diff --git a/.hgignore b/.hgignore
index ee5f68e..0df4e77 100644
--- a/.hgignore
+++ b/.hgignore
@@ -8,6 +8,7 @@ spec/\.status
 coverage/
 vendor/
 pkg/
+^tags$
 ^Session.vim$
 ^Makefile$
 
diff --git a/.pryrc b/.pryrc
index 3088e92..8765b2e 100644
--- a/.pryrc
+++ b/.pryrc
@@ -11,5 +11,6 @@ rescue Exception => e
 		e.backtrace.join( "\n\t" )
 end
 
-db = MDBX::Database.open( 'tmp/testdb', max_collections: 100 )
+db = MDBX::Database.open( 'tmp/testdb', max_collections: 50 )
+#db = MDBX::Database.open( 'tmp/testdb', duplicate_keys: true )
 
diff --git a/History.md b/History.md
index a04d58c..8133d01 100644
--- a/History.md
+++ b/History.md
@@ -1,5 +1,14 @@
 # Release History for MDBX
 
+---
+## v0.3.1 [2021-05-16] Mahlon E. Smith <mahlon@martini.nu>
+
+Bugfix:
+
+ - #drop could potentially remove unintended data.  Yanked version
+   v0.3.0.
+
+
 ---
 ## v0.3.0 [2021-04-09] Mahlon E. Smith <mahlon@martini.nu>
 
diff --git a/README.md b/README.md
index 90757a7..e517bda 100644
--- a/README.md
+++ b/README.md
@@ -340,13 +340,6 @@ information about the build environment, the database environment, and
 the currently connected clients.
 
 
-## TODO
-
-  - Expose more database/collection information to statistics
-  - Support libmdbx multiple values per key DUPSORT via `put`, `get`
-    Enumerators, and a 'value' argument for `delete`.
-
-
 ## Contributing
 
 You can check out the current development source with Mercurial via its
diff --git a/experiments/thread_usage.rb b/experiments/thread_usage.rb
index bac77ff..9a21746 100755
--- a/experiments/thread_usage.rb
+++ b/experiments/thread_usage.rb
@@ -37,7 +37,6 @@ def run_bench( db, msg )
 			threads.map( &:join )
 		end
 
-
 		# Long running transactions require a mutex across threads.
 		#
 		x.report( "txn per thread:" ) do
@@ -78,4 +77,3 @@ run_bench( db, "Default database flags:" )
 db = MDBX::Database.open( 'tmpdb', no_metasync: true )
 run_bench( db, "Disabled metasync:" )
 
-
diff --git a/ext/mdbx_ext/database.c b/ext/mdbx_ext/database.c
index e8ef676..32f09f6 100644
--- a/ext/mdbx_ext/database.c
+++ b/ext/mdbx_ext/database.c
@@ -1,21 +1,16 @@
-/* vim: set noet sta sw=4 ts=4 : */
+/* vim: set noet sta sw=4 ts=4 fdm=marker: */
+/*
+ * Primary database handle functions.
+ *
+ */
 
 #include "mdbx_ext.h"
 
-/* Shortcut for fetching current DB variables.
- */
-#define UNWRAP_DB( val, db ) \
-	rmdbx_db_t *db; \
-	TypedData_Get_Struct( val, rmdbx_db_t, &rmdbx_db_data, db )
-
-#define CHECK_HANDLE \
-	if ( ! db->state.open ) rb_raise( rmdbx_eDatabaseError, "Closed database." )
-
-
 VALUE rmdbx_cDatabase;
 
+
 /*
- * Ruby allocation hook.
+ * Ruby data allocation wrapper.
  */
 static const rb_data_type_t rmdbx_db_data = {
 	.wrap_struct_name = "MDBX::Database::Data",
@@ -30,11 +25,24 @@ static const rb_data_type_t rmdbx_db_data = {
 VALUE
 rmdbx_alloc( VALUE klass )
 {
-	rmdbx_db_t *new = RB_ALLOC( rmdbx_db_t );
+	rmdbx_db_t *new;
 	return TypedData_Make_Struct( klass, rmdbx_db_t, &rmdbx_db_data, new );
 }
 
 
+/*
+ * Cleanup a previously allocated DB environment.
+ */
+void
+rmdbx_free( void *db )
+{
+	if ( db ) {
+		rmdbx_close_all( db );
+		xfree( db );
+	}
+}
+
+
 /*
  * Ensure all database file descriptors are collected and
  * removed.
@@ -65,19 +73,9 @@ rmdbx_close_dbi( rmdbx_db_t *db )
 
 
 /*
- * Cleanup a previously allocated DB environment.
- */
-void
-rmdbx_free( void *db )
-{
-	if ( db ) {
-		rmdbx_close_all( db );
-		xfree( db );
-	}
-}
-
-
-/*
+ * call-seq:
+ *    db.close => true
+ *
  * Cleanly close an opened database.
  */
 VALUE
@@ -104,17 +102,63 @@ rmdbx_closed_p( VALUE self )
 
 
 /*
- * call-seq:
- *    db.in_transaction? => false
+ * Check if a given +flag+ is enabled for flag +val+.
+ */
+int
+rmdbx_flag_enabled( val, flag )
+{
+	return ( val & flag ) == flag;
+}
+
+
+/*
+ * Given a ruby string +key+ and a pointer to an MDBX_val, prepare the
+ * key for usage within mdbx.  All keys are explicitly converted to
+ * strings.
  *
- * Predicate: return true if a transaction (or snapshot)
- * is currently open.
+ */
+void
+rmdbx_key_for( VALUE key, MDBX_val *ckey )
+{
+	VALUE key_str  = rb_funcall( key, rb_intern("to_s"), 0 );
+	ckey->iov_len  = RSTRING_LEN( key_str );
+	ckey->iov_base = malloc( ckey->iov_len );
+	strlcpy( ckey->iov_base, StringValuePtr(key_str), ckey->iov_len + 1 );
+}
+
+
+/*
+ * Given a ruby +value+ and a pointer to an MDBX_val, prepare
+ * the value for usage within mdbx.  Values are potentially serialized.
+ *
+ */
+void
+rmdbx_val_for( VALUE self, VALUE val, MDBX_val *data )
+{
+	VALUE serialize_proc = rb_iv_get( self, "@serializer" );
+
+	if ( ! NIL_P( serialize_proc ) )
+		val = rb_funcall( serialize_proc, rb_intern("call"), 1, val );
+
+	Check_Type( val, T_STRING );
+
+	data->iov_len  = RSTRING_LEN( val );
+	data->iov_base = malloc( data->iov_len );
+	strlcpy( data->iov_base, StringValuePtr(val), data->iov_len + 1 );
+}
+
+
+/*
+ * Deserialize and return a value.
  */
 VALUE
-rmdbx_in_transaction_p( VALUE self )
+rmdbx_deserialize( VALUE self, VALUE val )
 {
-	UNWRAP_DB( self, db );
-	return db->txn ? Qtrue : Qfalse;
+	VALUE deserialize_proc = rb_iv_get( self, "@deserializer" );
+	if ( ! NIL_P( deserialize_proc ) )
+		val = rb_funcall( deserialize_proc, rb_intern("call"), 1, val );
+
+	return val;
 }
 
 
@@ -151,122 +195,8 @@ rmdbx_open_env( VALUE self )
 		rmdbx_close_all( db );
 		rb_raise( rmdbx_eDatabaseError, "mdbx_env_open: (%d) %s", rc, mdbx_strerror(rc) );
 	}
+
 	db->state.open = 1;
-
-	return Qtrue;
-}
-
-
-/*
- * Open a cursor for iteration.
- */
-void
-rmdbx_open_cursor( rmdbx_db_t *db )
-{
-	CHECK_HANDLE;
-	if ( ! db->txn ) rb_raise( rmdbx_eDatabaseError, "No snapshot or transaction currently open." );
-
-	int rc = mdbx_cursor_open( db->txn, db->dbi, &db->cursor );
-	if ( rc != MDBX_SUCCESS ) {
-		rmdbx_close_all( db );
-		rb_raise( rmdbx_eDatabaseError, "Unable to open cursor: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-
-	return;
-}
-
-
-/*
- * Open a new database transaction.  If a transaction is already
- * open, this is a no-op.
- *
- * +rwflag+ must be either MDBX_TXN_RDONLY or MDBX_TXN_READWRITE.
- */
-void
-rmdbx_open_txn( rmdbx_db_t *db, int rwflag )
-{
-	if ( db->txn ) return;
-
-	int rc = mdbx_txn_begin( db->env, NULL, rwflag, &db->txn );
-	if ( rc != MDBX_SUCCESS ) {
-		rmdbx_close_all( db );
-		rb_raise( rmdbx_eDatabaseError, "mdbx_txn_begin: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-
-	if ( db->dbi == 0 ) {
-		// FIXME: dbi_flags
-		rc = mdbx_dbi_open( db->txn, db->subdb, MDBX_CREATE, &db->dbi );
-		if ( rc != MDBX_SUCCESS ) {
-			rmdbx_close_all( db );
-			rb_raise( rmdbx_eDatabaseError, "mdbx_dbi_open: (%d) %s", rc, mdbx_strerror(rc) );
-		}
-	}
-
-	return;
-}
-
-
-/*
- * Close any existing database transaction. If there is no
- * active transaction, this is a no-op.  If there is a long
- * running transaction open, this is a no-op.
- *
- * +txnflag must either be RMDBX_TXN_ROLLBACK or RMDBX_TXN_COMMIT.
- */
-void
-rmdbx_close_txn( rmdbx_db_t *db, int txnflag )
-{
-	if ( ! db->txn || db->state.retain_txn > -1 ) return;
-
-	if ( txnflag == RMDBX_TXN_COMMIT ) {
-		mdbx_txn_commit( db->txn );
-	}
-	else {
-		mdbx_txn_abort( db->txn );
-	}
-
-	db->txn = 0;
-	return;
-}
-
-
-/*
- * call-seq:
- *    db.open_transaction( mode )
- *
- * Open a new long-running transaction.  If +mode+ is true,
- * it is opened read/write.
- *
- */
-VALUE
-rmdbx_rb_opentxn( VALUE self, VALUE mode )
-{
-	UNWRAP_DB( self, db );
-	CHECK_HANDLE;
-
-	rmdbx_open_txn( db, RTEST(mode) ? MDBX_TXN_READWRITE : MDBX_TXN_RDONLY );
-	db->state.retain_txn = RTEST(mode) ? 1 : 0;
-
-	return Qtrue;
-}
-
-
-/*
- * call-seq:
- *    db.close_transaction( mode )
- *
- * Close a long-running transaction.  If +write+ is true,
- * the transaction is committed.  Otherwise, rolled back.
- *
- */
-VALUE
-rmdbx_rb_closetxn( VALUE self, VALUE write )
-{
-	UNWRAP_DB( self, db );
-
-	db->state.retain_txn = -1;
-	rmdbx_close_txn( db, RTEST(write) ? RMDBX_TXN_COMMIT : RMDBX_TXN_ROLLBACK );
-
 	return Qtrue;
 }
 
@@ -323,6 +253,7 @@ rmdbx_drop( VALUE self, VALUE name )
 	name = rb_funcall( name, rb_intern("to_s"), 0 );
 	db->subdb = StringValueCStr( name );
 
+	rmdbx_close_dbi( db ); /* ensure we're reopening within the new subdb */
 	rmdbx_open_txn( db, MDBX_TXN_READWRITE );
 	int rc = mdbx_drop( db->txn, db->dbi, true );
 
@@ -333,61 +264,319 @@ rmdbx_drop( VALUE self, VALUE name )
 
 	/* Reset the current collection to the top level. */
 	db->subdb = NULL;
+	rmdbx_close_dbi( db ); /* ensure next access is not in the defunct subdb */
+
+	return self;
+}
+
+
+/* call-seq:
+ *    db.length -> Integer
+ *
+ * Returns the count of keys in the currently selected collection.
+ */
+VALUE
+rmdbx_length( VALUE self )
+{
+	UNWRAP_DB( self, db );
+	MDBX_stat mstat;
+
+	CHECK_HANDLE();
+	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
+
+	int rc = mdbx_dbi_stat( db->txn, db->dbi, &mstat, sizeof(mstat) );
+	if ( rc != MDBX_SUCCESS )
+		rb_raise( rmdbx_eDatabaseError, "mdbx_dbi_stat: (%d) %s", rc, mdbx_strerror(rc) );
+
+	VALUE rv = LONG2FIX( mstat.ms_entries );
+	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
+
+	return rv;
+}
+
+
+/* call-seq:
+ *    db.include?( 'key' ) => bool
+ *
+ * Returns true if the current collection contains +key+.
+ */
+VALUE
+rmdbx_include( VALUE self, VALUE key )
+{
+	UNWRAP_DB( self, db );
+
+	CHECK_HANDLE();
+	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
+
+	MDBX_val ckey;
+	MDBX_val data;
+	rmdbx_key_for( key, &ckey );
+
+	int rc = mdbx_get( db->txn, db->dbi, &ckey, &data );
+	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
+	xfree( ckey.iov_base );
+
+	switch ( rc ) {
+		case MDBX_SUCCESS:
+			return Qtrue;
+
+		case MDBX_NOTFOUND:
+			return Qfalse;
+
+		default:
+			rmdbx_close( self );
+			rb_raise( rmdbx_eDatabaseError, "Unable to fetch key: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+}
+
+
+/* call-seq:
+ *    db[ 'key' ] => value
+ *
+ * Return a single value for +key+ immediately.
+ */
+VALUE
+rmdbx_get_val( VALUE self, VALUE key )
+{
+	UNWRAP_DB( self, db );
+
+	CHECK_HANDLE();
+	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
+
+	MDBX_val ckey;
+	MDBX_val data;
+
+	rmdbx_key_for( key, &ckey );
+	int rc = mdbx_get( db->txn, db->dbi, &ckey, &data );
+	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
+	xfree( ckey.iov_base );
+
+	VALUE rv;
+	switch ( rc ) {
+		case MDBX_SUCCESS:
+			rv = rb_str_new( data.iov_base, data.iov_len );
+			return rmdbx_deserialize( self, rv );
+
+		case MDBX_NOTFOUND:
+			return Qnil;
+
+		default:
+			rmdbx_close( self );
+			rb_raise( rmdbx_eDatabaseError, "Unable to fetch value: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+}
+
+
+/* call-seq:
+ *    db[ 'key' ] = value
+ *
+ * Set a single value for +key+.  If the value is +nil+, the
+ * key is removed.
+ */
+VALUE
+rmdbx_put_val( VALUE self, VALUE key, VALUE val )
+{
+	int rc;
+	UNWRAP_DB( self, db );
+
+	CHECK_HANDLE();
+	rmdbx_open_txn( db, MDBX_TXN_READWRITE );
+
+	MDBX_val ckey;
+	rmdbx_key_for( key, &ckey );
+
+	if ( NIL_P(val) ) { /* remove if set to nil */
+		rc = mdbx_del( db->txn, db->dbi, &ckey, NULL );
+	}
+	else {
+		MDBX_val old;
+		MDBX_val data;
+		rmdbx_val_for( self, val, &data );
+		rc = mdbx_replace( db->txn, db->dbi, &ckey, &data, &old, 0 );
+		xfree( data.iov_base );
+	}
+
+	rmdbx_close_txn( db, RMDBX_TXN_COMMIT );
+	xfree( ckey.iov_base );
+
+	switch ( rc ) {
+		case MDBX_SUCCESS:
+			return val;
+		case MDBX_NOTFOUND:
+			return Qnil;
+		default:
+			rb_raise( rmdbx_eDatabaseError, "Unable to update value: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+}
+
+
+/*
+ * Return the currently selected collection, or +nil+ if at the
+ * top-level.
+ */
+VALUE
+rmdbx_get_subdb( VALUE self )
+{
+	UNWRAP_DB( self, db );
+	return ( db->subdb == NULL ) ? Qnil : rb_str_new_cstr( db->subdb );
+}
+
+
+/*
+ * Sets the current collection name for read/write operations.
+ *
+ */
+VALUE
+rmdbx_set_subdb( VALUE self, VALUE name )
+{
+	UNWRAP_DB( self, db );
+
+	/* Provide a friendlier error message if max_collections is 0. */
+	if ( db->settings.max_collections == 0 )
+		rb_raise( rmdbx_eDatabaseError, "Unable to change collection: collections are not enabled." );
+
+	/* All transactions must be closed when switching database handles. */
+	if ( db->txn )
+		rb_raise( rmdbx_eDatabaseError, "Unable to change collection: transaction open" );
+
+	db->subdb = NIL_P( name ) ? NULL : StringValueCStr( name );
+
+	/* Reset the db handle and issue a single transaction to reify
+	   the collection.
+	*/
+	rmdbx_close_dbi( db );
+	rmdbx_open_txn( db, MDBX_TXN_READWRITE );
+	rmdbx_close_txn( db, RMDBX_TXN_COMMIT );
 
 	return self;
 }
 
 
 /*
- * Given a ruby +arg+, convert and return a structure
- * suitable for usage as a key for mdbx.  All keys are explicitly
- * converted to strings.
- */
-MDBX_val
-rmdbx_key_for( VALUE arg )
-{
-	MDBX_val rv;
-
-	arg = rb_funcall( arg, rb_intern("to_s"), 0 );
-	rv.iov_len  = RSTRING_LEN( arg );
-	rv.iov_base = StringValuePtr( arg );
-
-	return rv;
-}
-
-
-/*
- * Given a ruby +arg+, convert and return a structure
- * suitable for usage as a value for mdbx.
- */
-MDBX_val
-rmdbx_val_for( VALUE self, VALUE arg )
-{
-	MDBX_val rv;
-	VALUE serialize_proc;
-
-	serialize_proc = rb_iv_get( self, "@serializer" );
-	if ( ! NIL_P( serialize_proc ) )
-		arg = rb_funcall( serialize_proc, rb_intern("call"), 1, arg );
-
-	rv.iov_len  = RSTRING_LEN( arg );
-	rv.iov_base = StringValuePtr( arg );
-
-	return rv;
-}
-
-
-/*
- * Deserialize and return a value.
+ * call-seq:
+ *    db.in_transaction? => false
+ *
+ * Predicate: return true if a transaction (or snapshot)
+ * is currently open.
  */
 VALUE
-rmdbx_deserialize( VALUE self, VALUE val )
+rmdbx_in_transaction_p( VALUE self )
 {
-	VALUE deserialize_proc = rb_iv_get( self, "@deserializer" );
-	if ( ! NIL_P( deserialize_proc ) )
-		val = rb_funcall( deserialize_proc, rb_intern("call"), 1, val );
+	UNWRAP_DB( self, db );
+	return db->txn ? Qtrue : Qfalse;
+}
 
-	return val;
+
+/*
+ * Open a new database transaction.  If a transaction is already
+ * open, this is a no-op.
+ *
+ * +rwflag+ must be either MDBX_TXN_RDONLY or MDBX_TXN_READWRITE.
+ */
+void
+rmdbx_open_txn( rmdbx_db_t *db, int rwflag )
+{
+	if ( db->txn ) return;
+
+	int rc = mdbx_txn_begin( db->env, NULL, rwflag, &db->txn );
+	if ( rc != MDBX_SUCCESS ) {
+		rmdbx_close_all( db );
+		rb_raise( rmdbx_eDatabaseError, "mdbx_txn_begin: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+
+	if ( db->dbi == 0 ) {
+		rc = mdbx_dbi_open( db->txn, db->subdb, db->settings.db_flags, &db->dbi );
+		if ( rc != MDBX_SUCCESS ) {
+			rmdbx_close_all( db );
+			rb_raise( rmdbx_eDatabaseError, "mdbx_dbi_open: (%d) %s", rc, mdbx_strerror(rc) );
+		}
+	}
+
+	return;
+}
+
+
+/*
+ * Close any existing database transaction. If there is no
+ * active transaction, this is a no-op.  If there is a long
+ * running transaction open, this is a no-op.
+ *
+ * +txnflag must either be RMDBX_TXN_ROLLBACK or RMDBX_TXN_COMMIT.
+ */
+void
+rmdbx_close_txn( rmdbx_db_t *db, int txnflag )
+{
+	if ( ! db->txn || db->state.retain_txn > -1 ) return;
+
+	if ( txnflag == RMDBX_TXN_COMMIT ) {
+		mdbx_txn_commit( db->txn );
+	}
+	else {
+		mdbx_txn_abort( db->txn );
+	}
+
+	db->txn = 0;
+	return;
+}
+
+
+/*
+ * call-seq:
+ *    db.open_transaction( mode )
+ *
+ * Open a new long-running transaction.  If +mode+ is true,
+ * it is opened read/write.
+ *
+ */
+VALUE
+rmdbx_rb_opentxn( VALUE self, VALUE mode )
+{
+	UNWRAP_DB( self, db );
+	CHECK_HANDLE();
+
+	rmdbx_open_txn( db, RTEST(mode) ? MDBX_TXN_READWRITE : MDBX_TXN_RDONLY );
+	db->state.retain_txn = RTEST(mode) ? 1 : 0;
+
+	return Qtrue;
+}
+
+
+/*
+ * call-seq:
+ *    db.close_transaction( mode )
+ *
+ * Close a long-running transaction.  If +write+ is true,
+ * the transaction is committed.  Otherwise, rolled back.
+ *
+ */
+VALUE
+rmdbx_rb_closetxn( VALUE self, VALUE write )
+{
+	UNWRAP_DB( self, db );
+
+	db->state.retain_txn = -1;
+	rmdbx_close_txn( db, RTEST(write) ? RMDBX_TXN_COMMIT : RMDBX_TXN_ROLLBACK );
+
+	return Qtrue;
+}
+
+
+/*
+ * Open a cursor for iteration.
+ */
+void
+rmdbx_open_cursor( rmdbx_db_t *db )
+{
+	CHECK_HANDLE();
+	if ( ! db->txn ) rb_raise( rmdbx_eDatabaseError, "No snapshot or transaction currently open." );
+
+	int rc = mdbx_cursor_open( db->txn, db->dbi, &db->cursor );
+	if ( rc != MDBX_SUCCESS ) {
+		rmdbx_close_all( db );
+		rb_raise( rmdbx_eDatabaseError, "Unable to open cursor: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+
+	return;
 }
 
 
@@ -423,7 +612,7 @@ rmdbx_each_key( VALUE self )
 	UNWRAP_DB( self, db );
 	int state;
 
-	CHECK_HANDLE;
+	CHECK_HANDLE();
 	rmdbx_open_cursor( db );
 	RETURN_ENUMERATOR( self, 0, 0 );
 
@@ -472,7 +661,7 @@ rmdbx_each_value( VALUE self )
 	UNWRAP_DB( self, db );
 	int state;
 
-	CHECK_HANDLE;
+	CHECK_HANDLE();
 	rmdbx_open_cursor( db );
 	RETURN_ENUMERATOR( self, 0, 0 );
 
@@ -523,7 +712,7 @@ rmdbx_each_pair( VALUE self )
 	UNWRAP_DB( self, db );
 	int state;
 
-	CHECK_HANDLE;
+	CHECK_HANDLE();
 	rmdbx_open_cursor( db );
 	RETURN_ENUMERATOR( self, 0, 0 );
 
@@ -538,201 +727,6 @@ rmdbx_each_pair( VALUE self )
 }
 
 
-
-/* call-seq:
- *    db.length -> Integer
- *
- * Returns the count of keys in the currently selected collection.
- */
-VALUE
-rmdbx_length( VALUE self )
-{
-	UNWRAP_DB( self, db );
-	MDBX_stat mstat;
-
-	CHECK_HANDLE;
-	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
-
-	int rc = mdbx_dbi_stat( db->txn, db->dbi, &mstat, sizeof(mstat) );
-	if ( rc != MDBX_SUCCESS )
-		rb_raise( rmdbx_eDatabaseError, "mdbx_dbi_stat: (%d) %s", rc, mdbx_strerror(rc) );
-
-	VALUE rv = LONG2FIX( mstat.ms_entries );
-	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
-
-	return rv;
-}
-
-
-/* call-seq:
- *    db.include?( 'key' ) => bool
- *
- * Returns true if the current collection contains +key+.
- */
-VALUE
-rmdbx_include( VALUE self, VALUE key )
-{
-	int rc;
-	UNWRAP_DB( self, db );
-
-	CHECK_HANDLE;
-	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
-
-	MDBX_val ckey = rmdbx_key_for( key );
-	MDBX_val data;
-	rc = mdbx_get( db->txn, db->dbi, &ckey, &data );
-	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
-
-	switch ( rc ) {
-		case MDBX_SUCCESS:
-			return Qtrue;
-
-		case MDBX_NOTFOUND:
-			return Qfalse;
-
-		default:
-			rmdbx_close( self );
-			rb_raise( rmdbx_eDatabaseError, "Unable to fetch key: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-}
-
-
-/* call-seq:
- *    db[ 'key' ] => value
- *
- * Return a single value for +key+ immediately.
- */
-VALUE
-rmdbx_get_val( VALUE self, VALUE key )
-{
-	int rc;
-	UNWRAP_DB( self, db );
-
-	CHECK_HANDLE;
-	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
-
-	MDBX_val ckey = rmdbx_key_for( key );
-	MDBX_val data;
-	VALUE rv;
-	rc = mdbx_get( db->txn, db->dbi, &ckey, &data );
-	rmdbx_close_txn( db, RMDBX_TXN_ROLLBACK );
-
-	switch ( rc ) {
-		case MDBX_SUCCESS:
-			rv = rb_str_new( data.iov_base, data.iov_len );
-			return rmdbx_deserialize( self, rv );
-
-		case MDBX_NOTFOUND:
-			return Qnil;
-
-		default:
-			rmdbx_close( self );
-			rb_raise( rmdbx_eDatabaseError, "Unable to fetch value: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-}
-
-
-/* call-seq:
- *    db[ 'key' ] = value
- *
- * Set a single value for +key+.  If the value is +nil+, the
- * key is removed.
- */
-VALUE
-rmdbx_put_val( VALUE self, VALUE key, VALUE val )
-{
-	int rc;
-	UNWRAP_DB( self, db );
-
-	CHECK_HANDLE;
-	rmdbx_open_txn( db, MDBX_TXN_READWRITE );
-
-	MDBX_val ckey = rmdbx_key_for( key );
-
-	// FIXME: DUPSORT is enabled -- different api?
-	// See:  MDBX_NODUPDATA / MDBX_NOOVERWRITE
-	if ( NIL_P(val) ) { /* remove if set to nil */
-		rc = mdbx_del( db->txn, db->dbi, &ckey, NULL );
-	}
-	else {
-		MDBX_val old;
-		MDBX_val data = rmdbx_val_for( self, val );
-		rc = mdbx_replace( db->txn, db->dbi, &ckey, &data, &old, 0 );
-	}
-
-	rmdbx_close_txn( db, RMDBX_TXN_COMMIT );
-
-	switch ( rc ) {
-		case MDBX_SUCCESS:
-			return val;
-		case MDBX_NOTFOUND:
-			return Qnil;
-		default:
-			rb_raise( rmdbx_eDatabaseError, "Unable to store value: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-}
-
-
-/*
- * call-seq:
- *    db.statistics => (hash of stats)
- *
- * Returns a hash populated with various metadata for the opened
- * database.
- *
- */
-VALUE
-rmdbx_stats( VALUE self )
-{
-	UNWRAP_DB( self, db );
-	CHECK_HANDLE;
-
-	return rmdbx_gather_stats( db );
-}
-
-
-/*
- * Return the currently selected collection, or +nil+ if at the
- * top-level.
- */
-VALUE
-rmdbx_get_subdb( VALUE self )
-{
-	UNWRAP_DB( self, db );
-	return ( db->subdb == NULL ) ? Qnil : rb_str_new_cstr( db->subdb );
-}
-
-
-/*
- * Sets the current collection name for read/write operations.
- *
- */
-VALUE
-rmdbx_set_subdb( VALUE self, VALUE name )
-{
-	UNWRAP_DB( self, db );
-
-	/* Provide a friendlier error message if max_collections is 0. */
-	if ( db->settings.max_collections == 0 )
-		rb_raise( rmdbx_eDatabaseError, "Unable to change collection: collections are not enabled." );
-
-	/* All transactions must be closed when switching database handles. */
-	if ( db->txn )
-		rb_raise( rmdbx_eDatabaseError, "Unable to change collection: transaction open" );
-
-	db->subdb = NIL_P( name ) ? NULL : StringValueCStr( name );
-
-	/* Reset the db handle and issue a single transaction to reify
-	   the collection.
-	*/
-	rmdbx_close_dbi( db );
-	rmdbx_open_txn( db, MDBX_TXN_READWRITE );
-	rmdbx_close_txn( db, RMDBX_TXN_COMMIT );
-
-	return self;
-}
-
-
 /*
  * Open an existing (or create a new) mdbx database at filesystem
  * +path+.  In block form, the database is automatically closed.
@@ -772,57 +766,88 @@ rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 	db->state.open       = 0;
 	db->state.retain_txn = -1;
 	db->settings.env_flags       = MDBX_ENV_DEFAULTS;
+	db->settings.db_flags        = MDBX_DB_DEFAULTS | MDBX_CREATE;
 	db->settings.mode            = 0644;
 	db->settings.max_collections = 0;
 	db->settings.max_readers     = 0;
 	db->settings.max_size        = 0;
 
-	/* Options setup, overrides.
-	 */
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("mode") ) );
-	if ( ! NIL_P(opt) ) db->settings.mode = FIX2INT( opt );
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("max_collections") ) );
-	if ( ! NIL_P(opt) ) db->settings.max_collections = FIX2INT( opt );
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("max_readers") ) );
-	if ( ! NIL_P(opt) ) db->settings.max_readers = FIX2INT( opt );
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("max_size") ) );
-	if ( ! NIL_P(opt) ) db->settings.max_size = NUM2LONG( opt );
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("nosubdir") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOSUBDIR;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("readonly") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_RDONLY;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("exclusive") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_EXCLUSIVE;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("compat") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_ACCEDE;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("writemap") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_WRITEMAP;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("no_threadlocal") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOTLS;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("no_readahead") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NORDAHEAD;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("no_memory_init") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOMEMINIT;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("coalesce") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_COALESCE;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("lifo_reclaim") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_LIFORECLAIM;
-	opt = rb_hash_aref( opts, ID2SYM( rb_intern("no_metasync") ) );
-	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOMETASYNC;
-
-	/* Duplicate keys, on mdbx_dbi_open, maybe set here? */
-	/* MDBX_DUPSORT = UINT32_C(0x04), */
-
 	/* Set instance variables.
 	 */
 	rb_iv_set( self, "@path", path );
-	rb_iv_set( self, "@options", opts );
+	rb_iv_set( self, "@options", rb_hash_dup( opts ) );
+
+	/* Environment and database options setup, overrides.
+	 */
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("coalesce") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_COALESCE;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("compatible") ) );
+	if ( RTEST(opt) ) {
+		db->settings.db_flags  = db->settings.db_flags | MDBX_DB_ACCEDE;
+		db->settings.env_flags = db->settings.env_flags | MDBX_ACCEDE;
+	}
+	/* opt = rb_hash_delete( opts, ID2SYM( rb_intern("duplicate_keys") ) ); */
+	/* if ( RTEST(opt) ) db->settings.db_flags = db->settings.db_flags | MDBX_DUPSORT; */
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("exclusive") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_EXCLUSIVE;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("lifo_reclaim") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_LIFORECLAIM;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("max_collections") ) );
+	if ( ! NIL_P(opt) ) db->settings.max_collections = FIX2INT( opt );
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("max_readers") ) );
+	if ( ! NIL_P(opt) ) db->settings.max_readers = FIX2INT( opt );
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("max_size") ) );
+	if ( ! NIL_P(opt) ) db->settings.max_size = NUM2LONG( opt );
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("mode") ) );
+	if ( ! NIL_P(opt) ) db->settings.mode = FIX2INT( opt );
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("no_memory_init") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOMEMINIT;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("no_metasync") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOMETASYNC;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("no_subdir") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOSUBDIR;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("no_readahead") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NORDAHEAD;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("no_threadlocal") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_NOTLS;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("readonly") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_RDONLY;
+	opt = rb_hash_delete( opts, ID2SYM( rb_intern("writemap") ) );
+	if ( RTEST(opt) ) db->settings.env_flags = db->settings.env_flags | MDBX_WRITEMAP;
+
+	/* Bail early on incompatible options. FIXME: I don't think this is true. */
+	/* if ( db->settings.max_collections > 0 && */
+	/* 		rmdbx_flag_enabled( db->settings.db_flags, MDBX_DUPSORT ) ) { */
+	/* 	rb_raise( rb_eArgError, "Collections and multiple values per key are mutually exclusive options." ); */
+	/* } */
+
+	if ( rb_hash_size_num(opts) > 0 ) {
+		rb_raise( rb_eArgError, "Unknown option(s): %"PRIsVALUE, opts );
+	}
 
 	rmdbx_open_env( self );
 	return self;
 }
 
 
+/*
+ * call-seq:
+ *    db.statistics => (hash of stats)
+ *
+ * Returns a hash populated with various metadata for the opened
+ * database.
+ *
+ */
+VALUE
+rmdbx_stats( VALUE self )
+{
+	UNWRAP_DB( self, db );
+	CHECK_HANDLE();
+
+	return rmdbx_gather_stats( db );
+}
+
+
 /*
  * call-seq:
  *    db.clone => [copy of db]
@@ -872,17 +897,19 @@ rmdbx_init_database()
 	rb_define_method( rmdbx_cDatabase, "close", rmdbx_close, 0 );
 	rb_define_method( rmdbx_cDatabase, "closed?", rmdbx_closed_p, 0 );
 	rb_define_method( rmdbx_cDatabase, "drop", rmdbx_drop, 1 );
-	rb_define_method( rmdbx_cDatabase, "each_key", rmdbx_each_key, 0 );
-	rb_define_method( rmdbx_cDatabase, "each_pair", rmdbx_each_pair, 0 );
-	rb_define_method( rmdbx_cDatabase, "each_value", rmdbx_each_value, 0 );
-	rb_define_method( rmdbx_cDatabase, "in_transaction?", rmdbx_in_transaction_p, 0 );
 	rb_define_method( rmdbx_cDatabase, "include?", rmdbx_include, 1 );
 	rb_define_method( rmdbx_cDatabase, "length", rmdbx_length, 0 );
 	rb_define_method( rmdbx_cDatabase, "reopen", rmdbx_open_env, 0 );
 	rb_define_method( rmdbx_cDatabase, "[]", rmdbx_get_val, 1 );
 	rb_define_method( rmdbx_cDatabase, "[]=", rmdbx_put_val, 2 );
 
+	/* Enumerables */
+	rb_define_method( rmdbx_cDatabase, "each_key", rmdbx_each_key, 0 );
+	rb_define_method( rmdbx_cDatabase, "each_pair", rmdbx_each_pair, 0 );
+	rb_define_method( rmdbx_cDatabase, "each_value", rmdbx_each_value, 0 );
+
 	/* Manually open/close transactions from ruby. */
+	rb_define_method( rmdbx_cDatabase, "in_transaction?", rmdbx_in_transaction_p, 0 );
 	rb_define_protected_method( rmdbx_cDatabase, "open_transaction",  rmdbx_rb_opentxn, 1 );
 	rb_define_protected_method( rmdbx_cDatabase, "close_transaction", rmdbx_rb_closetxn, 1 );
 
@@ -895,3 +922,4 @@ rmdbx_init_database()
 	rb_require( "mdbx/database" );
 }
 
+
diff --git a/ext/mdbx_ext/mdbx_ext.h b/ext/mdbx_ext/mdbx_ext.h
index a3f45bb..64bb63d 100644
--- a/ext/mdbx_ext/mdbx_ext.h
+++ b/ext/mdbx_ext/mdbx_ext.h
@@ -4,12 +4,23 @@
 
 #include "mdbx.h"
 
-#ifndef MDBX_EXT_0_9_3
-#define MDBX_EXT_0_9_3
+#ifndef RBMDBX_EXT
+#define RBMDBX_EXT
 
 #define RMDBX_TXN_ROLLBACK 0
 #define RMDBX_TXN_COMMIT 1
 
+/* Shortcut for fetching wrapped data structure.
+ */
+#define UNWRAP_DB( self, db ) \
+	rmdbx_db_t *db; \
+	TypedData_Get_Struct( self, rmdbx_db_t, &rmdbx_db_data, db )
+
+/* Raise if current DB is not open. */
+#define CHECK_HANDLE() \
+	if ( ! db->state.open ) rb_raise( rmdbx_eDatabaseError, "Closed database." )
+
+
 /*
  * A struct encapsulating an instance's DB
  * state and settings.
@@ -21,7 +32,8 @@ struct rmdbx_db {
 	MDBX_cursor *cursor;
 
     struct {
-       int env_flags;
+       unsigned int env_flags;
+       unsigned int db_flags;
        int mode;
        int open;
        int max_collections;
@@ -40,12 +52,11 @@ struct rmdbx_db {
 typedef struct rmdbx_db rmdbx_db_t;
 
 static const rb_data_type_t rmdbx_db_data;
-extern void rmdbx_free( void *db ); /* forward declaration for the allocator */
+
 
 /* ------------------------------------------------------------
  * Globals
  * ------------------------------------------------------------ */
-
 extern VALUE rmdbx_mMDBX;
 extern VALUE rmdbx_cDatabase;
 extern VALUE rmdbx_eDatabaseError;
@@ -55,13 +66,15 @@ extern VALUE rmdbx_eRollback;
 /* ------------------------------------------------------------
  * Functions
  * ------------------------------------------------------------ */
+extern void rmdbx_free( void *db ); /* forward declaration for the allocator */
 extern void Init_rmdbx ( void );
 extern void rmdbx_init_database ( void );
+extern void rmdbx_close_all( rmdbx_db_t* );
 extern void rmdbx_open_txn( rmdbx_db_t*, int );
 extern void rmdbx_close_txn( rmdbx_db_t*, int );
-
+extern void rmdbx_open_cursor( rmdbx_db_t* );
 extern VALUE rmdbx_gather_stats( rmdbx_db_t* );
 
 
-#endif /* define MDBX_EXT_0_9_3 */
+#endif /* define RBMDBX_EXT */
 
diff --git a/ext/mdbx_ext/stats.c b/ext/mdbx_ext/stats.c
index 7ac003d..c645a80 100644
--- a/ext/mdbx_ext/stats.c
+++ b/ext/mdbx_ext/stats.c
@@ -3,8 +3,6 @@
  * Expose a bunch of mdbx internals to ruby.
  * This is all largely stolen from mdbx_stat.c.
  *
- * Entry point is rmdbx_stats() in database.c.
- *
  */
 
 #include "mdbx_ext.h"
@@ -28,6 +26,32 @@ rmdbx_gather_build_stats( VALUE stat )
 }
 
 
+/*
+ * Grab current memory usage.  (Available since MDBX 0.10.0).
+ */
+void
+rmdbx_gather_memory_stats( VALUE stat )
+{
+	if (! ( MDBX_VERSION_MAJOR >= 0 && MDBX_VERSION_MINOR >= 10 ) )
+		return;
+
+	VALUE mem = rb_hash_new();
+	rb_hash_aset( stat, ID2SYM(rb_intern("system_memory")), mem );
+
+	intptr_t page_size;
+	intptr_t total_pages;
+	intptr_t avail_pages;
+
+	mdbx_get_sysraminfo( &page_size, &total_pages, &avail_pages );
+
+	rb_hash_aset( mem, ID2SYM(rb_intern("pagesize")),    LONG2FIX( page_size ) );
+	rb_hash_aset( mem, ID2SYM(rb_intern("total_pages")), LONG2FIX( total_pages ) );
+	rb_hash_aset( mem, ID2SYM(rb_intern("avail_pages")), LONG2FIX( avail_pages ) );
+
+	return;
+}
+
+
 /*
  * Metadata for the database file.
  */
@@ -80,6 +104,16 @@ rmdbx_gather_environment_stats(
 
 	rb_hash_aset( environ, ID2SYM(rb_intern("pagesize")),
 			INT2NUM(mstat.ms_psize) );
+	rb_hash_aset( environ, ID2SYM(rb_intern("branch_pages")),
+			LONG2NUM(mstat.ms_branch_pages) );
+	rb_hash_aset( environ, ID2SYM(rb_intern("leaf_pages")),
+			LONG2NUM(mstat.ms_leaf_pages) );
+	rb_hash_aset( environ, ID2SYM(rb_intern("overflow_pages")),
+			LONG2NUM(mstat.ms_overflow_pages) );
+	rb_hash_aset( environ, ID2SYM(rb_intern("btree_depth")),
+			INT2NUM(mstat.ms_depth) );
+	rb_hash_aset( environ, ID2SYM(rb_intern("entries")),
+			LONG2NUM(mstat.ms_entries) );
 	rb_hash_aset( environ, ID2SYM(rb_intern("last_txnid")),
 			INT2NUM(menvinfo.mi_recent_txnid) );
 	rb_hash_aset( environ, ID2SYM(rb_intern("last_reader_txnid")),
@@ -101,7 +135,7 @@ rmdbx_gather_environment_stats(
  *
  */
 int
-reader_list_callback(
+rmdbx_reader_list_cb(
 	void *ctx,
 	int num,
 	int slot,
@@ -148,7 +182,7 @@ rmdbx_gather_reader_stats(
 {
 	VALUE readers = rb_ary_new();
 
-	mdbx_reader_list( db->env, reader_list_callback, (void*)readers );
+	mdbx_reader_list( db->env, rmdbx_reader_list_cb, (void*)readers );
 	rb_hash_aset( stat, ID2SYM(rb_intern("readers")), readers );
 
 	return;
@@ -168,6 +202,7 @@ rmdbx_gather_stats( rmdbx_db_t *db )
 	MDBX_stat mstat;
 	MDBX_envinfo menvinfo;
 
+	rmdbx_gather_memory_stats( stat );
 	rmdbx_gather_build_stats( stat );
 
 	rmdbx_open_txn( db, MDBX_TXN_RDONLY );
@@ -183,9 +218,6 @@ rmdbx_gather_stats( rmdbx_db_t *db )
 	rmdbx_gather_environment_stats( stat, mstat, menvinfo );
 	rmdbx_gather_reader_stats( db, stat, mstat, menvinfo );
 
-	/* TODO: database and subdatabase stats */
-
 	return stat;
 }
 
-
diff --git a/lib/mdbx/database.rb b/lib/mdbx/database.rb
index 1cd1293..a25114f 100644
--- a/lib/mdbx/database.rb
+++ b/lib/mdbx/database.rb
@@ -29,10 +29,23 @@ class MDBX::Database
 	### Unless otherwise mentioned, option keys are symbols, and values
 	### are boolean.
 	###
-	### [:mode]
-	###   Whe creating a new database, set permissions to this 4 digit
-	###   octal number.  Defaults to `0644`.  Set to `0` to never automatically
-	###   create a new file, only opening existing databases.
+	### [:coalesce]
+	###   Attempt to coalesce items for the garbage collector,
+	###   potentialy increasing the chance of unallocating storage
+	###   earlier.
+	###
+	### [:compatible]
+	###   Skip compatibility checks when opening an in-use database with
+	###   unknown or mismatched flag values.
+	###
+	### [:exclusive]
+	###   Access is restricted to the first opening process. Other attempts
+	###   to use this database (even in readonly mode) are denied.
+	###
+	### [:lifo_reclaim]
+	###   Recycle garbage collected items via LIFO, instead of FIFO.
+	###   Depending on underlying hardware (disk write-back cache), this
+	###   could increase write performance.
 	###
 	### [:max_collections]
 	###   Set the maximum number of "subdatabase" collections allowed. By
@@ -45,51 +58,38 @@ class MDBX::Database
 	###   Set an upper boundary (in bytes) for the database map size.
 	###   The default is 10485760 bytes.
 	###
-	### [:nosubdir]
+	### [:mode]
+	###   Whe creating a new database, set permissions to this 4 digit
+	###   octal number.  Defaults to `0644`.  Set to `0` to never automatically
+	###   create a new file, only opening existing databases.
+	###
+	### [:no_memory_init]
+	###   Skip initializing malloc'ed memory to zeroes before writing.
+	###
+	### [:no_metasync]
+	###   A system crash may sacrifice the last commit for a potentially
+	###   large write performance increase.  Database integrity is
+	###   maintained.
+	###
+	### [:no_subdir]
 	###   When creating a new database, don't put the data and lock file
 	###   under a dedicated subdirectory.
 	###
-	### [:readonly]
-	###   Reject any write attempts while using this database handle.
-	###
-	### [:exclusive]
-	###   Access is restricted to the first opening process. Other attempts
-	###   to use this database (even in readonly mode) are denied.
-	###
-	### [:compat]
-	###   Skip compatibility checks when opening an in-use database with
-	###   unknown or mismatched flag values.
-	###
-	### [:writemap]
-	###   Trade safety for speed for databases that fit within available
-	###   memory. (See MDBX documentation for details.)
-	###
-	### [:no_threadlocal]
-	###   Parallelize read-only transactions across threads.  Writes are
-	###   always thread local. (See MDBX documentatoin for details.)
-	###
 	### [:no_readahead]
 	###   Disable all use of OS readahead.  Potentially useful for
 	###   random reads wunder low memory conditions.  Default behavior
 	###   is to dynamically choose when to use or omit readahead.
 	###
-	### [:no_memory_init]
-	###   Skip initializing malloc'ed memory to zeroes before writing.
+	### [:no_threadlocal]
+	###   Parallelize read-only transactions across threads.  Writes are
+	###   always thread local. (See MDBX documentatoin for details.)
 	###
-	### [:coalesce]
-	###   Attempt to coalesce items for the garbage collector,
-	###   potentialy increasing the chance of unallocating storage
-	###   earlier.
+	### [:readonly]
+	###   Reject any write attempts while using this database handle.
 	###
-	### [:lifo_reclaim]
-	###   Recycle garbage collected items via LIFO, instead of FIFO.
-	###   Depending on underlying hardware (disk write-back cache), this
-	###   could increase write performance.
-	###
-	### [:no_metasync]
-	###   A system crash may sacrifice the last commit for a potentially
-	###   large write performance increase.  Database integrity is
-	###   maintained.
+	### [:writemap]
+	###   Trade safety for speed for databases that fit within available
+	###   memory. (See MDBX documentation for details.)
 	###
 	def self::open( *args, &block )
 		db = new( *args )
diff --git a/spec/mdbx/database_spec.rb b/spec/mdbx/database_spec.rb
index 7b44d33..d82ce20 100644
--- a/spec/mdbx/database_spec.rb
+++ b/spec/mdbx/database_spec.rb
@@ -3,20 +3,18 @@
 
 require_relative '../lib/helper'
 
-
 RSpec.describe( MDBX::Database ) do
 
-	before( :all ) do
-		db = described_class.open( TEST_DATABASE.to_s )
-		db.clear
-		db.close
-	end
-
 	it "disallows direct calls to #new" do
 		expect{ described_class.new }.
 			to raise_exception( NoMethodError, /private/ )
 	end
 
+	it "raises an exception if passed unknown options" do
+		expect{ described_class.open( TEST_DATABASE.to_s, nope: true ) }.
+			to raise_exception( ArgumentError, /unknown option/i )
+	end
+
 	it "knows the env handle open/close state" do
 		db = described_class.open( TEST_DATABASE.to_s )
 		expect( db.closed? ).to be_falsey
@@ -52,12 +50,9 @@ RSpec.describe( MDBX::Database ) do
 
 		let!( :db ) { described_class.open( TEST_DATABASE.to_s ) }
 
-		before( :each ) do
-			db.clear
-		end
-
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 		it "can be reopened" do
@@ -86,12 +81,9 @@ RSpec.describe( MDBX::Database ) do
 
 		let!( :db ) { described_class.open( TEST_DATABASE.to_s ) }
 
-		before( :each ) do
-			db.clear
-		end
-
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 
@@ -181,16 +173,23 @@ RSpec.describe( MDBX::Database ) do
 	end
 
 
+	# context 'duplicate keys' do
+    #
+	# 	let( :db ) { described_class.open( TEST_DATABASE.to_s, max_collections: 5, duplicate_keys: true ) }
+    #
+	# 	after( :each ) do
+	# 		db.close
+	# 	end
+	# end
+
+
 	context 'collections' do
 
 		let!( :db ) { described_class.open( TEST_DATABASE.to_s, max_collections: 5 ) }
 
-		before( :each ) do
-			db.clear
-		end
-
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 		it "fail if the max_collections option is not specified when opening" do
@@ -324,6 +323,17 @@ RSpec.describe( MDBX::Database ) do
 			expect( db['doom'] ).to be_nil
 		end
 
+		it "retains other collections, only dropping what is specified" do
+			db.collection( 'boots' )
+			db.collection( 'pants' )
+			db.main
+			db.drop( 'boots' )
+
+			expect( db.collection ).to be_nil
+			expect( db['doom'] ).to be_nil
+			expect( db ).to have_key( :pants )
+		end
+
 		it "retains the collection environment when clearing data" do
 			db.collection( 'doom' )
 			db[ 'key' ] = 1
@@ -340,7 +350,7 @@ RSpec.describe( MDBX::Database ) do
 
 	context 'transactions' do
 
-		let!( :db ) { described_class.open( TEST_DATABASE.to_s, max_collections: 5 ) }
+		let( :db ) { described_class.open( TEST_DATABASE.to_s, max_collections: 5 ) }
 
 		before( :each ) do
 			db.clear
@@ -348,6 +358,7 @@ RSpec.describe( MDBX::Database ) do
 
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 		it "knows when a transaction is currently open" do
@@ -447,7 +458,7 @@ RSpec.describe( MDBX::Database ) do
 
 	context "iterators" do
 
-		let( :db ) {
+		let!( :db ) {
 			described_class.open( TEST_DATABASE.to_s, max_collections: 5 ).collection( 'iter' )
 		}
 
@@ -457,6 +468,7 @@ RSpec.describe( MDBX::Database ) do
 
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 		it "raises an exception if the caller didn't open a transaction first" do
@@ -496,12 +508,13 @@ RSpec.describe( MDBX::Database ) do
 
 	context "serialization" do
 
-		let( :db ) {
+		let!( :db ) {
 			described_class.open( TEST_DATABASE.to_s )
 		}
 
 		after( :each ) do
 			db.close
+			TEST_DATABASE.rmtree
 		end
 
 		it "uses Marshalling as default" do