diff --git a/libraries/liblmdb/lmdb.h b/libraries/liblmdb/lmdb.h
index 1e934f4..19fb1fe 100644
--- a/libraries/liblmdb/lmdb.h
+++ b/libraries/liblmdb/lmdb.h
@@ -431,7 +431,7 @@ typedef enum MDB_cursor_op {
 #define MDB_INCOMPATIBLE	(-30784)
 	/** Invalid reuse of reader locktable slot */
 #define MDB_BAD_RSLOT		(-30783)
-	/** Transaction cannot recover - it must be aborted */
+	/** Transaction must abort, has a child, or is invalid */
 #define MDB_BAD_TXN			(-30782)
 	/** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
 #define MDB_BAD_VALSIZE		(-30781)
diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 1668cb7..f38d631 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -995,7 +995,8 @@ typedef struct MDB_dbx {
 	 */
 struct MDB_txn {
 	MDB_txn		*mt_parent;		/**< parent of a nested txn */
-	MDB_txn		*mt_child;		/**< nested txn under this txn */
+	/** Nested txn under this txn, set together with flag #MDB_TXN_HAS_CHILD */
+	MDB_txn		*mt_child;
 	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
@@ -1043,8 +1044,9 @@ struct MDB_txn {
 	MDB_cursor	**mt_cursors;
 	/** Array of flags for each DB */
 	unsigned char	*mt_dbflags;
-	/**	Number of DB records in use. This number only ever increments;
-	 *	we don't decrement it when individual DB handles are closed.
+	/**	Number of DB records in use, or 0 when the txn is finished.
+	 *	This number only ever increments until the txn finishes; we
+	 *	don't decrement it when individual DB handles are closed.
 	 */
 	MDB_dbi		mt_numdbs;
 
@@ -1057,9 +1059,13 @@ struct MDB_txn {
 #define MDB_TXN_RDONLY		MDB_RDONLY	/**< read-only transaction */
 	/* internal txn flags */
 #define MDB_TXN_WRITEMAP	MDB_WRITEMAP	/**< copy of #MDB_env flag in writers */
+#define MDB_TXN_FINISHED	0x01		/**< txn is finished or never began */
 #define MDB_TXN_ERROR		0x02		/**< txn is unusable after an error */
 #define MDB_TXN_DIRTY		0x04		/**< must write, even if dirty list is empty */
 #define MDB_TXN_SPILLS		0x08		/**< txn or a parent has spilled pages */
+#define MDB_TXN_HAS_CHILD	0x10		/**< txn has an #MDB_txn.%mt_child */
+	/** most operations on the txn are currently illegal */
+#define MDB_TXN_BLOCKED		(MDB_TXN_FINISHED|MDB_TXN_ERROR|MDB_TXN_HAS_CHILD)
 /** @} */
 	unsigned int	mt_flags;		/**< @ref mdb_txn */
 	/** #dirty_list room: Array size - \#dirty pages visible to this txn.
@@ -1356,7 +1362,7 @@ static char *const mdb_errstr[] = {
 	"MDB_MAP_RESIZED: Database contents grew beyond environment mapsize",
 	"MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed",
 	"MDB_BAD_RSLOT: Invalid reuse of reader locktable slot",
-	"MDB_BAD_TXN: Transaction cannot recover - it must be aborted",
+	"MDB_BAD_TXN: Transaction must abort, has a child, or is invalid",
 	"MDB_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong DUPFIXED size",
 	"MDB_BAD_DBI: The specified DBI handle was closed/changed unexpectedly",
 };
@@ -2725,9 +2731,7 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 	if (parent) {
 		/* Nested transactions: Max 1 child, write txns only, no writemap */
 		flags |= parent->mt_flags;
-		if (parent->mt_child ||
-			(flags & (MDB_RDONLY|MDB_WRITEMAP|MDB_TXN_ERROR)))
-		{
+		if (flags & (MDB_RDONLY|MDB_WRITEMAP|MDB_TXN_BLOCKED)) {
 			return (parent->mt_flags & MDB_TXN_RDONLY) ? EINVAL : MDB_BAD_TXN;
 		}
 		/* Child txns save MDB_pgstate and use own copy of cursors */
@@ -2769,6 +2773,7 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 		txn->mt_u.dirty_list[0].mid = 0;
 		txn->mt_spill_pgs = NULL;
 		txn->mt_next_pgno = parent->mt_next_pgno;
+		parent->mt_flags |= MDB_TXN_HAS_CHILD;
 		parent->mt_child = txn;
 		txn->mt_parent = parent;
 		txn->mt_numdbs = parent->mt_numdbs;
@@ -2885,9 +2890,10 @@ mdb_txn_end(MDB_txn *txn, unsigned mode)
 				txn->mt_u.reader = NULL;
 			} /* else txn owns the slot until it does MDB_END_SLOT */
 		}
-		txn->mt_numdbs = 0;		/* close nothing if called again */
+		txn->mt_numdbs = 0;		/* prevent further DBI activity */
+		txn->mt_flags |= MDB_TXN_FINISHED;
 		txn->mt_dbxs = NULL;	/* mark txn as reset */
-	} else {
+	} else if (!F_ISSET(txn->mt_flags, MDB_TXN_FINISHED)) {
 		pgno_t *pghead = env->me_pghead;
 
 		if (!(mode & MDB_END_UPDATE)) /* !(already closed cursors) */
@@ -2896,6 +2902,9 @@ mdb_txn_end(MDB_txn *txn, unsigned mode)
 			mdb_dlist_free(txn);
 		}
 
+		txn->mt_numdbs = 0;
+		txn->mt_flags = MDB_TXN_FINISHED;
+
 		if (!txn->mt_parent) {
 			mdb_midl_shrink(&txn->mt_free_pgs);
 			env->me_free_pgs = txn->mt_free_pgs;
@@ -2911,6 +2920,7 @@ mdb_txn_end(MDB_txn *txn, unsigned mode)
 				UNLOCK_MUTEX(env->me_wmutex);
 		} else {
 			txn->mt_parent->mt_child = NULL;
+			txn->mt_parent->mt_flags &= ~MDB_TXN_HAS_CHILD;
 			env->me_pgstate = ((MDB_ntxn *)txn)->mnt_pgstate;
 			mdb_midl_free(txn->mt_free_pgs);
 			mdb_midl_free(txn->mt_spill_pgs);
@@ -3318,8 +3328,8 @@ mdb_txn_commit(MDB_txn *txn)
 		goto done;
 	}
 
-	if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
-		DPUTS("error flag is set, can't commit");
+	if (txn->mt_flags & (MDB_TXN_FINISHED|MDB_TXN_ERROR)) {
+		DPUTS("txn has failed/finished, can't commit");
 		if (txn->mt_parent)
 			txn->mt_parent->mt_flags |= MDB_TXN_ERROR;
 		rc = MDB_BAD_TXN;
@@ -4742,6 +4752,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
 				txn->mt_dbflags = (unsigned char *)(txn->mt_dbiseqs + env->me_maxdbs);
 				txn->mt_env = env;
 				txn->mt_dbxs = env->me_dbxs;
+				txn->mt_flags = MDB_TXN_FINISHED;
 				env->me_txn0 = txn;
 			} else {
 				rc = ENOMEM;
@@ -5284,8 +5295,8 @@ mdb_page_search(MDB_cursor *mc, MDB_val *key, int flags)
 	/* Make sure the txn is still viable, then find the root from
 	 * the txn's db table and set it as the root of the cursor's stack.
 	 */
-	if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_ERROR)) {
-		DPUTS("transaction has failed, must abort");
+	if (mc->mc_txn->mt_flags & MDB_TXN_BLOCKED) {
+		DPUTS("transaction may not be used now");
 		return MDB_BAD_TXN;
 	} else {
 		/* Make sure we're using an up-to-date root */
@@ -5472,7 +5483,7 @@ mdb_get(MDB_txn *txn, MDB_dbi dbi,
 	if (!key || !data || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
-	if (txn->mt_flags & MDB_TXN_ERROR)
+	if (txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	mdb_cursor_init(&mc, txn, dbi, &mx);
@@ -5993,7 +6004,7 @@ mdb_cursor_get(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 	if (mc == NULL)
 		return EINVAL;
 
-	if (mc->mc_txn->mt_flags & MDB_TXN_ERROR)
+	if (mc->mc_txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	switch (op) {
@@ -6223,7 +6234,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 	nospill = flags & MDB_NOSPILL;
 	flags &= ~MDB_NOSPILL;
 
-	if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
+	if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED))
 		return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;
 
 	if (key->mv_size-1 >= ENV_MAXKEY(env))
@@ -6716,7 +6727,7 @@ mdb_cursor_del(MDB_cursor *mc, unsigned int flags)
 	MDB_page	*mp;
 	int rc;
 
-	if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
+	if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED))
 		return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;
 
 	if (!(mc->mc_flags & C_INITIALIZED))
@@ -7285,7 +7296,7 @@ mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
 	if (!ret || !TXN_DBI_EXIST(txn, dbi, DB_VALID))
 		return EINVAL;
 
-	if (txn->mt_flags & MDB_TXN_ERROR)
+	if (txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	/* Allow read access to the freelist */
@@ -7320,7 +7331,7 @@ mdb_cursor_renew(MDB_txn *txn, MDB_cursor *mc)
 	if ((mc->mc_flags & C_UNTRACK) || txn->mt_cursors)
 		return EINVAL;
 
-	if (txn->mt_flags & MDB_TXN_ERROR)
+	if (txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	mdb_cursor_init(mc, txn, mc->mc_dbi, mc->mc_xcursor);
@@ -7339,7 +7350,7 @@ mdb_cursor_count(MDB_cursor *mc, size_t *countp)
 	if (mc->mc_xcursor == NULL)
 		return MDB_INCOMPATIBLE;
 
-	if (mc->mc_txn->mt_flags & MDB_TXN_ERROR)
+	if (mc->mc_txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	if (!(mc->mc_flags & C_INITIALIZED))
@@ -8089,7 +8100,7 @@ mdb_del(MDB_txn *txn, MDB_dbi dbi,
 	if (!key || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
-	if (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
+	if (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED))
 		return (txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;
 
 	if (!F_ISSET(txn->mt_dbs[dbi].md_flags, MDB_DUPSORT)) {
@@ -9276,7 +9287,7 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 
 	if (flags & ~VALID_FLAGS)
 		return EINVAL;
-	if (txn->mt_flags & MDB_TXN_ERROR)
+	if (txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	/* main DB? */
@@ -9374,7 +9385,7 @@ mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
 	if (!arg || !TXN_DBI_EXIST(txn, dbi, DB_VALID))
 		return EINVAL;
 
-	if (txn->mt_flags & MDB_TXN_ERROR)
+	if (txn->mt_flags & MDB_TXN_BLOCKED)
 		return MDB_BAD_TXN;
 
 	if (txn->mt_dbflags[dbi] & DB_STALE) {