diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 8a877c744f..a6df703c37 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -691,9 +691,6 @@ typedef struct MDB_meta {
 	/** Auxiliary DB info.
 	 *	The information here is mostly static/read-only. There is
 	 *	only a single copy of this record in the environment.
-	 *	The \b md_dirty flag is not read-only, but only a write
-	 *	transaction can ever update it, and only write transactions
-	 *	need to worry about it.
 	 */
 typedef struct MDB_dbx {
 	MDB_val		md_name;		/**< name of the database */
@@ -701,8 +698,6 @@ typedef struct MDB_dbx {
 	MDB_cmp_func	*md_dcmp;	/**< function for comparing data items */
 	MDB_rel_func	*md_rel;	/**< user relocate function */
 	void		*md_relctx;		/**< user-provided context for md_rel */
-	MDB_dbi	md_parent;			/**< parent DB of a sub-DB */
-	unsigned int	md_dirty;	/**< TRUE if DB was written in this txn */
 } MDB_dbx;
 
 	/** A database transaction.
@@ -717,9 +712,8 @@ struct MDB_txn {
 	txnid_t		mt_txnid;
 	MDB_env		*mt_env;		/**< the DB environment */
 	/** The list of pages that became unused during this transaction.
-	 *	This is an #IDL.
 	 */
-	pgno_t		*mt_free_pgs;
+	IDL			mt_free_pgs;
 	union {
 		ID2L	dirty_list;	/**< modified pages */
 		MDB_reader	*reader;	/**< this thread's slot in the reader table */
@@ -728,6 +722,15 @@ struct MDB_txn {
 	MDB_dbx		*mt_dbxs;
 	/** Array of MDB_db records for each known DB */
 	MDB_db		*mt_dbs;
+/** @defgroup mt_dbflag	Transaction DB Flags
+ *	@ingroup internal
+ * @{
+ */
+#define DB_DIRTY	0x01		/**< DB was written in this txn */
+#define DB_STALE	0x02		/**< DB record is older than txnID */
+/** @} */
+	/** 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.
 	 */
@@ -767,6 +770,8 @@ struct MDB_cursor {
 	MDB_db		*mc_db;
 	/** The database auxiliary record for this cursor */
 	MDB_dbx		*mc_dbx;
+	/** The @ref mt_dbflag for this database */
+	unsigned char	*mc_dbflag;
 	unsigned short 	mc_snum;	/**< number of pushed pages */
 	unsigned short	mc_top;		/**< index of top page, mc_snum-1 */
 /** @defgroup mdb_cursor	Cursor Flags
@@ -794,6 +799,8 @@ typedef struct MDB_xcursor {
 	MDB_db	mx_db;
 	/**	The auxiliary DB record for this Dup DB */
 	MDB_dbx	mx_dbx;
+	/** The @ref mt_dbflag for this Dup DB */
+	unsigned char mx_dbflag;
 } MDB_xcursor;
 
 	/** A set of pages freed by an earlier transaction. */
@@ -830,13 +837,14 @@ struct MDB_env {
 	pgno_t		me_maxpg;		/**< me_mapsize / me_psize */
 	unsigned int	me_psize;	/**< size of a page, from #GET_PAGESIZE */
 	unsigned int	me_db_toggle;	/**< which DB table is current */
+	txnid_t		me_wtxnid;		/**< ID of last txn we committed */
 	MDB_dbx		*me_dbxs;		/**< array of static DB info */
 	MDB_db		*me_dbs[2];		/**< two arrays of MDB_db info */
 	MDB_oldpages *me_pghead;	/**< list of old page records */
 	pthread_key_t	me_txkey;	/**< thread-key for readers */
 	MDB_page	*me_dpages;		/**< list of malloc'd blocks for re-use */
 	/** IDL of pages that became unused in a write txn */
-	pgno_t		me_free_pgs[MDB_IDL_UM_SIZE];
+	IDL			me_free_pgs;
 	/** ID2L of pages that were written during a write txn */
 	ID2			me_dirty_list[MDB_IDL_UM_SIZE];
 	/** rwlock for the DB tables, if #LAZY_LOCKS is false */
@@ -899,6 +907,7 @@ static void	mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcurs
 static void	mdb_xcursor_init0(MDB_cursor *mc);
 static void	mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node);
 
+static int	mdb_drop0(MDB_cursor *mc, int subs);
 static void mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi);
 
 /** @cond */
@@ -1126,7 +1135,7 @@ mdb_page_touch(MDB_cursor *mc)
 			return ENOMEM;
 		DPRINTF("touched db %u page %zu -> %zu", mc->mc_dbi, mp->mp_pgno, np->mp_pgno);
 		assert(mp->mp_pgno != np->mp_pgno);
-		mdb_midl_append(mc->mc_txn->mt_free_pgs, mp->mp_pgno);
+		mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
 		pgno = np->mp_pgno;
 		memcpy(np, mp, mc->mc_txn->mt_env->me_psize);
 		mp = np;
@@ -1167,6 +1176,7 @@ static inline int
 mdb_txn_renew0(MDB_txn *txn)
 {
 	MDB_env *env = txn->mt_env;
+	char mt_dbflag = 0;
 
 	if (txn->mt_flags & MDB_TXN_RDONLY) {
 		MDB_reader *r = pthread_getspecific(env->me_txkey);
@@ -1191,14 +1201,22 @@ mdb_txn_renew0(MDB_txn *txn)
 			r = &env->me_txns->mti_readers[i];
 			pthread_setspecific(env->me_txkey, r);
 		}
-		txn->mt_txnid = env->me_txns->mti_txnid;
 		txn->mt_toggle = env->me_txns->mti_me_toggle;
+		txn->mt_txnid = env->me_txns->mti_txnid;
+		/* This happens if a different process was the
+		 * last writer to the DB.
+		 */
+		if (env->me_wtxnid < txn->mt_txnid)
+			mt_dbflag = DB_STALE;
 		r->mr_txnid = txn->mt_txnid;
 		txn->mt_u.reader = r;
 	} else {
 		LOCK_MUTEX_W(env);
 
-		txn->mt_txnid = env->me_txns->mti_txnid+1;
+		txn->mt_txnid = env->me_txns->mti_txnid;
+		if (env->me_wtxnid < txn->mt_txnid)
+			mt_dbflag = DB_STALE;
+		txn->mt_txnid++;
 		txn->mt_toggle = env->me_txns->mti_me_toggle;
 		txn->mt_u.dirty_list = env->me_dirty_list;
 		txn->mt_u.dirty_list[0].mid = 0;
@@ -1218,6 +1236,8 @@ mdb_txn_renew0(MDB_txn *txn)
 			(txn->mt_numdbs - 2) * sizeof(MDB_db));
 	LAZY_RWLOCK_UNLOCK(&env->me_dblock);
 
+	memset(txn->mt_dbflags, mt_dbflag, env->me_numdbs);
+
 	return MDB_SUCCESS;
 }
 
@@ -1253,7 +1273,8 @@ mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **ret)
 		DPUTS("environment had fatal error, must shutdown!");
 		return MDB_PANIC;
 	}
-	if ((txn = calloc(1, sizeof(MDB_txn) + env->me_maxdbs * sizeof(MDB_db))) == NULL) {
+	if ((txn = calloc(1, sizeof(MDB_txn) +
+		env->me_maxdbs * (sizeof(MDB_db)+1))) == NULL) {
 		DPRINTF("calloc: %s", strerror(ErrCode()));
 		return ENOMEM;
 	}
@@ -1261,6 +1282,7 @@ mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **ret)
 	if (flags & MDB_RDONLY) {
 		txn->mt_flags |= MDB_TXN_RDONLY;
 	}
+	txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
 	txn->mt_env = env;
 
 	rc = mdb_txn_renew0(txn);
@@ -1289,9 +1311,11 @@ mdb_txn_reset0(MDB_txn *txn)
 	} else {
 		MDB_oldpages *mop;
 		MDB_page *dp;
-		MDB_dbi dbi;
 		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;
@@ -1310,8 +1334,6 @@ mdb_txn_reset0(MDB_txn *txn)
 		}
 
 		env->me_txn = NULL;
-		for (dbi=2; dbi<env->me_numdbs; dbi++)
-			env->me_dbxs[dbi].md_dirty = 0;
 		/* The writer mutex was locked in mdb_txn_begin. */
 		UNLOCK_MUTEX_W(env);
 	}
@@ -1362,6 +1384,23 @@ mdb_txn_commit(MDB_txn *txn)
 	env = txn->mt_env;
 
 	if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
+		if (txn->mt_numdbs > env->me_numdbs) {
+			/* update the DB tables */
+			int toggle = !env->me_db_toggle;
+			MDB_db *ip, *jp;
+			MDB_dbi i;
+
+			ip = &env->me_dbs[toggle][env->me_numdbs];
+			jp = &txn->mt_dbs[env->me_numdbs];
+			LAZY_RWLOCK_WRLOCK(&env->me_dblock);
+			for (i = env->me_numdbs; i < txn->mt_numdbs; i++) {
+				*ip++ = *jp++;
+			}
+
+			env->me_db_toggle = toggle;
+			env->me_numdbs = txn->mt_numdbs;
+			LAZY_RWLOCK_UNLOCK(&env->me_dblock);
+		}
 		mdb_txn_abort(txn);
 		return MDB_SUCCESS;
 	}
@@ -1430,6 +1469,8 @@ mdb_txn_commit(MDB_txn *txn)
 				return rc;
 			}
 		} while (i != txn->mt_free_pgs[0]);
+		if (mdb_midl_shrink(&txn->mt_free_pgs))
+			env->me_free_pgs = txn->mt_free_pgs;
 	}
 	/* should only be one record now */
 	if (env->me_pghead) {
@@ -1456,7 +1497,7 @@ mdb_txn_commit(MDB_txn *txn)
 
 		mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
 		for (i = 2; i < txn->mt_numdbs; i++) {
-			if (txn->mt_dbxs[i].md_dirty) {
+			if (txn->mt_dbflags[i] & DB_DIRTY) {
 				data.mv_data = &txn->mt_dbs[i];
 				mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
 			}
@@ -1578,6 +1619,7 @@ mdb_txn_commit(MDB_txn *txn)
 	}
 
 done:
+	env->me_wtxnid = txn->mt_txnid;
 	env->me_txn = NULL;
 	/* update the DB tables */
 	{
@@ -1594,10 +1636,6 @@ done:
 			ip++; jp++;
 		}
 
-		for (i = 2; i < txn->mt_numdbs; i++) {
-			if (txn->mt_dbxs[i].md_dirty)
-				txn->mt_dbxs[i].md_dirty = 0;
-		}
 		env->me_db_toggle = toggle;
 		env->me_numdbs = txn->mt_numdbs;
 		LAZY_RWLOCK_UNLOCK(&env->me_dblock);
@@ -1834,6 +1872,11 @@ mdb_env_create(MDB_env **env)
 	if (!e)
 		return ENOMEM;
 
+	e->me_free_pgs = mdb_midl_alloc();
+	if (!e->me_free_pgs) {
+		free(e);
+		return ENOMEM;
+	}
 	e->me_maxreaders = DEFAULT_READERS;
 	e->me_maxdbs = 2;
 	e->me_fd = INVALID_HANDLE_VALUE;
@@ -2457,6 +2500,7 @@ mdb_env_close(MDB_env *env)
 		munmap(env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo));
 	}
 	close(env->me_lfd);
+	mdb_midl_free(env->me_free_pgs);
 	free(env);
 }
 
@@ -2825,16 +2869,32 @@ mdb_page_search(MDB_cursor *mc, MDB_val *key, int modify)
 	DPRINTF("db %u root page %zu has flags 0x%X",
 		mc->mc_dbi, root, mc->mc_pg[0]->mp_flags);
 
-	if (modify) {
-		/* For sub-databases, update main root first */
-		if (mc->mc_dbi > MAIN_DBI && !mc->mc_dbx->md_dirty) {
+	/* For sub-databases, update main root first */
+	if (mc->mc_dbi > MAIN_DBI) {
+		if ((*mc->mc_dbflag & DB_STALE) ||
+			(modify && !(*mc->mc_dbflag & DB_DIRTY))) {
 			MDB_cursor mc2;
+			unsigned char dbflag = 0;
 			mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
-			rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 1);
+			rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, modify);
 			if (rc)
 				return rc;
-			mc->mc_dbx->md_dirty = 1;
+			if (*mc->mc_dbflag & DB_STALE) {
+				MDB_val data;
+				int exact = 0;
+				MDB_node *leaf = mdb_node_search(&mc2,
+					&mc->mc_dbx->md_name, &exact);
+				if (!exact)
+					return MDB_NOTFOUND;
+				mdb_node_read(mc->mc_txn, leaf, &data);
+				memcpy(mc->mc_db, data.mv_data, sizeof(MDB_db));
+			}
+			if (modify)
+				dbflag = DB_DIRTY;
+			*mc->mc_dbflag = dbflag;
 		}
+	}
+	if (modify) {
 		if (!F_ISSET(mc->mc_pg[0]->mp_flags, P_DIRTY)) {
 			if ((rc = mdb_page_touch(mc)))
 				return rc;
@@ -3475,13 +3535,13 @@ mdb_cursor_touch(MDB_cursor *mc)
 {
 	int rc;
 
-	if (mc->mc_dbi > MAIN_DBI && !mc->mc_dbx->md_dirty) {
+	if (mc->mc_dbi > MAIN_DBI && !(*mc->mc_dbflag & DB_DIRTY)) {
 		MDB_cursor mc2;
 		mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
 		rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 1);
 		if (rc)
 			 return rc;
-		mc->mc_dbx->md_dirty = 1;
+		*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)) {
@@ -3502,7 +3562,7 @@ int
 mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
     unsigned int flags)
 {
-	MDB_node	*leaf;
+	MDB_node	*leaf = NULL;
 	MDB_val	xdata, *rdata, dkey;
 	MDB_page	*fp;
 	MDB_db dummy;
@@ -3536,7 +3596,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 		mdb_cursor_push(mc, np);
 		mc->mc_db->md_root = np->mp_pgno;
 		mc->mc_db->md_depth++;
-		mc->mc_dbx->md_dirty = 1;
+		*mc->mc_dbflag = DB_DIRTY;
 		if ((mc->mc_db->md_flags & (MDB_DUPSORT|MDB_DUPFIXED))
 			== MDB_DUPFIXED)
 			np->mp_flags |= P_LEAF2;
@@ -3799,45 +3859,10 @@ mdb_cursor_del(MDB_cursor *mc, unsigned int flags)
 
 		if (leaf->mn_flags & F_SUBDATA) {
 			/* add all the child DB's pages to the free list */
-			rc = mdb_page_search(&mc->mc_xcursor->mx_cursor, NULL, 0);
+			rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
 			if (rc == MDB_SUCCESS) {
-				MDB_node *ni;
-				MDB_cursor *mx;
-				unsigned int i;
-
-				mx = &mc->mc_xcursor->mx_cursor;
 				mc->mc_db->md_entries -=
-					mx->mc_db->md_entries;
-
-				mdb_cursor_pop(mx);
-				while (mx->mc_snum > 0) {
-					for (i=0; i<NUMKEYS(mx->mc_pg[mx->mc_top]); i++) {
-						pgno_t pg;
-						ni = NODEPTR(mx->mc_pg[mx->mc_top], i);
-						pg = NODEPGNO(ni);
-						/* free it */
-						mdb_midl_append(mc->mc_txn->mt_free_pgs, pg);
-					}
-					if (!mx->mc_top)
-						break;
-					rc = mdb_cursor_sibling(mx, 1);
-					if (rc) {
-						/* no more siblings, go back to beginning
-						 * of previous level. (stack was already popped
-						 * by mdb_cursor_sibling)
-						 */
-						for (i=1; i<mx->mc_top; i++) {
-							pgno_t pg;
-							ni = NODEPTR(mx->mc_pg[i-1],0);
-							pg = NODEPGNO(ni);
-							if ((rc = mdb_page_get(mc->mc_txn, pg, &mx->mc_pg[i])))
-								break;
-						}
-					}
-				}
-				/* free it */
-				mdb_midl_append(mc->mc_txn->mt_free_pgs,
-					mx->mc_db->md_root);
+					mc->mc_xcursor->mx_db.md_entries;
 			}
 		}
 	}
@@ -4181,11 +4206,10 @@ mdb_xcursor_init0(MDB_cursor *mc)
 	mx->mx_cursor.mc_db = &mx->mx_db;
 	mx->mx_cursor.mc_dbx = &mx->mx_dbx;
 	mx->mx_cursor.mc_dbi = mc->mc_dbi+1;
-	mx->mx_dbx.md_parent = mc->mc_dbi;
+	mx->mx_cursor.mc_dbflag = &mx->mx_dbflag;
 	mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
 	mx->mx_dbx.md_dcmp = NULL;
 	mx->mx_dbx.md_rel = mc->mc_dbx->md_rel;
-	mx->mx_dbx.md_dirty = 0;
 }
 
 /** Final setup of a sorted-dups cursor.
@@ -4228,8 +4252,8 @@ mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node)
 	}
 	DPRINTF("Sub-db %u for db %u root page %zu", mx->mx_cursor.mc_dbi, mc->mc_dbi,
 		mx->mx_db.md_root);
-	if (F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY))
-		mx->mx_dbx.md_dirty = 1;
+	mx->mx_dbflag = (F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY)) ?
+		DB_DIRTY : 0;
 	mx->mx_dbx.md_name.mv_data = NODEKEY(node);
 	mx->mx_dbx.md_name.mv_size = node->mn_ksize;
 	if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
@@ -4244,6 +4268,7 @@ mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx)
 	mc->mc_txn = txn;
 	mc->mc_db = &txn->mt_dbs[dbi];
 	mc->mc_dbx = &txn->mt_dbxs[dbi];
+	mc->mc_dbflag = &txn->mt_dbflags[dbi];
 	mc->mc_snum = 0;
 	mc->mc_flags = 0;
 	if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
@@ -4535,7 +4560,7 @@ mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
 			return rc;
 	}
 
-	mdb_midl_append(csrc->mc_txn->mt_free_pgs, csrc->mc_pg[csrc->mc_top]->mp_pgno);
+	mdb_midl_append(&csrc->mc_txn->mt_free_pgs, csrc->mc_pg[csrc->mc_top]->mp_pgno);
 	if (IS_LEAF(csrc->mc_pg[csrc->mc_top]))
 		csrc->mc_db->md_leaf_pages--;
 	else
@@ -4597,11 +4622,11 @@ mdb_rebalance(MDB_cursor *mc)
 			mc->mc_db->md_root = P_INVALID;
 			mc->mc_db->md_depth = 0;
 			mc->mc_db->md_leaf_pages = 0;
-			mdb_midl_append(mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
+			mdb_midl_append(&mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
 			mc->mc_snum = 0;
 		} else if (IS_BRANCH(mc->mc_pg[mc->mc_top]) && NUMKEYS(mc->mc_pg[mc->mc_top]) == 1) {
 			DPUTS("collapsing root page!");
-			mdb_midl_append(mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
+			mdb_midl_append(&mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
 			mc->mc_db->md_root = NODEPGNO(NODEPTR(mc->mc_pg[mc->mc_top], 0));
 			if ((rc = mdb_page_get(mc->mc_txn, mc->mc_db->md_root,
 				&mc->mc_pg[mc->mc_top])))
@@ -4685,7 +4710,7 @@ mdb_cursor_del0(MDB_cursor *mc, MDB_node *leaf)
 		ovpages = OVPAGES(NODEDSZ(leaf), mc->mc_txn->mt_env->me_psize);
 		for (i=0; i<ovpages; i++) {
 			DPRINTF("freed ov page %zu", pg);
-			mdb_midl_append(mc->mc_txn->mt_free_pgs, pg);
+			mdb_midl_append(&mc->mc_txn->mt_free_pgs, pg);
 			pg++;
 		}
 	}
@@ -5152,7 +5177,7 @@ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 {
 	MDB_val key, data;
 	MDB_dbi i;
-	int rc, dirty = 0;
+	int rc, dbflag = 0;
 	size_t len;
 
 	if (txn->mt_dbxs[FREE_DBI].md_cmp == NULL) {
@@ -5201,7 +5226,7 @@ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 		dummy.md_flags = flags & 0xffff;
 		mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
 		rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
-		dirty = 1;
+		dbflag = DB_DIRTY;
 	}
 
 	/* OK, got info, add to table */
@@ -5209,8 +5234,7 @@ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 		txn->mt_dbxs[txn->mt_numdbs].md_name.mv_data = strdup(name);
 		txn->mt_dbxs[txn->mt_numdbs].md_name.mv_size = len;
 		txn->mt_dbxs[txn->mt_numdbs].md_rel = NULL;
-		txn->mt_dbxs[txn->mt_numdbs].md_parent = MAIN_DBI;
-		txn->mt_dbxs[txn->mt_numdbs].md_dirty = dirty;
+		txn->mt_dbflags[txn->mt_numdbs] = dbflag;
 		memcpy(&txn->mt_dbs[txn->mt_numdbs], data.mv_data, sizeof(MDB_db));
 		*dbi = txn->mt_numdbs;
 		txn->mt_env->me_dbs[0][txn->mt_numdbs] = txn->mt_dbs[txn->mt_numdbs];
@@ -5230,17 +5254,103 @@ int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
 	return mdb_stat0(txn->mt_env, &txn->mt_dbs[dbi], arg);
 }
 
-void mdb_close(MDB_txn *txn, MDB_dbi dbi)
+void mdb_close(MDB_env *env, MDB_dbi dbi)
 {
 	char *ptr;
-	if (dbi <= MAIN_DBI || dbi >= txn->mt_numdbs)
+	if (dbi <= MAIN_DBI || dbi >= env->me_numdbs)
 		return;
-	ptr = txn->mt_dbxs[dbi].md_name.mv_data;
-	txn->mt_dbxs[dbi].md_name.mv_data = NULL;
-	txn->mt_dbxs[dbi].md_name.mv_size = 0;
+	ptr = env->me_dbxs[dbi].md_name.mv_data;
+	env->me_dbxs[dbi].md_name.mv_data = NULL;
+	env->me_dbxs[dbi].md_name.mv_size = 0;
 	free(ptr);
 }
 
+/** Add all the DB's pages to the free list.
+ * @param[in] mc Cursor on the DB to free.
+ * @param[in] subs non-Zero to check for sub-DBs in this DB.
+ * @return 0 on success, non-zero on failure.
+ */
+static int
+mdb_drop0(MDB_cursor *mc, int subs)
+{
+	int rc;
+
+	rc = mdb_page_search(mc, NULL, 0);
+	if (rc == MDB_SUCCESS) {
+		MDB_node *ni;
+		MDB_cursor mx;
+		unsigned int i;
+
+		/* LEAF2 pages have no nodes, cannot have sub-DBs */
+		if (!subs || IS_LEAF2(mc->mc_pg[mc->mc_top]))
+			mdb_cursor_pop(mc);
+
+		mdb_cursor_copy(mc, &mx);
+		while (mc->mc_snum > 0) {
+			if (IS_LEAF(mc->mc_pg[mc->mc_top])) {
+				for (i=0; i<NUMKEYS(mc->mc_pg[mc->mc_top]); i++) {
+					ni = NODEPTR(mc->mc_pg[mc->mc_top], i);
+					if (ni->mn_flags & F_SUBDATA) {
+						mdb_xcursor_init1(mc, ni);
+						rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
+						if (rc)
+							return rc;
+					}
+				}
+			} else {
+				for (i=0; i<NUMKEYS(mc->mc_pg[mc->mc_top]); i++) {
+					pgno_t pg;
+					ni = NODEPTR(mc->mc_pg[mc->mc_top], i);
+					pg = NODEPGNO(ni);
+					/* free it */
+					mdb_midl_append(&mc->mc_txn->mt_free_pgs, pg);
+				}
+			}
+			if (!mc->mc_top)
+				break;
+			rc = mdb_cursor_sibling(mc, 1);
+			if (rc) {
+				/* no more siblings, go back to beginning
+				 * of previous level. (stack was already popped
+				 * by mdb_cursor_sibling)
+				 */
+				for (i=1; i<mc->mc_top; i++)
+					mc->mc_pg[i] = mx.mc_pg[i];
+			}
+		}
+		/* free it */
+		mdb_midl_append(&mc->mc_txn->mt_free_pgs,
+			mc->mc_db->md_root);
+	}
+	return 0;
+}
+
+int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
+{
+	MDB_cursor *mc;
+	int rc;
+
+	if (!txn || !dbi || dbi >= txn->mt_numdbs)
+		return EINVAL;
+
+	rc = mdb_cursor_open(txn, dbi, &mc);
+	if (rc)
+		return rc;
+
+	rc = mdb_drop0(mc, 1);
+	if (rc)
+		mdb_cursor_close(mc);
+		return rc;
+
+	if (del) {
+		rc = mdb_del(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL);
+		if (!rc)
+			mdb_close(txn->mt_env, dbi);
+	}
+	mdb_cursor_close(mc);
+	return rc;
+}
+
 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
 {
 	if (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
diff --git a/libraries/libmdb/mdb.h b/libraries/libmdb/mdb.h
index b99ece7c95..18d73681ea 100644
--- a/libraries/libmdb/mdb.h
+++ b/libraries/libmdb/mdb.h
@@ -531,7 +531,9 @@ void mdb_txn_reset(MDB_txn *txn);
 int  mdb_txn_renew(MDB_txn *txn);
 
 	/** Open a database in the environment.
-	 * The database handle may be discarded by calling #mdb_close().
+	 * 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.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 	 * @param[in] name The name of the database to open. If only a single
 	 * 	database is needed in the enviroment, this value may be NULL.
@@ -592,15 +594,29 @@ 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.
-	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+	 * 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.
+	 * @param[in] env An environment handle returned by #mdb_env_create()
 	 * @param[in] dbi A database handle returned by #mdb_open()
 	 */
-void mdb_close(MDB_txn *txn, MDB_dbi dbi);
+void mdb_close(MDB_env *env, MDB_dbi dbi);
+
+	/** 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()
+	 * @param[in] dbi A database handle returned by #mdb_open()
+	 * @param[in] del non-zero to delete the DB from the environment,
+	 * otherwise just free its pages.
+	 * @return A non-zero error value on failure and 0 on success.
+	 */
+int  mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
 
 	/** 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 special key flags were specified
+	 * If no comparison function is specified, and no speAGAINcial key flags were specified
 	 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
 	 * before longer keys.
 	 * @warning This function must be called before any data access functions are used,
diff --git a/libraries/libmdb/mdb_stat.c b/libraries/libmdb/mdb_stat.c
index 4bcdb92fa6..931ec61a58 100644
--- a/libraries/libmdb/mdb_stat.c
+++ b/libraries/libmdb/mdb_stat.c
@@ -56,7 +56,7 @@ int main(int argc,char * argv[])
 	printf("Leaf pages: %zu\n", mst.ms_leaf_pages);
 	printf("Overflow pages: %zu\n", mst.ms_overflow_pages);
 	printf("Entries: %zu\n", mst.ms_entries);
-	mdb_close(txn, dbi);
+	mdb_close(env, dbi);
 	mdb_txn_abort(txn);
 	mdb_env_close(env);
 
diff --git a/libraries/libmdb/midl.c b/libraries/libmdb/midl.c
index 7a7b59c7c0..70487aa3d9 100644
--- a/libraries/libmdb/midl.c
+++ b/libraries/libmdb/midl.c
@@ -17,6 +17,7 @@
 
 #include <limits.h>
 #include <string.h>
+#include <stdlib.h>
 #include <sys/types.h>
 #include <assert.h>
 #include "midl.h"
@@ -117,11 +118,44 @@ int mdb_midl_insert( IDL ids, ID id )
 }
 #endif
 
-int mdb_midl_append( IDL ids, ID id )
+IDL mdb_midl_alloc()
 {
+	IDL ids = malloc((MDB_IDL_UM_MAX+1) * sizeof(ID));
+	*ids++ = MDB_IDL_UM_MAX;
+	return ids;
+}
+
+void mdb_midl_free(IDL ids)
+{
+	free(ids-1);
+}
+
+int mdb_midl_shrink( IDL *idp )
+{
+	IDL ids = *idp;
+	if (ids[-1] > MDB_IDL_UM_MAX) {
+		ids = realloc(ids, (MDB_IDL_UM_MAX+1) * sizeof(ID));
+		*ids++ = MDB_IDL_UM_MAX;
+		*idp = ids;
+		return 1;
+	}
+	return 0;
+}
+
+int mdb_midl_append( IDL *idp, ID id )
+{
+	IDL ids = *idp;
 	/* Too big? */
-	if (ids[0] >= MDB_IDL_UM_MAX)
-		return -1;
+	if (ids[0] >= ids[-1]) {
+		IDL idn = ids-1;
+		/* grow it */
+		idn = realloc(idn, (*idn + MDB_IDL_UM_MAX + 1) * sizeof(ID));
+		if (!idn)
+			return -1;
+		*idn++ += MDB_IDL_UM_MAX;
+		ids = idn;
+		*idp = ids;
+	}
 	ids[0]++;
 	ids[ids[0]] = id;
 	return 0;
diff --git a/libraries/libmdb/midl.h b/libraries/libmdb/midl.h
index 041aa03b3a..0ab89e0333 100644
--- a/libraries/libmdb/midl.h
+++ b/libraries/libmdb/midl.h
@@ -111,12 +111,30 @@ typedef ID *IDL;
 int mdb_midl_insert( IDL ids, ID id );
 #endif
 
+	/** Allocate an IDL.
+	 * Allocates memory for an IDL of a default size.
+	 * @return	IDL on success, NULL on failure.
+	 */
+IDL mdb_midl_alloc();
+
+	/** Free an IDL.
+	 * @param[in] ids	The IDL to free.
+	 */
+void mdb_midl_free(IDL ids);
+
+	/** Shrink an IDL.
+	 * Return the IDL to the default size if it has grown larger.
+	 * @param[in,out] idp	Address of the IDL to shrink.
+	 * @return	0 on no change, non-zero if shrunk.
+	 */
+int mdb_midl_shrink(IDL *idp);
+
 	/** Append an ID onto an IDL.
-	 * @param[in,out] ids	The IDL to append to.
+	 * @param[in,out] idp	Address of the IDL to append to.
 	 * @param[in] id	The ID to append.
 	 * @return	0 on success, -2 if the IDL is too large.
 	 */
-int mdb_midl_append( IDL ids, ID id );
+int mdb_midl_append( IDL *idp, ID id );
 
 	/** Sort an IDL.
 	 * @param[in,out] ids	The IDL to sort.
diff --git a/libraries/libmdb/mtest.c b/libraries/libmdb/mtest.c
index 8f2ecbf0e9..89f0ac4643 100644
--- a/libraries/libmdb/mtest.c
+++ b/libraries/libmdb/mtest.c
@@ -146,7 +146,7 @@ int main(int argc,char * argv[])
 		}
 #endif
 		mdb_cursor_close(cursor);
-		mdb_close(txn, dbi);
+		mdb_close(env, dbi);
 
 		mdb_txn_abort(txn);
 		mdb_env_close(env);
diff --git a/libraries/libmdb/mtest2.c b/libraries/libmdb/mtest2.c
index 5aeb97d3d4..17c1ecfe59 100644
--- a/libraries/libmdb/mtest2.c
+++ b/libraries/libmdb/mtest2.c
@@ -108,7 +108,7 @@ int main(int argc,char * argv[])
 			(int) data.mv_size, (char *) data.mv_data);
 	}
 	mdb_cursor_close(cursor);
-	mdb_close(txn, dbi);
+	mdb_close(env, dbi);
 
 	mdb_txn_abort(txn);
 	mdb_env_close(env);
diff --git a/libraries/libmdb/mtest3.c b/libraries/libmdb/mtest3.c
index 467a12352d..43e34817b9 100644
--- a/libraries/libmdb/mtest3.c
+++ b/libraries/libmdb/mtest3.c
@@ -118,7 +118,7 @@ int main(int argc,char * argv[])
 			(int) data.mv_size, (char *) data.mv_data);
 	}
 	mdb_cursor_close(cursor);
-	mdb_close(txn, dbi);
+	mdb_close(env, dbi);
 
 	mdb_txn_abort(txn);
 	mdb_env_close(env);
diff --git a/libraries/libmdb/mtest4.c b/libraries/libmdb/mtest4.c
index d3a7877417..821055ad7c 100644
--- a/libraries/libmdb/mtest4.c
+++ b/libraries/libmdb/mtest4.c
@@ -152,7 +152,7 @@ int main(int argc,char * argv[])
 			(int) data.mv_size, (char *) data.mv_data);
 	}
 	mdb_cursor_close(cursor);
-	mdb_close(txn, dbi);
+	mdb_close(env, dbi);
 
 	mdb_txn_abort(txn);
 	mdb_env_close(env);
diff --git a/libraries/libmdb/mtest5.c b/libraries/libmdb/mtest5.c
index 472b100756..5fb6bb0618 100644
--- a/libraries/libmdb/mtest5.c
+++ b/libraries/libmdb/mtest5.c
@@ -120,7 +120,7 @@ int main(int argc,char * argv[])
 			(int) data.mv_size, (char *) data.mv_data);
 	}
 	mdb_cursor_close(cursor);
-	mdb_close(txn, dbi);
+	mdb_close(env, dbi);
 
 	mdb_txn_abort(txn);
 	mdb_env_close(env);