diff --git a/ext/mdbx_ext/database.c b/ext/mdbx_ext/database.c
index 23d9486..fd9c367 100644
--- a/ext/mdbx_ext/database.c
+++ b/ext/mdbx_ext/database.c
@@ -25,7 +25,10 @@ struct rmdbx_db {
 	MDBX_txn *txn;
 	MDBX_cursor *cursor;
 	int env_flags;
+	int mode;
 	int open;
+	int max_collections;
+	char *path;
 	char *subdb;
 };
 typedef struct rmdbx_db rmdbx_db_t;
@@ -93,11 +96,41 @@ rmdbx_close( VALUE self )
 }
 
 
+/*
+ * Open the DB environment handle.
+ */
+VALUE
+rmdbx_open_env( VALUE self )
+{
+	int rc;
+	UNWRAP_DB( self, db );
+	rmdbx_close_all( db );
+
+	/* Allocate an mdbx environment.
+	 */
+	rc = mdbx_env_create( &db->env );
+	if ( rc != MDBX_SUCCESS )
+		rb_raise( rmdbx_eDatabaseError, "mdbx_env_create: (%d) %s", rc, mdbx_strerror(rc) );
+
+	/* Set the maximum number of named databases for the environment. */
+	mdbx_env_set_maxdbs( db->env, db->max_collections );
+
+	rc = mdbx_env_open( db->env, db->path, db->env_flags, db->mode );
+	if ( rc != MDBX_SUCCESS ) {
+		rmdbx_close( self );
+		rb_raise( rmdbx_eDatabaseError, "mdbx_env_open: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+	db->open = 1;
+
+	return Qtrue;
+}
+
+
 /*
  * call-seq:
  *    db.closed? #=> false
  *
- * Predicate: return true if the database handle is closed.
+ * Predicate: return true if the database environment is closed.
  */
 VALUE
 rmdbx_closed_p( VALUE self )
@@ -139,23 +172,31 @@ rmdbx_open_txn( VALUE self, int rwflag )
 
 /*
  * call-seq:
- *    db.destroy
+ *    db.clear
  *
- * Empty the database (or subdatabase) on disk.  Unrecoverable.
+ * Empty the database (or collection) on disk.  Unrecoverable!
  */
 VALUE
-rmdbx_destroy( VALUE self )
+rmdbx_clear( VALUE self )
 {
 	UNWRAP_DB( self, db );
+
 	rmdbx_open_txn( self, MDBX_TXN_READWRITE );
 	int rc = mdbx_drop( db->txn, db->dbi, true );
 
-	// FIXME: something fishy here
-	//
 	if ( rc != 0 )
 		rb_raise( rmdbx_eDatabaseError, "mdbx_drop: (%d) %s", rc, mdbx_strerror(rc) );
+
 	mdbx_txn_commit( db->txn );
-	db->open = 0;
+
+	// Close the current handle, will be re-opened
+	// on the next txn.
+	//
+	if ( db->dbi ) {
+		mdbx_dbi_close( db->env, db->dbi );
+		db->dbi = 0;
+	}
+
 	return Qnil;
 }
 
@@ -199,6 +240,42 @@ rmdbx_val_for( VALUE self, VALUE arg )
 }
 
 
+/* call-seq:
+ *    db.keys #=> [ 'key1', 'key2', ... ]
+ *
+ * Return an array of all keys in the current collection.
+ */
+VALUE
+rmdbx_keys( VALUE self )
+{
+	UNWRAP_DB( self, db );
+	VALUE rv = rb_ary_new();
+	MDBX_val key, data;
+	int rc;
+
+	if ( ! db->open ) rb_raise( rmdbx_eDatabaseError, "Closed database." );
+
+	rmdbx_open_txn( self, MDBX_TXN_RDONLY );
+	rc = mdbx_cursor_open( db->txn, db->dbi, &db->cursor);
+
+	if ( rc != MDBX_SUCCESS ) {
+		rmdbx_close( self );
+		rb_raise( rmdbx_eDatabaseError, "Unable to open cursor: (%d) %s", rc, mdbx_strerror(rc) );
+	}
+
+	mdbx_cursor_get( db->cursor, &key, &data, MDBX_FIRST );
+	rb_ary_push( rv, rb_str_new( key.iov_base, key.iov_len ) );
+	while ( mdbx_cursor_get( db->cursor, &key, &data, MDBX_NEXT ) == 0 ) {
+		rb_ary_push( rv, rb_str_new( key.iov_base, key.iov_len ) );
+	}
+
+	mdbx_cursor_close( db->cursor );
+	db->cursor = NULL;
+	mdbx_txn_abort( db->txn );
+	return rv;
+}
+
+
 /* call-seq:
  *    db[ 'key' ]  #=> value
  *
@@ -211,7 +288,7 @@ rmdbx_get_val( VALUE self, VALUE key )
 	VALUE deserialize_proc;
 	UNWRAP_DB( self, db );
 
-	if ( RTEST(rmdbx_closed_p(self)) ) rb_raise( rmdbx_eDatabaseError, "Closed database." );
+	if ( ! db->open ) rb_raise( rmdbx_eDatabaseError, "Closed database." );
 
 	rmdbx_open_txn( self, MDBX_TXN_RDONLY );
 
@@ -224,10 +301,10 @@ rmdbx_get_val( VALUE self, VALUE key )
 		case MDBX_SUCCESS:
 			deserialize_proc = rb_iv_get( self, "@deserializer" );
 			if ( ! NIL_P( deserialize_proc ) ) {
-				return rb_funcall( deserialize_proc, rb_intern("call"), 1, rb_str_new2(data.iov_base) );
+				return rb_funcall( deserialize_proc, rb_intern("call"), 1, rb_str_new_cstr(data.iov_base) );
 			}
 			else {
-				return rb_str_new2( data.iov_base );
+				return rb_str_new_cstr( data.iov_base );
 			}
 
 		case MDBX_NOTFOUND:
@@ -251,7 +328,7 @@ rmdbx_put_val( VALUE self, VALUE key, VALUE val )
 	int rc;
 	UNWRAP_DB( self, db );
 
-	if ( RTEST(rmdbx_closed_p(self)) ) rb_raise( rmdbx_eDatabaseError, "Closed database." );
+	if ( ! db->open ) rb_raise( rmdbx_eDatabaseError, "Closed database." );
 
 	rmdbx_open_txn( self, MDBX_TXN_READWRITE );
 
@@ -273,6 +350,8 @@ rmdbx_put_val( VALUE self, VALUE key, VALUE val )
 	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) );
 	}
@@ -290,7 +369,6 @@ rmdbx_put_val( VALUE self, VALUE key, VALUE val )
  */
 VALUE
 rmdbx_set_subdb( int argc, VALUE *argv, VALUE self )
-/* rmdbx_set_subdb( VALUE self, VALUE subdb ) */
 {
 	UNWRAP_DB( self, db );
 	VALUE subdb;
@@ -298,17 +376,19 @@ rmdbx_set_subdb( int argc, VALUE *argv, VALUE self )
 	rb_scan_args( argc, argv, "01", &subdb );
 	if ( argc == 0 ) {
 		if ( db->subdb == NULL ) return Qnil;
-		return rb_str_new2( db->subdb );
+		return rb_str_new_cstr( db->subdb );
 	}
 
 	rb_iv_set( self, "@collection", subdb );
 	db->subdb = NIL_P( subdb ) ? NULL : StringValueCStr( subdb );
 
-	// Close any current dbi handle, to be re-opened with
-	// the new collection on next access.
-	//
-	// FIXME:  Immediate transaction write to auto-create new env
-	//
+	/* Close any currently open dbi handle, to be re-opened with
+	 * the new collection on next access.
+	 * 
+	  FIXME:  Immediate transaction write to auto-create new env?
+	  Fetching from here at the moment causes an error if you
+	  haven't written anything yet.
+	 */
 	if ( db->dbi ) {
 		mdbx_dbi_close( db->env, db->dbi );
 		db->dbi = 0;
@@ -333,9 +413,9 @@ rmdbx_set_subdb( int argc, VALUE *argv, VALUE self )
 VALUE
 rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 {
-	int rc       = 0;
-	int mode     = 0644;
-	int env_flags = MDBX_ENV_DEFAULTS;
+	int mode            = 0644;
+	int max_collections = 0;
+	int env_flags       = MDBX_ENV_DEFAULTS;
 	VALUE path, opts, opt;
 
 	rb_scan_args( argc, argv, "11", &path, &opts );
@@ -354,6 +434,8 @@ rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 	 */
 	opt = rb_hash_aref( opts, ID2SYM( rb_intern("mode") ) );
 	if ( ! NIL_P(opt) ) mode = FIX2INT( opt );
+	opt = rb_hash_aref( opts, ID2SYM( rb_intern("max_collections") ) );
+	if ( ! NIL_P(opt) ) max_collections = FIX2INT( opt );
 	opt = rb_hash_aref( opts, ID2SYM( rb_intern("nosubdir") ) );
 	if ( RTEST(opt) ) env_flags = env_flags | MDBX_NOSUBDIR;
 	opt = rb_hash_aref( opts, ID2SYM( rb_intern("readonly") ) );
@@ -380,7 +462,6 @@ rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 	/* Duplicate keys, on mdbx_dbi_open, maybe set here? */
 	/* MDBX_DUPSORT = UINT32_C(0x04), */
 
-
 	/* Initialize the DB vals.
 	 */
 	UNWRAP_DB( self, db );
@@ -389,32 +470,18 @@ rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 	db->txn       = NULL;
 	db->cursor    = NULL;
 	db->env_flags = env_flags;
+	db->mode      = mode;
+	db->max_collections = max_collections;
+	db->path      = StringValueCStr( path );
 	db->open      = 0;
 	db->subdb     = NULL;
 
-	/* Allocate an mdbx environment.
-	 */
-	rc = mdbx_env_create( &db->env );
-	if ( rc != MDBX_SUCCESS )
-		rb_raise( rmdbx_eDatabaseError, "mdbx_env_create: (%d) %s", rc, mdbx_strerror(rc) );
-
-//FIXME: configurable	mdbx_env_set_maxdbs( db->env, 20 );
-	mdbx_env_set_maxdbs( db->env, 20 );
-
-	/* Open the DB handle on disk.
-	 */
-	rc = mdbx_env_open( db->env, StringValueCStr(path), env_flags, mode );
-	if ( rc != MDBX_SUCCESS ) {
-		rmdbx_close( self );
-		rb_raise( rmdbx_eDatabaseError, "mdbx_env_open: (%d) %s", rc, mdbx_strerror(rc) );
-	}
-
 	/* Set instance variables.
 	 */
-	db->open = 1;
 	rb_iv_set( self, "@path", path );
 	rb_iv_set( self, "@options", opts );
 
+	rmdbx_open_env( self );
 	return self;
 }
 
@@ -432,8 +499,10 @@ rmdbx_init_database()
 	rb_define_protected_method( rmdbx_cDatabase, "initialize", rmdbx_database_initialize, -1 );
 	rb_define_method( rmdbx_cDatabase, "collection", rmdbx_set_subdb, -1 );
 	rb_define_method( rmdbx_cDatabase, "close", rmdbx_close, 0 );
+	rb_define_method( rmdbx_cDatabase, "open", rmdbx_open_env, 0 );
 	rb_define_method( rmdbx_cDatabase, "closed?", rmdbx_closed_p, 0 );
-	rb_define_method( rmdbx_cDatabase, "destroy", rmdbx_destroy, 0 );
+	rb_define_method( rmdbx_cDatabase, "clear", rmdbx_clear, 0 );
+	rb_define_method( rmdbx_cDatabase, "keys", rmdbx_keys, 0 );
 	rb_define_method( rmdbx_cDatabase, "[]", rmdbx_get_val, 1 );
 	rb_define_method( rmdbx_cDatabase, "[]=", rmdbx_put_val, 2 );
 
diff --git a/lib/mdbx/database.rb b/lib/mdbx/database.rb
index b0787d4..6c4f927 100644
--- a/lib/mdbx/database.rb
+++ b/lib/mdbx/database.rb
@@ -9,7 +9,6 @@ require 'mdbx' unless defined?( MDBX )
 #
 class MDBX::Database
 
-
 	### Open an existing (or create a new) mdbx database at filesystem
 	### +path+.  In block form, the database is automatically closed.
 	###
@@ -40,6 +39,7 @@ class MDBX::Database
 	# Only instantiate Database objects via #open.
 	private_class_method :new
 
+
 	# The options used to instantiate this database.
 	attr_reader :options
 
@@ -52,5 +52,17 @@ class MDBX::Database
 	# A Proc for automatically deserializing values.
 	attr_accessor :deserializer
 
+
+	# Allow for some common nomenclature.
+	alias_method :namespace, :collection
+	alias_method :reopen, :open
+
+
+	### Switch to the top-level collection.
+	###
+	def main
+		return self.collection( nil )
+	end
+
 end # class MDBX::Database
 
diff --git a/spec/data/testdb/mdbx.dat b/spec/data/testdb/mdbx.dat
deleted file mode 100644
index 94a178e..0000000
Binary files a/spec/data/testdb/mdbx.dat and /dev/null differ
diff --git a/spec/lib/helper.rb b/spec/lib/helper.rb
index dbca1f7..f5bfff2 100644
--- a/spec/lib/helper.rb
+++ b/spec/lib/helper.rb
@@ -14,7 +14,7 @@ require 'mdbx'
 
 
 module MDBX::Testing
-	TEST_DATABASE = Pathname( __FILE__ ).parent.parent + 'data' + 'testdb'
+	TEST_DATABASE = Pathname( __FILE__ ).parent.parent.parent + 'tmp' + 'testdb'
 end
 
 
diff --git a/spec/mdbx/database_spec.rb b/spec/mdbx/database_spec.rb
index 735b5d1..b6feab8 100644
--- a/spec/mdbx/database_spec.rb
+++ b/spec/mdbx/database_spec.rb
@@ -10,7 +10,7 @@ RSpec.describe( MDBX::Database ) do
 			to raise_exception( NoMethodError, /private/ )
 	end
 
-	it "knows the db handle open/close state" do
+	it "knows the env handle open/close state" do
 		db = described_class.open( TEST_DATABASE.to_s )
 		expect( db.closed? ).to be_falsey
 		db.close
@@ -33,29 +33,95 @@ RSpec.describe( MDBX::Database ) do
 			db.close
 		end
 
+		it "can be reopened" do
+			db.close
+			expect( db ).to be_closed
+			db.reopen
+			expect( db ).to_not be_closed
+		end
+
 		it "knows its own path" do
-			expect( db.path ).to match( %r|data/testdb$| )
+			expect( db.path ).to match( %r|tmp/testdb$| )
 		end
 
 		it "fails if opened again within the same process" do
 			# This is a function of libmdbx internals, just testing
-			# here for behaviorals.
+			# here for behavior.
 			expect {
 				described_class.open( TEST_DATABASE.to_s )
 			}.
 			to raise_exception( MDBX::DatabaseError, /environment is already used/ )
 		end
 
+		it "can remove a key by setting its value to nil" do
+			db[ 'test' ] = "hi"
+			expect( db['test'] ).to eq( 'hi' )
+
+			db[ 'test' ] = nil
+			expect( db['test'] ).to be_nil
+
+			expect { db[ 'test' ] = nil }.to_not raise_exception
+		end
+
+		it "can return an array of its keys" do
+			db[ 'key1' ] = true
+			db[ 'key2' ] = true
+			db[ 'key3' ] = true
+			expect( db.keys ).to include( 'key1', 'key2', 'key3' )
+		end
+	end
+
+
+	context 'collections' do
+
+		let!( :db ) { described_class.open( TEST_DATABASE.to_s, max_collections: 5 ) }
+
+		after( :each ) do
+			db.close
+		end
+
+		it "fail if the max_collections option is not specified when opening" do
+			db.close
+			db = described_class.open( TEST_DATABASE.to_s )
+			db.collection( 'bucket' )
+
+			expect{ db['key'] = true }.to raise_exception( /MDBX_DBS_FULL/ )
+		end
+
+		it "disallows regular key/val storage for namespace keys" do
+			db.collection( 'bucket' )
+			db[ 'okay' ] = 1
+			db.collection( nil )
+
+			expect{ db['bucket'] = 1  }.to raise_exception( /MDBX_INCOMPATIBLE/ )
+		end
+
 		it "defaults to the top-level namespace" do
 			expect( db.collection ).to be_nil
 		end
 
 		it "can set a collection namespace" do
+			expect( db.collection ).to be_nil
+			db[ 'key' ] = true
+
 			db.collection( 'bucket' )
 			expect( db.collection ).to eq( 'bucket' )
-			# TODO: set/retrieve data
+			db[ 'key' ] = false
+
+			db.main
+			expect( db.collection ).to be_nil
+			expect( db['key'] ).to be_truthy
 		end
 
+		it "can be cleared of contents" do
+			db.collection( 'bucket' )
+			10.times {|i| db[i] = true }
+			expect( db[2] ).to be_truthy
+
+			db.clear
+			db.main
+			expect( db['bucket'] ).to be_nil
+		end
 	end
 end
 
diff --git a/spec/data/testdb/mdbx.lck b/tmp/.placeholder
similarity index 100%
rename from spec/data/testdb/mdbx.lck
rename to tmp/.placeholder