591,7 @@ int __cold mdbx_env_get_path(MDBX_env *env, const char **arg) {
   return MDBX_SUCCESS;
 }
 
-int __cold mdbx_env_get_fd(MDBX_env *env, mdbx_filehandle_t *arg) {
+int __cold mdbx_env_get_fd(const MDBX_env *env, mdbx_filehandle_t *arg) {
   if (unlikely(!env || !arg))
     return MDBX_EINVAL;
 
@@ -16314,7 +16317,7 @@ int mdbx_set_dupsort(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cmp_func *cmp) {
   return MDBX_SUCCESS;
 }
 
-int __cold mdbx_reader_list(MDBX_env *env, MDBX_reader_list_func *func,
+int __cold mdbx_reader_list(const MDBX_env *env, MDBX_reader_list_func *func,
                             void *ctx) {
   if (unlikely(!env || !func))
     return MDBX_EINVAL;
@@ -16705,7 +16708,7 @@ int __cold mdbx_env_set_oomfunc(MDBX_env *env, MDBX_oom_func *oomfunc) {
   return MDBX_SUCCESS;
 }
 
-MDBX_oom_func *__cold mdbx_env_get_oomfunc(MDBX_env *env) {
+MDBX_oom_func *__cold mdbx_env_get_oomfunc(const MDBX_env *env) {
   return likely(env && env->me_signature == MDBX_ME_SIGNATURE)
              ? env->me_oom_func
              : NULL;
@@ -16715,7 +16718,7 @@ MDBX_oom_func *__cold mdbx_env_get_oomfunc(MDBX_env *env) {
 /* LY: avoid tsan-trap by me_txn, mm_last_pg and mt_next_pgno */
 __attribute__((__no_sanitize_thread__, __noinline__))
 #endif
-int mdbx_txn_straggler(MDBX_txn *txn, int *percent)
+int mdbx_txn_straggler(const MDBX_txn *txn, int *percent)
 {
   int rc = check_txn(txn, MDBX_TXN_BLOCKED);
   if (unlikely(rc != MDBX_SUCCESS))
@@ -17026,7 +17029,7 @@ int mdbx_canary_put(MDBX_txn *txn, const mdbx_canary *canary) {
   return MDBX_SUCCESS;
 }
 
-int mdbx_canary_get(MDBX_txn *txn, mdbx_canary *canary) {
+int mdbx_canary_get(const MDBX_txn *txn, mdbx_canary *canary) {
   int rc = check_txn(txn, MDBX_TXN_BLOCKED);
   if (unlikely(rc != MDBX_SUCCESS))
     return rc;
@@ -17038,7 +17041,7 @@ int mdbx_canary_get(MDBX_txn *txn, mdbx_canary *canary) {
   return MDBX_SUCCESS;
 }
 
-int mdbx_cursor_on_first(MDBX_cursor *mc) {
+int mdbx_cursor_on_first(const MDBX_cursor *mc) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;
 
@@ -17056,7 +17059,7 @@ int mdbx_cursor_on_first(MDBX_cursor *mc) {
   return MDBX_RESULT_TRUE;
 }
 
-int mdbx_cursor_on_last(MDBX_cursor *mc) {
+int mdbx_cursor_on_last(const MDBX_cursor *mc) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;
 
@@ -17075,7 +17078,7 @@ int mdbx_cursor_on_last(MDBX_cursor *mc) {
   return MDBX_RESULT_TRUE;
 }
 
-int mdbx_cursor_eof(MDBX_cursor *mc) {
+int mdbx_cursor_eof(const MDBX_cursor *mc) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;
 
@@ -17507,8 +17510,8 @@ int mdbx_estimate_range(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *begin_key,
  *  - внешняя аллокация курсоров, в том числе на стеке (без malloc).
  *  - получения статуса страницы по адресу (знать о P_DIRTY).
  */
-int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *new_data,
-                 MDBX_val *old_data, unsigned flags) {
+int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
+                 MDBX_val *new_data, MDBX_val *old_data, unsigned flags) {
   int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
   if (unlikely(rc != MDBX_SUCCESS))
     return rc;