diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index e91233f..143b5a1 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -704,6 +704,8 @@ typedef struct MDB_dbx {
 	 *	Every operation requires a transaction handle.
 	 */
 struct MDB_txn {
+	MDB_txn		*mt_parent;		/**< parent of a nested txn */
+	MDB_txn		*mt_child;		/**< nested txn under this txn */
 	pgno_t		mt_next_pgno;	/**< next unallocated page */
 	/** The ID of this transaction. IDs are integers incrementing from 1.
 	 *	Only committed write transactions increment the ID. If a transaction
@@ -994,6 +996,21 @@ mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
 		return EINVAL;	/* too bad you can't distinguish this from a valid result */
 }
 
+/** Allocate a single page.
+ * Re-use old malloc'd pages first, otherwise just malloc.
+ */
+static MDB_page *
+mdb_page_malloc(MDB_cursor *mc) {
+	MDB_page *ret;
+	if (mc->mc_txn->mt_env->me_dpages) {
+		ret = mc->mc_txn->mt_env->me_dpages;
+		mc->mc_txn->mt_env->me_dpages = ret->mp_next;
+	} else {
+		ret = malloc(mc->mc_txn->mt_env->me_psize);
+	}
+	return ret;
+}
+
 /** Allocate pages for writing.
  * If there are free pages available from older transactions, they
  * will be re-used first. Otherwise a new page will be allocated.
@@ -1142,12 +1159,40 @@ mdb_page_touch(MDB_cursor *mc)
 		mp->mp_pgno = pgno;
 		mp->mp_flags |= P_DIRTY;
 
+finish:
 		mc->mc_pg[mc->mc_top] = mp;
 		/** If this page has a parent, update the parent to point to
 		 * this new page.
 		 */
 		if (mc->mc_top)
 			SETPGNO(NODEPTR(mc->mc_pg[mc->mc_top-1], mc->mc_ki[mc->mc_top-1]), mp->mp_pgno);
+		else
+			mc->mc_db->md_root = mp->mp_pgno;
+	} else if (mc->mc_txn->mt_parent) {
+		MDB_page *np;
+		ID2 mid;
+		/* If txn has a parent, make sure the page is in our
+		 * dirty list.
+		 */
+		if (mc->mc_txn->mt_u.dirty_list[0].mid) {
+			unsigned x = mdb_mid2l_search(mc->mc_txn->mt_u.dirty_list, mp->mp_pgno);
+			if (x <= mc->mc_txn->mt_u.dirty_list[0].mid &&
+				mc->mc_txn->mt_u.dirty_list[x].mid == mp->mp_pgno) {
+				if (mc->mc_txn->mt_u.dirty_list[x].mptr != mp) {
+					mp = mc->mc_txn->mt_u.dirty_list[x].mptr;
+					mc->mc_pg[mc->mc_top] = mp;
+				}
+				return 0;
+			}
+		}
+		/* No - copy it */
+		np = mdb_page_malloc(mc);
+		memcpy(np, mp, mc->mc_txn->mt_env->me_psize);
+		mid.mid = np->mp_pgno;
+		mid.mptr = np;
+		mdb_mid2l_insert(mc->mc_txn->mt_u.dirty_list, &mid);
+		mp = np;
+		goto finish;
 	}
 	return 0;
 }
@@ -1264,7 +1309,7 @@ mdb_txn_renew(MDB_txn *txn)
 }
 
 int
-mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **ret)
+mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 {
 	MDB_txn *txn;
 	int rc;
@@ -1273,6 +1318,12 @@ mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **ret)
 		DPUTS("environment had fatal error, must shutdown!");
 		return MDB_PANIC;
 	}
+	if (parent) {
+		/* parent already has an active child txn */
+		if (parent->mt_child) {
+			return EINVAL;
+		}
+	}
 	if ((txn = calloc(1, sizeof(MDB_txn) +
 		env->me_maxdbs * (sizeof(MDB_db)+1))) == NULL) {
 		DPRINTF("calloc: %s", strerror(ErrCode()));
@@ -1285,7 +1336,33 @@ mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **ret)
 	txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
 	txn->mt_env = env;
 
-	rc = mdb_txn_renew0(txn);
+	if (parent) {
+		txn->mt_free_pgs = mdb_midl_alloc();
+		if (!txn->mt_free_pgs) {
+			free(txn);
+			return ENOMEM;
+		}
+		txn->mt_u.dirty_list = malloc(sizeof(ID2)*MDB_IDL_UM_SIZE);
+		if (!txn->mt_u.dirty_list) {
+			free(txn->mt_free_pgs);
+			free(txn);
+			return ENOMEM;
+		}
+		txn->mt_txnid = parent->mt_txnid;
+		txn->mt_toggle = parent->mt_toggle;
+		txn->mt_u.dirty_list[0].mid = 0;
+		txn->mt_free_pgs[0] = 0;
+		txn->mt_next_pgno = parent->mt_next_pgno;
+		parent->mt_child = txn;
+		txn->mt_parent = parent;
+		txn->mt_numdbs = parent->mt_numdbs;
+		txn->mt_dbxs = parent->mt_dbxs;
+		memcpy(txn->mt_dbs, parent->mt_dbs, txn->mt_numdbs * sizeof(MDB_db));
+		memcpy(txn->mt_dbflags, parent->mt_dbflags, txn->mt_numdbs);
+		rc = 0;
+	} else {
+		rc = mdb_txn_renew0(txn);
+	}
 	if (rc)
 		free(txn);
 	else {
@@ -1313,9 +1390,6 @@ mdb_txn_reset0(MDB_txn *txn)
 		MDB_page *dp;
 		unsigned int i;
 
-		if (mdb_midl_shrink(&txn->mt_free_pgs))
-			env->me_free_pgs = txn->mt_free_pgs;
-
 		/* return all dirty pages to dpage list */
 		for (i=1; i<=txn->mt_u.dirty_list[0].mid; i++) {
 			dp = txn->mt_u.dirty_list[i].mptr;
@@ -1328,6 +1402,16 @@ mdb_txn_reset0(MDB_txn *txn)
 			}
 		}
 
+		if (txn->mt_parent) {
+			txn->mt_parent->mt_child = NULL;
+			free(txn->mt_free_pgs);
+			free(txn->mt_u.dirty_list);
+			return;
+		} else {
+			if (mdb_midl_shrink(&txn->mt_free_pgs))
+				env->me_free_pgs = txn->mt_free_pgs;
+		}
+
 		while ((mop = txn->mt_env->me_pghead)) {
 			txn->mt_env->me_pghead = mop->mo_next;
 			free(mop);
@@ -1362,6 +1446,9 @@ mdb_txn_abort(MDB_txn *txn)
 		txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
 		(void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root);
 
+	if (txn->mt_child)
+		mdb_txn_abort(txn->mt_child);
+
 	mdb_txn_reset0(txn);
 	free(txn);
 }
@@ -1381,6 +1468,11 @@ mdb_txn_commit(MDB_txn *txn)
 	assert(txn != NULL);
 	assert(txn->mt_env != NULL);
 
+	if (txn->mt_child) {
+		mdb_txn_commit(txn->mt_child);
+		txn->mt_child = NULL;
+	}
+
 	env = txn->mt_env;
 
 	if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
@@ -1405,14 +1497,72 @@ mdb_txn_commit(MDB_txn *txn)
 		return MDB_SUCCESS;
 	}
 
-	if (txn != env->me_txn) {
-		DPUTS("attempt to commit unknown transaction");
+
+	if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
+		DPUTS("error flag is set, can't commit");
+		if (txn->mt_parent)
+			txn->mt_parent->mt_flags |= MDB_TXN_ERROR;
 		mdb_txn_abort(txn);
 		return EINVAL;
 	}
 
-	if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
-		DPUTS("error flag is set, can't commit");
+	if (txn->mt_parent) {
+		MDB_db *ip, *jp;
+		MDB_dbi i;
+		unsigned x, y;
+		ID2L dst, src;
+
+		/* Update parent's DB table */
+		ip = &txn->mt_parent->mt_dbs[2];
+		jp = &txn->mt_dbs[2];
+		for (i = 2; i < txn->mt_numdbs; i++) {
+			if (ip->md_root != jp->md_root)
+				*ip = *jp;
+			ip++; jp++;
+		}
+		txn->mt_parent->mt_numdbs = txn->mt_numdbs;
+
+		/* Append our free list to parent's */
+		mdb_midl_append_list(&txn->mt_parent->mt_free_pgs,
+			txn->mt_free_pgs);
+		mdb_midl_free(txn->mt_free_pgs);
+
+		/* Merge our dirty list with parent's */
+		dst = txn->mt_parent->mt_u.dirty_list;
+		src = txn->mt_u.dirty_list;
+		x = mdb_mid2l_search(dst, src[1].mid);
+		for (y=1; y<=src[0].mid; y++) {
+			MDB_page *mp;
+			while (x <= dst[0].mid && dst[x].mid != src[y].mid) x++;
+			if (x > dst[0].mid)
+				break;
+			mp = dst[x].mptr;
+			dp = src[y].mptr;
+			mp->mp_lower = dp->mp_lower;
+			mp->mp_upper = dp->mp_upper;
+			if (IS_LEAF2(mp)) {
+				memcpy(METADATA(mp), METADATA(dp), NUMKEYS(mp) * mp->mp_pad);
+			} else {
+				memcpy((char *)mp+mp->mp_upper, (char *)dp+dp->mp_upper,
+					txn->mt_env->me_psize - mp->mp_upper);
+			}
+			free(src[y].mptr);
+		}
+		x = dst[0].mid;
+		for (; y<=src[0].mid; y++) {
+			if (++x >= MDB_IDL_UM_MAX)
+				return ENOMEM;
+			dst[x] = src[y];
+		}
+		dst[0].mid = x;
+		free(txn->mt_u.dirty_list);
+		txn->mt_parent->mt_child = NULL;
+		free(txn);
+		return MDB_SUCCESS;
+	}
+
+	if (txn != env->me_txn) {
+		DPUTS("attempt to commit unknown transaction");
 		mdb_txn_abort(txn);
 		return EINVAL;
 	}
@@ -1892,6 +2042,8 @@ mdb_env_set_mapsize(MDB_env *env, size_t size)
 	if (env->me_map)
 		return EINVAL;
 	env->me_mapsize = size;
+	if (env->me_psize)
+		env->me_maxpg = env->me_mapsize / env->me_psize;
 	return MDB_SUCCESS;
 }
 
@@ -2896,11 +3048,8 @@ mdb_page_search(MDB_cursor *mc, MDB_val *key, int modify)
 		mc->mc_dbi, root, mc->mc_pg[0]->mp_flags);
 
 	if (modify) {
-		if (!F_ISSET(mc->mc_pg[0]->mp_flags, P_DIRTY)) {
-			if ((rc = mdb_page_touch(mc)))
-				return rc;
-			mc->mc_db->md_root = mc->mc_pg[0]->mp_pgno;
-		}
+		if ((rc = mdb_page_touch(mc)))
+			return rc;
 	}
 
 	return mdb_page_search_root(mc, key, modify);
@@ -3545,15 +3694,9 @@ mdb_cursor_touch(MDB_cursor *mc)
 		*mc->mc_dbflag = DB_DIRTY;
 	}
 	for (mc->mc_top = 0; mc->mc_top < mc->mc_snum; mc->mc_top++) {
-		if (!F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY)) {
-			rc = mdb_page_touch(mc);
-			if (rc)
-				return rc;
-			if (!mc->mc_top) {
-				mc->mc_db->md_root =
-					mc->mc_pg[mc->mc_top]->mp_pgno;
-			}
-		}
+		rc = mdb_page_touch(mc);
+		if (rc)
+			return rc;
 	}
 	mc->mc_top = mc->mc_snum-1;
 	return MDB_SUCCESS;
@@ -3578,7 +3721,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 		return EACCES;
 
 	DPRINTF("==> put db %u key [%s], size %zu, data size %zu",
-		mc->mc_dbi, DKEY(key), key->mv_size, data->mv_size);
+		mc->mc_dbi, DKEY(key), key ? key->mv_size:0, data->mv_size);
 
 	dkey.mv_size = 0;
 
@@ -4969,13 +5112,9 @@ newsep:
 	/* Move half of the keys to the right sibling. */
 
 	/* grab a page to hold a temporary copy */
-	if (mc->mc_txn->mt_env->me_dpages) {
-		copy = mc->mc_txn->mt_env->me_dpages;
-		mc->mc_txn->mt_env->me_dpages = copy->mp_next;
-	} else {
-		if ((copy = malloc(mc->mc_txn->mt_env->me_psize)) == NULL)
-			return ENOMEM;
-	}
+	copy = mdb_page_malloc(mc);
+	if (copy == NULL)
+		return ENOMEM;
 
 	copy->mp_pgno  = mp->mp_pgno;
 	copy->mp_flags = mp->mp_flags;
@@ -5075,14 +5214,14 @@ mdb_put(MDB_txn *txn, MDB_dbi dbi,
 	return mdb_cursor_put(&mc, key, data, flags);
 }
 
+/** Only a subset of the @ref mdb_env flags can be changed
+ *	at runtime. Changing other flags requires closing the environment
+ *	and re-opening it with the new flags.
+ */
+#define	CHANGEABLE	(MDB_NOSYNC)
 int
 mdb_env_set_flags(MDB_env *env, unsigned int flag, int onoff)
 {
-	/** Only a subset of the @ref mdb_env flags can be changed
-	 *	at runtime. Changing other flags requires closing the environment
-	 *	and re-opening it with the new flags.
-	 */
-#define	CHANGEABLE	(MDB_NOSYNC)
 	if ((flag & CHANGEABLE) != flag)
 		return EINVAL;
 	if (onoff)
@@ -5340,7 +5479,7 @@ int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
 	if (rc)
 		return rc;
 
-	rc = mdb_drop0(mc, 1);
+	rc = mdb_drop0(mc, mc->mc_db->md_flags & MDB_DUPSORT);
 	if (rc)
 		mdb_cursor_close(mc);
 		return rc;
diff --git a/libraries/libmdb/mdb.h b/libraries/libmdb/mdb.h
index 18d7368..1672d81 100644
--- a/libraries/libmdb/mdb.h
+++ b/libraries/libmdb/mdb.h
@@ -99,33 +99,39 @@
 	MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
 /**	@} */
 
-/** Opaque structure for a database environment. A DB environment supports multiple
- * databases, all residing in the same shared-memory map.
+/** @brief Opaque structure for a database environment.
+ *
+ * A DB environment supports multiple databases, all residing in the same
+ * shared-memory map.
  */
 typedef struct MDB_env MDB_env;
 
-/** Opaque structure for a transaction handle. All database operations require
- * a transaction handle. Transactions may be read-only or read-write.
+/** @brief Opaque structure for a transaction handle.
+ *
+ * All database operations require a transaction handle. Transactions may be
+ * read-only or read-write.
  */
 typedef struct MDB_txn MDB_txn;
 
-/** A handle for an individual database in the DB environment. */
+/** @brief A handle for an individual database in the DB environment. */
 typedef unsigned int	MDB_dbi;
 
-/** Opaque structure for navigating through a database */
+/** @brief Opaque structure for navigating through a database */
 typedef struct MDB_cursor MDB_cursor;
 
-/** Generic structure used for passing keys and data in and out of the database. */
+/** @brief Generic structure used for passing keys and data in and out of the database. */
 typedef struct MDB_val {
 	size_t		 mv_size;	/**< size of the data item */
 	void		*mv_data;	/**< address of the data item */
 } MDB_val;
 
-/** A callback function used to compare two keys in a database */
+/** @brief A callback function used to compare two keys in a database */
 typedef int  (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
 
-/** A callback function used to relocate a position-dependent data item
- * in a fixed-address database. The \b newptr gives the item's desired address in
+/** @brief A callback function used to relocate a position-dependent data item
+ * in a fixed-address database.
+ *
+ * The \b newptr gives the item's desired address in
  * the memory map, and \b oldptr gives its previous address. The item's actual
  * data resides at the address in \b item.  This callback is expected to walk
  * through the fields of the record in \b item and modify any
@@ -183,7 +189,8 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 #define MDB_CURRENT	0x40
 /*	@} */
 
-/** Cursor Get operations
+/** @brief Cursor Get operations.
+ *
  *	This is the set of all operations for retrieving data
  *	using a cursor.
  */
@@ -235,7 +242,7 @@ typedef enum MDB_cursor_op {
 #define MDB_VERSION_MISMATCH	(-30794)
 /** @} */
 
-/** Statistics for a database in the environment */
+/** @brief Statistics for a database in the environment */
 typedef struct MDB_stat {
 	unsigned int	ms_psize;			/**< Size of a database page.
 											This is currently the same for all databases. */
@@ -246,7 +253,8 @@ typedef struct MDB_stat {
 	size_t		ms_entries;			/**< Number of data items */
 } MDB_stat;
 
-	/** Return the mdb library version information.
+	/** @brief Return the mdb library version information.
+	 *
 	 * @param[out] major if non-NULL, the library major version number is copied here
 	 * @param[out] minor if non-NULL, the library minor version number is copied here
 	 * @param[out] patch if non-NULL, the library patch version number is copied here
@@ -254,7 +262,8 @@ typedef struct MDB_stat {
 	 */
 char *mdb_version(int *major, int *minor, int *patch);
 
-	/** Return a string describing a given error code.
+	/** @brief Return a string describing a given error code.
+	 *
 	 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
 	 * function. If the error code is greater than or equal to 0, then the string
 	 * returned by the system function strerror(3) is returned. If the error code
@@ -265,7 +274,8 @@ char *mdb_version(int *major, int *minor, int *patch);
 	 */
 char *mdb_strerror(int err);
 
-	/** Create an MDB environment handle.
+	/** @brief Create an MDB environment handle.
+	 *
 	 * This function allocates memory for a #MDB_env structure. To release
 	 * the allocated memory and discard the handle, call #mdb_env_close().
 	 * Before the handle may be used, it must be opened using #mdb_env_open().
@@ -277,7 +287,8 @@ char *mdb_strerror(int err);
 	 */
 int  mdb_env_create(MDB_env **env);
 
-	/** Open an environment handle.
+	/** @brief Open an environment handle.
+	 *
 	 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[in] path The directory in which the database files reside. This
@@ -321,14 +332,16 @@ int  mdb_env_create(MDB_env **env);
 	 */
 int  mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
 
-	/** Return statistics about the MDB environment.
+	/** @brief Return statistics about the MDB environment.
+	 *
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[out] stat The address of an #MDB_stat structure
 	 * 	where the statistics will be copied
 	 */
 int  mdb_env_stat(MDB_env *env, MDB_stat *stat);
 
-	/** Flush the data buffers to disk.
+	/** @brief Flush the data buffers to disk.
+	 *
 	 * Data is always written to disk when #mdb_txn_commit() is called,
 	 * but the operating system may keep it buffered. MDB always flushes
 	 * the OS buffers upon commit as well, unless the environment was
@@ -346,7 +359,8 @@ int  mdb_env_stat(MDB_env *env, MDB_stat *stat);
 	 */
 int  mdb_env_sync(MDB_env *env, int force);
 
-	/** Close the environment and release the memory map.
+	/** @brief Close the environment and release the memory map.
+	 *
 	 * Only a single thread may call this function. All transactions, databases,
 	 * and cursors must already be closed before calling this function. Attempts to
 	 * use any such handles after calling this function will cause a SIGSEGV.
@@ -355,7 +369,8 @@ int  mdb_env_sync(MDB_env *env, int force);
 	 */
 void mdb_env_close(MDB_env *env);
 
-	/** Set environment flags.
+	/** @brief Set environment flags.
+	 *
 	 * This may be used to set some flags that weren't already set during
 	 * #mdb_env_open(), or to unset these flags. Currently only the
 	 * #MDB_NOSYNC flag setting may be changed with this function.
@@ -370,7 +385,8 @@ void mdb_env_close(MDB_env *env);
 	 */
 int  mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
 
-	/** Get environment flags.
+	/** @brief Get environment flags.
+	 *
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[out] flags The address of an integer to store the flags
 	 * @return A non-zero error value on failure and 0 on success. Some possible
@@ -381,7 +397,8 @@ int  mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
 	 */
 int  mdb_env_get_flags(MDB_env *env, unsigned int *flags);
 
-	/** Return the path that was used in #mdb_env_open().
+	/** @brief Return the path that was used in #mdb_env_open().
+	 *
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[out] path Address of a string pointer to contain the path. This
 	 * is the actual string in the environment, not a copy. It should not be
@@ -394,7 +411,8 @@ int  mdb_env_get_flags(MDB_env *env, unsigned int *flags);
 	 */
 int  mdb_env_get_path(MDB_env *env, const char **path);
 
-	/** Set the size of the memory map to use for this environment.
+	/** @brief Set the size of the memory map to use for this environment.
+	 *
 	 * The size should be a multiple of the OS page size. The default is
 	 * 10485760 bytes. The size of the memory map is also the maximum size
 	 * of the database. The value should be chosen as large as possible,
@@ -410,7 +428,8 @@ int  mdb_env_get_path(MDB_env *env, const char **path);
 	 */
 int  mdb_env_set_mapsize(MDB_env *env, size_t size);
 
-	/** Set the maximum number of threads for the environment.
+	/** @brief Set the maximum number of threads for the environment.
+	 *
 	 * This defines the number of slots in the lock table that is used to track readers in the
 	 * the environment. The default is 126.
 	 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
@@ -424,7 +443,8 @@ int  mdb_env_set_mapsize(MDB_env *env, size_t size);
 	 */
 int  mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
 
-	/** Get the maximum number of threads for the environment.
+	/** @brief Get the maximum number of threads for the environment.
+	 *
 	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[out] readers Address of an integer to store the number of readers
 	 * @return A non-zero error value on failure and 0 on success. Some possible
@@ -435,7 +455,8 @@ int  mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
 	 */
 int  mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
 
-	/** Set the maximum number of databases for the environment.
+	/** @brief Set the maximum number of databases for the environment.
+	 *
 	 * This function is only needed if multiple databases will be used in the
 	 * environment. Simpler applications that only use a single database can ignore
 	 * this option.
@@ -450,13 +471,19 @@ int  mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
 	 */
 int  mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
 
-	/** Create a transaction for use with the environment.
+	/** @brief Create a transaction for use with the environment.
+	 *
 	 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
 	 * @note Transactions may not span threads, a transaction must only be used by a
 	 * single thread.
 	 * @note Cursors may not span transactions; each cursor must be opened and closed
 	 * within a single transaction.
 	 * @param[in] env An environment handle returned by #mdb_env_create()
+	 * @param[in] parent If this parameter is non-NULL, the new transaction
+	 * will be a nested transaction, with the transaction indicated by \b parent
+	 * as its parent. Transactions may be nested to any level. A parent
+	 * transaction may not issue any other operations besides mdb_txn_begin,
+	 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
 	 * @param[in] flags Special options for this transaction. This parameter
 	 * must be set to 0 or by bitwise OR'ing together one or more of the
 	 * values described here.
@@ -474,9 +501,10 @@ int  mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
 	 *		the reader lock table is full. See #mdb_env_set_maxreaders().
 	 * </ul>
 	 */
-int  mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **txn);
+int  mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
 
-	/** Commit all the operations of a transaction into the database.
+	/** @brief Commit all the operations of a transaction into the database.
+	 *
 	 * All cursors opened within the transaction must be closed before the transaction
 	 * is committed.
 	 * The transaction handle will be freed and must not be used again after this call.
@@ -491,7 +519,8 @@ int  mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **txn);
 	 */
 int  mdb_txn_commit(MDB_txn *txn);
 
-	/** Abandon all the operations of the transaction instead of saving them.
+	/** @brief Abandon all the operations of the transaction instead of saving them.
+	 *
 	 * All cursors opened within the transaction must be closed before the transaction
 	 * is aborted.
 	 * The transaction handle will be freed and must not be used again after this call.
@@ -499,7 +528,8 @@ int  mdb_txn_commit(MDB_txn *txn);
 	 */
 void mdb_txn_abort(MDB_txn *txn);
 
-	/** Reset a read-only transaction.
+	/** @brief Reset a read-only transaction.
+	 *
 	 * This releases the current reader lock but doesn't free the
 	 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
 	 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
@@ -515,7 +545,8 @@ void mdb_txn_abort(MDB_txn *txn);
 	 */
 void mdb_txn_reset(MDB_txn *txn);
 
-	/** Renew a read-only transaction.
+	/** @brief Renew a read-only transaction.
+	 *
 	 * This acquires a new reader lock for a transaction handle that had been
 	 * released by #mdb_txn_reset(). It must be called before a reset transaction
 	 * may be used again.
@@ -530,7 +561,8 @@ void mdb_txn_reset(MDB_txn *txn);
 	 */
 int  mdb_txn_renew(MDB_txn *txn);
 
-	/** Open a database in the environment.
+	/** @brief Open a database in the environment.
+	 *
 	 * The database handle may be discarded by calling #mdb_close(). Only
 	 * one thread should call this function; it is not mutex-protected in
 	 * a read-only transaction.
@@ -580,7 +612,8 @@ int  mdb_txn_renew(MDB_txn *txn);
 	 */
 int  mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
 
-	/** Retrieve statistics for a database.
+	/** @brief Retrieve statistics for a database.
+	 *
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 	 * @param[in] dbi A database handle returned by #mdb_open()
 	 * @param[out] stat The address of an #MDB_stat structure
@@ -593,7 +626,8 @@ int  mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
 	 */
 int  mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
 
-	/** Close a database handle.
+	/** @brief Close a database handle.
+	 *
 	 * This call is not mutex protected. Handles should only be closed by
 	 * a single thread, and only if no other threads are going to reference
 	 * the database handle any further.
@@ -602,7 +636,8 @@ int  mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
 	 */
 void mdb_close(MDB_env *env, MDB_dbi dbi);
 
-	/** Delete a database and/or free all its pages.
+	/** @brief Delete a database and/or free all its pages.
+	 *
 	 * If the \b del parameter is non-zero the DB handle will be closed
 	 * and the DB will be deleted.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
@@ -613,7 +648,8 @@ void mdb_close(MDB_env *env, MDB_dbi dbi);
 	 */
 int  mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
 
-	/** Set a custom key comparison function for a database.
+	/** @brief Set a custom key comparison function for a database.
+	 *
 	 * The comparison function is called whenever it is necessary to compare a
 	 * key specified by the application with a key currently stored in the database.
 	 * If no comparison function is specified, and no speAGAINcial key flags were specified
@@ -633,7 +669,8 @@ int  mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
 	 */
 int  mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
 
-	/** Set a custom data comparison function for a #MDB_DUPSORT database.
+	/** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
+	 *
 	 * This comparison function is called whenever it is necessary to compare a data
 	 * item specified by the application with a data item currently stored in the database.
 	 * This function only takes effect if the database was opened with the #MDB_DUPSORT
@@ -655,7 +692,8 @@ int  mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
 	 */
 int  mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
 
-	/** Set a relocation function for a #MDB_FIXEDMAP database.
+	/** @brief Set a relocation function for a #MDB_FIXEDMAP database.
+	 *
 	 * @todo The relocation function is called whenever it is necessary to move the data
 	 * of an item to a different position in the database (e.g. through tree
 	 * balancing operations, shifts as a result of adds or deletes, etc.). It is
@@ -674,7 +712,8 @@ int  mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
 	 */
 int  mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
 
-	/** Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
+	/** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
+	 *
 	 * See #mdb_set_relfunc and #MDB_rel_func for more details.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 	 * @param[in] dbi A database handle returned by #mdb_open()
@@ -689,7 +728,8 @@ int  mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
 	 */
 int  mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
 
-	/** Get items from a database.
+	/** @brief Get items from a database.
+	 *
 	 * This function retrieves key/data pairs from the database. The address
 	 * and length of the data associated with the specified \b key are returned
 	 * in the structure to which \b data refers.
@@ -714,7 +754,8 @@ int  mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
 	 */
 int  mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
 
-	/** Store items into a database.
+	/** @brief Store items into a database.
+	 *
 	 * This function stores key/data pairs in the database. The default behavior
 	 * is to enter the new key/data pair, replacing any previously existing key
 	 * if duplicates are disallowed, or adding a duplicate data item if
@@ -749,7 +790,8 @@ int  mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
 int  mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
 			    unsigned int flags);
 
-	/** Delete items from a database.
+	/** @brief Delete items from a database.
+	 *
 	 * This function removes key/data pairs from the database.
 	 * If the database does not support sorted duplicate data items
 	 * (#MDB_DUPSORT) the data parameter is ignored.
@@ -772,7 +814,8 @@ int  mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
 	 */
 int  mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
 
-	/** Create a cursor handle.
+	/** @brief Create a cursor handle.
+	 *
 	 * Cursors are associated with a specific transaction and database and
 	 * may not span threads.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
@@ -786,13 +829,15 @@ int  mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
 	 */
 int  mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
 
-	/** Close a cursor handle.
+	/** @brief Close a cursor handle.
+	 *
 	 * The cursor handle will be freed and must not be used again after this call.
 	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
 	 */
 void mdb_cursor_close(MDB_cursor *cursor);
 
-	/** Retrieve by cursor.
+	/** @brief Retrieve by cursor.
+	 *
 	 * This function retrieves key/data pairs from the database. The address and length
 	 * of the key are returned in the object to which \b key refers (except for the
 	 * case of the #MDB_SET option, in which the \b key object is unchanged), and
@@ -815,7 +860,8 @@ void mdb_cursor_close(MDB_cursor *cursor);
 int  mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 			    MDB_cursor_op op);
 
-	/** Store by cursor.
+	/** @brief Store by cursor.
+	 *
 	 * This function stores key/data pairs into the database.
 	 * If the function fails for any reason, the state of the cursor will be
 	 * unchanged. If the function succeeds and an item is inserted into the
@@ -849,7 +895,8 @@ int  mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 int  mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 				unsigned int flags);
 
-	/**  Delete current key/data pair
+	/** @brief Delete current key/data pair
+	 *
 	 * This function deletes the key/data pair to which the cursor refers.
 	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
 	 * @param[in] flags Options for this operation. This parameter
@@ -867,7 +914,8 @@ int  mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 	 */
 int  mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
 
-	/** Return count of duplicates for current key.
+	/** @brief Return count of duplicates for current key.
+	 *
 	 * This call is only valid on databases that support sorted duplicate
 	 * data items #MDB_DUPSORT.
 	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
@@ -880,7 +928,8 @@ int  mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
 	 */
 int  mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
 
-	/** Compare two data items according to a particular database.
+	/** @brief Compare two data items according to a particular database.
+	 *
 	 * This returns a comparison as if the two data items were keys in the
 	 * specified database.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
@@ -891,7 +940,8 @@ int  mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
 	 */
 int  mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
 
-	/** Compare two data items according to a particular database.
+	/** @brief Compare two data items according to a particular database.
+	 *
 	 * This returns a comparison as if the two items were data items of
 	 * a sorted duplicates #MDB_DUPSORT database.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
diff --git a/libraries/libmdb/mdb_stat.c b/libraries/libmdb/mdb_stat.c
index 931ec61..a5f484d 100644
--- a/libraries/libmdb/mdb_stat.c
+++ b/libraries/libmdb/mdb_stat.c
@@ -38,7 +38,7 @@ int main(int argc,char * argv[])
 		printf("mdb_env_open failed, error %d\n", rc);
 		exit(1);
 	}
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	if (rc) {
 		printf("mdb_txn_begin failed, error %d\n", rc);
 		exit(1);
diff --git a/libraries/libmdb/midl.c b/libraries/libmdb/midl.c
index 30f7410..500811f 100644
--- a/libraries/libmdb/midl.c
+++ b/libraries/libmdb/midl.c
@@ -160,6 +160,25 @@ int mdb_midl_append( IDL *idp, ID id )
 	return 0;
 }
 
+int mdb_midl_append_list( IDL *idp, IDL app )
+{
+	IDL ids = *idp;
+	/* Too big? */
+	if (ids[0] + app[0] >= ids[-1]) {
+		IDL idn = ids-1;
+		/* grow it */
+		idn = realloc(idn, (*idn + app[-1]) * sizeof(ID));
+		if (!idn)
+			return -1;
+		*idn++ += app[-1];
+		ids = idn;
+		*idp = ids;
+	}
+	memcpy(&ids[ids[0]+1], &app[1], app[0] * sizeof(ID));
+	ids[0] += app[0];
+	return 0;
+}
+
 /* Quicksort + Insertion sort for small arrays */
 
 #define SMALL	8
diff --git a/libraries/libmdb/midl.h b/libraries/libmdb/midl.h
index f3fb3a0..4c0e615 100644
--- a/libraries/libmdb/midl.h
+++ b/libraries/libmdb/midl.h
@@ -136,6 +136,13 @@ int mdb_midl_shrink(IDL *idp);
 	 */
 int mdb_midl_append( IDL *idp, ID id );
 
+	/** Append an IDL onto an IDL.
+	 * @param[in,out] idp	Address of the IDL to append to.
+	 * @param[in] app	The IDL to append.
+	 * @return	0 on success, -1 if the IDL is too large.
+	 */
+int mdb_midl_append_list( IDL *idp, IDL app );
+
 	/** Sort an IDL.
 	 * @param[in,out] ids	The IDL to sort.
 	 */
diff --git a/libraries/libmdb/mtest.c b/libraries/libmdb/mtest.c
index 89f0ac4..bb5ec81 100644
--- a/libraries/libmdb/mtest.c
+++ b/libraries/libmdb/mtest.c
@@ -42,7 +42,7 @@ int main(int argc,char * argv[])
 		rc = mdb_env_create(&env);
 		rc = mdb_env_set_mapsize(env, 10485760);
 		rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP /*|MDB_NOSYNC*/, 0664);
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		rc = mdb_open(txn, NULL, 0, &dbi);
    
 		key.mv_size = sizeof(int);
@@ -60,7 +60,7 @@ int main(int argc,char * argv[])
 		rc = mdb_txn_commit(txn);
 		rc = mdb_env_stat(env, &mst);
 
-		rc = mdb_txn_begin(env, 1, &txn);
+		rc = mdb_txn_begin(env, NULL, 1, &txn);
 		rc = mdb_cursor_open(txn, dbi, &cursor);
 		while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
 			printf("key: %p %.*s, data: %p %.*s\n",
@@ -75,7 +75,7 @@ int main(int argc,char * argv[])
 	    for (i= count - 1; i > -1; i-= (random()%5)) {	
 			j++;
 			txn=NULL;
-			rc = mdb_txn_begin(env, 0, &txn);
+			rc = mdb_txn_begin(env, NULL, 0, &txn);
 			sprintf(sval, "%03x ", values[i]);
 			rc = mdb_del(txn, dbi, &key, NULL);
 			if (rc) {
@@ -89,7 +89,7 @@ int main(int argc,char * argv[])
 		printf("Deleted %d values\n", j);
 
 		rc = mdb_env_stat(env, &mst);
-		rc = mdb_txn_begin(env, 1, &txn);
+		rc = mdb_txn_begin(env, NULL, 1, &txn);
 		rc = mdb_cursor_open(txn, dbi, &cursor);
 		printf("Cursor next\n");
 		while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
@@ -108,7 +108,7 @@ int main(int argc,char * argv[])
 		 * this stuff all breaks
 		 */
 		printf("Deleting with cursor\n");
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		rc = mdb_cursor_open(db, txn, &cur2);
 		for (i=0; i<50; i++) {
 			rc = mdb_cursor_get(cur2, &key, &data, MDB_NEXT);
diff --git a/libraries/libmdb/mtest2.c b/libraries/libmdb/mtest2.c
index 17c1ecf..a0e9914 100644
--- a/libraries/libmdb/mtest2.c
+++ b/libraries/libmdb/mtest2.c
@@ -46,7 +46,7 @@ int main(int argc,char * argv[])
 	rc = mdb_env_set_mapsize(env, 10485760);
 	rc = mdb_env_set_maxdbs(env, 4);
 	rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP|MDB_NOSYNC, 0664);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_open(txn, "id1", MDB_CREATE, &dbi);
    
 	key.mv_size = sizeof(int);
@@ -64,7 +64,7 @@ int main(int argc,char * argv[])
 	rc = mdb_txn_commit(txn);
 	rc = mdb_env_stat(env, &mst);
 
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
 		printf("key: %p %.*s, data: %p %.*s\n",
@@ -79,7 +79,7 @@ int main(int argc,char * argv[])
 	for (i= count - 1; i > -1; i-= (random()%5)) {	
 		j++;
 		txn=NULL;
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		sprintf(sval, "%03x ", values[i]);
 		rc = mdb_del(txn, dbi, &key, NULL);
 		if (rc) {
@@ -93,7 +93,7 @@ int main(int argc,char * argv[])
 	printf("Deleted %d values\n", j);
 
 	rc = mdb_env_stat(env, &mst);
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	printf("Cursor next\n");
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
diff --git a/libraries/libmdb/mtest3.c b/libraries/libmdb/mtest3.c
index 43e3481..eb9723b 100644
--- a/libraries/libmdb/mtest3.c
+++ b/libraries/libmdb/mtest3.c
@@ -49,7 +49,7 @@ int main(int argc,char * argv[])
 	rc = mdb_env_set_mapsize(env, 10485760);
 	rc = mdb_env_set_maxdbs(env, 4);
 	rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP|MDB_NOSYNC, 0664);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_open(txn, "id2", MDB_CREATE|MDB_DUPSORT, &dbi);
 
 	key.mv_size = sizeof(int);
@@ -69,7 +69,7 @@ int main(int argc,char * argv[])
 	rc = mdb_txn_commit(txn);
 	rc = mdb_env_stat(env, &mst);
 
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
 		printf("key: %p %.*s, data: %p %.*s\n",
@@ -84,7 +84,7 @@ int main(int argc,char * argv[])
 	for (i= count - 1; i > -1; i-= (random()%5)) {
 		j++;
 		txn=NULL;
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		sprintf(kval, "%03x", values[i & ~0x0f]);
 		sprintf(sval, "%03x %d foo bar", values[i], values[i]);
 		key.mv_size = sizeof(int);
@@ -103,7 +103,7 @@ int main(int argc,char * argv[])
 	printf("Deleted %d values\n", j);
 
 	rc = mdb_env_stat(env, &mst);
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	printf("Cursor next\n");
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
diff --git a/libraries/libmdb/mtest4.c b/libraries/libmdb/mtest4.c
index 821055a..b2f5d93 100644
--- a/libraries/libmdb/mtest4.c
+++ b/libraries/libmdb/mtest4.c
@@ -47,7 +47,7 @@ int main(int argc,char * argv[])
 	rc = mdb_env_set_mapsize(env, 10485760);
 	rc = mdb_env_set_maxdbs(env, 4);
 	rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP|MDB_NOSYNC, 0664);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_open(txn, "id2", MDB_CREATE|MDB_DUPSORT|MDB_DUPFIXED, &dbi);
 
 	key.mv_size = sizeof(int);
@@ -68,7 +68,7 @@ int main(int argc,char * argv[])
 
 	/* there should be one full page of dups now.
 	 */
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
 		printf("key: %p %.*s, data: %p %.*s\n",
@@ -90,22 +90,22 @@ int main(int argc,char * argv[])
 	data.mv_data = sval;
 
 	sprintf(sval, "%07x", values[3]+1);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_put(txn, dbi, &key, &data, MDB_NODUPDATA);
 	mdb_txn_abort(txn);
 
 	sprintf(sval, "%07x", values[255]+1);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_put(txn, dbi, &key, &data, MDB_NODUPDATA);
 	mdb_txn_abort(txn);
 
 	sprintf(sval, "%07x", values[500]+1);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_put(txn, dbi, &key, &data, MDB_NODUPDATA);
 	rc = mdb_txn_commit(txn);
 
 	/* Try MDB_NEXT_MULTIPLE */
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT_MULTIPLE)) == 0) {
 		printf("key: %.*s, data: %.*s\n",
@@ -119,7 +119,7 @@ int main(int argc,char * argv[])
 	for (i= count - 1; i > -1; i-= (random()%3)) {
 		j++;
 		txn=NULL;
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		sprintf(sval, "%07x", values[i]);
 		key.mv_size = sizeof(int);
 		key.mv_data = kval;
@@ -137,7 +137,7 @@ int main(int argc,char * argv[])
 	printf("Deleted %d values\n", j);
 
 	rc = mdb_env_stat(env, &mst);
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	printf("Cursor next\n");
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
diff --git a/libraries/libmdb/mtest5.c b/libraries/libmdb/mtest5.c
index 5fb6bb0..c63402e 100644
--- a/libraries/libmdb/mtest5.c
+++ b/libraries/libmdb/mtest5.c
@@ -49,7 +49,7 @@ int main(int argc,char * argv[])
 	rc = mdb_env_set_mapsize(env, 10485760);
 	rc = mdb_env_set_maxdbs(env, 4);
 	rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP|MDB_NOSYNC, 0664);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_open(txn, "id2", MDB_CREATE|MDB_DUPSORT, &dbi);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 
@@ -71,7 +71,7 @@ int main(int argc,char * argv[])
 	rc = mdb_txn_commit(txn);
 	rc = mdb_env_stat(env, &mst);
 
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
 		printf("key: %p %.*s, data: %p %.*s\n",
@@ -86,7 +86,7 @@ int main(int argc,char * argv[])
 	for (i= count - 1; i > -1; i-= (random()%5)) {
 		j++;
 		txn=NULL;
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		sprintf(kval, "%03x", values[i & ~0x0f]);
 		sprintf(sval, "%03x %d foo bar", values[i], values[i]);
 		key.mv_size = sizeof(int);
@@ -105,7 +105,7 @@ int main(int argc,char * argv[])
 	printf("Deleted %d values\n", j);
 
 	rc = mdb_env_stat(env, &mst);
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	printf("Cursor next\n");
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {
diff --git a/libraries/libmdb/mtest6.c b/libraries/libmdb/mtest6.c
index 36ad267..a5bf3a2 100644
--- a/libraries/libmdb/mtest6.c
+++ b/libraries/libmdb/mtest6.c
@@ -42,7 +42,7 @@ int main(int argc,char * argv[])
 	rc = mdb_env_set_mapsize(env, 10485760);
 	rc = mdb_env_set_maxdbs(env, 4);
 	rc = mdb_env_open(env, "./testdb", MDB_FIXEDMAP|MDB_NOSYNC, 0664);
-	rc = mdb_txn_begin(env, 0, &txn);
+	rc = mdb_txn_begin(env, NULL, 0, &txn);
 	rc = mdb_open(txn, "id2", MDB_CREATE|MDB_INTEGERKEY, &dbi);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	rc = mdb_stat(txn, dbi, &mst);
@@ -87,7 +87,7 @@ int main(int argc,char * argv[])
 	for (i= count - 1; i > -1; i-= (random()%5)) {
 		j++;
 		txn=NULL;
-		rc = mdb_txn_begin(env, 0, &txn);
+		rc = mdb_txn_begin(env, NULL, 0, &txn);
 		sprintf(kval, "%03x", values[i & ~0x0f]);
 		sprintf(sval, "%03x %d foo bar", values[i], values[i]);
 		key.mv_size = sizeof(int);
@@ -106,7 +106,7 @@ int main(int argc,char * argv[])
 	printf("Deleted %d values\n", j);
 
 	rc = mdb_env_stat(env, &mst);
-	rc = mdb_txn_begin(env, 1, &txn);
+	rc = mdb_txn_begin(env, NULL, 1, &txn);
 	rc = mdb_cursor_open(txn, dbi, &cursor);
 	printf("Cursor next\n");
 	while ((rc = mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0) {