diff --git a/.pryrc b/.pryrc
index 7086754..062583e 100644
--- a/.pryrc
+++ b/.pryrc
@@ -11,5 +11,5 @@ rescue Exception => e
 		e.backtrace.join( "\n\t" )
 end
 
-db = MDBX::Database.open( 'tmp/testdb', max_collections: 50 )
+db = MDBX::Database.open( 'tmp/testdb', max_collections: 5 )
 
diff --git a/ext/mdbx_ext/database.c b/ext/mdbx_ext/database.c
index 00c9d29..68fe559 100644
--- a/ext/mdbx_ext/database.c
+++ b/ext/mdbx_ext/database.c
@@ -47,6 +47,20 @@ rmdbx_close_all( rmdbx_db_t *db )
 }
 
 
+/*
+ * Close any open database handle.  Will be automatically
+ * re-opened on next transaction.  This is primarily useful for
+ * switching between subdatabases.
+ */
+void
+rmdbx_close_dbi( rmdbx_db_t *db )
+{
+	if ( ! db->dbi ) return;
+	mdbx_dbi_close( db->env, db->dbi );
+	db->dbi = 0;
+}
+
+
 /*
  * Cleanup a previously allocated DB environment.
  */
@@ -86,6 +100,21 @@ rmdbx_closed_p( VALUE self )
 }
 
 
+/*
+ * call-seq:
+ *    db.in_transaction? #=> false
+ *
+ * Predicate: return true if a transaction (or snapshot)
+ * is currently open.
+ */
+VALUE
+rmdbx_in_transaction_p( VALUE self )
+{
+	UNWRAP_DB( self, db );
+	return db->txn ? Qtrue : Qfalse;
+}
+
+
 /*
  * Open the DB environment handle.
  */
@@ -156,17 +185,15 @@ rmdbx_open_txn( rmdbx_db_t *db, int rwflag )
 
 /*
  * Close any existing database transaction. If there is no
- * active transaction, this is a no-op.
- *
- * FIXME: this needs a conditional no-op for long running
- * transactions, so callers don't have to care/check
+ * 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 ) return;
+	if ( ! db->txn || db->state.retain_txn > -1 ) return;
 
 	switch ( txnflag ) {
 		case RMDBX_TXN_COMMIT:
@@ -180,6 +207,46 @@ rmdbx_close_txn( rmdbx_db_t *db, int txnflag )
 }
 
 
+/*
+ * 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 );
+
+	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;
+}
+
+
 /*
  * call-seq:
  *    db.clear
@@ -382,39 +449,63 @@ rmdbx_stats( VALUE self )
 
 
 /*
- * call-seq:
+ * Gets or sets the sub-database "collection" that read/write operations apply to.
+ * Passing +nil+ sets the database to the main, top-level namespace.
+ * If a block is passed, the collection automatically reverts to the
+ * prior collection when it exits.
+ *
  *    db.collection( 'collection_name' ) # => db
  *    db.collection( nil ) # => db (main)
  *
- * Operate on a sub-database "collection".  Passing +nil+
- * sets the database to the main, top-level namespace.
+ *    db.collection( 'collection_name' ) do
+ *        [ ... ]
+ *    end #=> reverts to the previous collection name
  *
  */
 VALUE
 rmdbx_set_subdb( int argc, VALUE *argv, VALUE self )
 {
 	UNWRAP_DB( self, db );
-	VALUE subdb;
+	VALUE subdb, block;
+	char *prev_db = NULL;
 
-	rb_scan_args( argc, argv, "01", &subdb );
+	rb_scan_args( argc, argv, "01&", &subdb, &block );
 	if ( argc == 0 ) {
 		if ( db->subdb == NULL ) return Qnil;
 		return rb_str_new_cstr( db->subdb );
 	}
 
+	/* All transactions must be closed when switching database handles. */
+	if ( db->txn ) rb_raise( rmdbx_eDatabaseError, "Unable to change collection: finish current transaction" );
+
+	/* Retain the prior database collection if a
+	 * block was passed. */
+	if ( rb_block_given_p() ) {
+		if ( db->subdb != NULL ) {
+			prev_db = (char *) malloc( strlen(db->subdb) + 1 );
+			strcpy( prev_db, db->subdb );
+		}
+	}
+
 	rb_iv_set( self, "@collection", subdb );
 	db->subdb = NIL_P( subdb ) ? NULL : StringValueCStr( subdb );
+	rmdbx_close_dbi( db );
 
-	/* 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.
+	  haven't written anything to the new collection yet.
 	 */
-	if ( db->dbi ) {
-		mdbx_dbi_close( db->env, db->dbi );
-		db->dbi = 0;
+
+	/* Revert to the previous collection after the block is done. */
+	if ( rb_block_given_p() ) {
+		rb_yield( self );
+		if ( db->subdb != prev_db ) {
+			rb_iv_set( self, "@collection", prev_db ? rb_str_new_cstr(prev_db) : Qnil );
+			db->subdb = prev_db;
+			rmdbx_close_dbi( db );
+		}
+		free( prev_db );
 	}
 
 	return self;
@@ -422,15 +513,14 @@ rmdbx_set_subdb( int argc, VALUE *argv, VALUE self )
 
 
 /*
- * call-seq:
+ * Open an existing (or create a new) mdbx database at filesystem
+ * +path+.  In block form, the database is automatically closed.
+ *
  *    MDBX::Database.open( path ) -> db
  *    MDBX::Database.open( path, options ) -> db
  *    MDBX::Database.open( path, options ) do |db|
  *    		db...
- *    end
- *
- * Open an existing (or create a new) mdbx database at filesystem
- * +path+.  In block form, the database is automatically closed.
+ *    end 
  *
  */
 VALUE
@@ -458,7 +548,8 @@ rmdbx_database_initialize( int argc, VALUE *argv, VALUE self )
 	db->cursor = NULL;
 	db->path   = StringValueCStr( path );
 	db->subdb  = NULL;
-	db->state.open = 0;
+	db->state.open       = 0;
+	db->state.retain_txn = -1;
 	db->settings.env_flags       = MDBX_ENV_DEFAULTS;
 	db->settings.mode            = 0644;
 	db->settings.max_collections = 0;
@@ -530,11 +621,16 @@ rmdbx_init_database()
 	rb_define_method( rmdbx_cDatabase, "close", rmdbx_close, 0 );
 	rb_define_method( rmdbx_cDatabase, "reopen", rmdbx_open_env, 0 );
 	rb_define_method( rmdbx_cDatabase, "closed?", rmdbx_closed_p, 0 );
+	rb_define_method( rmdbx_cDatabase, "in_transaction?", rmdbx_in_transaction_p, 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 );
 
+	/* Manually open/close transactions from ruby. */
+	rb_define_protected_method( rmdbx_cDatabase, "open_transaction",  rmdbx_rb_opentxn, 1 );
+	rb_define_protected_method( rmdbx_cDatabase, "close_transaction", rmdbx_rb_closetxn, 1 );
+
 	rb_define_protected_method( rmdbx_cDatabase, "raw_stats", rmdbx_stats, 0 );
 
 	rb_require( "mdbx/database" );
diff --git a/ext/mdbx_ext/mdbx_ext.h b/ext/mdbx_ext/mdbx_ext.h
index 4d159e0..8b2ba84 100644
--- a/ext/mdbx_ext/mdbx_ext.h
+++ b/ext/mdbx_ext/mdbx_ext.h
@@ -31,6 +31,7 @@ struct rmdbx_db {
 
     struct {
        int open;
+       int retain_txn;
     } state;
 
 	char *path;
diff --git a/ext/mdbx_ext/stats.c b/ext/mdbx_ext/stats.c
index e0a5c02..2422762 100644
--- a/ext/mdbx_ext/stats.c
+++ b/ext/mdbx_ext/stats.c
@@ -84,7 +84,7 @@ rmdbx_gather_environment_stats(
 			INT2NUM(menvinfo.mi_recent_txnid) );
 	rb_hash_aset( environ, ID2SYM(rb_intern("last_reader_txnid")),
 			INT2NUM(menvinfo.mi_latter_reader_txnid) );
-	rb_hash_aset( environ, ID2SYM(rb_intern("maximum_readers")),
+	rb_hash_aset( environ, ID2SYM(rb_intern("max_readers")),
 			INT2NUM(menvinfo.mi_maxreaders) );
 	rb_hash_aset( environ, ID2SYM(rb_intern("readers_in_use")),
 			INT2NUM(menvinfo.mi_numreaders) );
@@ -183,8 +183,7 @@ rmdbx_gather_stats( rmdbx_db_t *db )
 	rmdbx_gather_environment_stats( stat, mstat, menvinfo );
 	rmdbx_gather_reader_stats( db, stat, mstat, menvinfo );
 
-	/* database and subdatabases */
-
+	/* TODO: database and subdatabase stats */
 
 	return stat;
 }
diff --git a/lib/mdbx/database.rb b/lib/mdbx/database.rb
index 8ac0573..3f7d0b9 100644
--- a/lib/mdbx/database.rb
+++ b/lib/mdbx/database.rb
@@ -18,8 +18,6 @@ class MDBX::Database
 	###        db[ 'key' ] #=> value
 	###    end
 	###
-	### FIXME: document all options!
-	###
 	def self::open( *args, &block )
 		db = new( *args )
 
@@ -49,9 +47,11 @@ class MDBX::Database
 	attr_reader :path
 
 	# A Proc for automatically serializing values.
+	# Defaults to +Marshal.dump+.
 	attr_accessor :serializer
 
 	# A Proc for automatically deserializing values.
+	# Defaults to +Marshal.load+.
 	attr_accessor :deserializer
 
 
@@ -65,6 +65,56 @@ class MDBX::Database
 	alias_method :namespace, :collection
 
 
+	### Open a new mdbx read/write transaction.  In block form,
+	### the transaction is automatically committed.
+	###
+	### Raising a MDBX::Rollback exception from within the block
+	### automatically rolls the transaction back.
+	###
+	def transaction( commit: true, &block )
+		self.open_transaction( commit )
+		yield self if block_given?
+
+		return self
+
+	rescue MDBX::Rollback
+		commit = false
+		self.rollback
+	rescue
+		commit = false
+		self.rollback
+		raise
+	ensure
+		if block_given?
+			commit ? self.commit : self.rollback
+		end
+	end
+
+
+	### Open a new mdbx read only snapshot.  In block form,
+	### the snapshot is automatically closed.
+	###
+	def snapshot( &block )
+		self.transaction( commit: false, &block )
+	end
+
+
+	### Close any open transactions, abandoning all changes.
+	###
+	def rollback
+		return self.close_transaction( false )
+	end
+	alias_method :abort, :rollback
+
+
+	### Close any open transactions, writing all changes.
+	###
+	def commit
+		return self.close_transaction( true )
+	end
+	alias_method :save, :commit
+
+
 	### Return a hash of various metadata for the current database.
 	###
 	def statistics
diff --git a/spec/mdbx/database_spec.rb b/spec/mdbx/database_spec.rb
index b6feab8..90a6706 100644
--- a/spec/mdbx/database_spec.rb
+++ b/spec/mdbx/database_spec.rb
@@ -1,4 +1,5 @@
 #!/usr/bin/env rspec -cfd
+# vim: set nosta noet ts=4 sw=4 ft=ruby:
 
 require_relative '../lib/helper'
 
@@ -113,6 +114,12 @@ RSpec.describe( MDBX::Database ) do
 			expect( db['key'] ).to be_truthy
 		end
 
+		it "revert back to the previous collection when used in a block" do
+			expect( db.collection ).to be_nil
+			db.collection( 'bucket' ) { 'no-op' }
+			expect( db.collection ).to be_nil
+		end
+
 		it "can be cleared of contents" do
 			db.collection( 'bucket' )
 			10.times {|i| db[i] = true }
diff --git a/spec/mdbx/stats_spec.rb b/spec/mdbx/stats_spec.rb
new file mode 100644
index 0000000..4d45520
--- /dev/null
+++ b/spec/mdbx/stats_spec.rb
@@ -0,0 +1,57 @@
+#!/usr/bin/env rspec -cfd
+# vim: set nosta noet ts=4 sw=4 ft=ruby:
+
+require_relative '../lib/helper'
+
+
+RSpec.fdescribe( MDBX::Database ) do
+
+	let!( :db ) { described_class.open( TEST_DATABASE.to_s, max_readers: 500 ) }
+
+	let( :stats ) { db.statistics }
+
+	after( :each ) do
+		db.close
+	end
+
+	it "returns the configured max_readers" do
+		expect( stats.dig(:environment, :max_readers) ).to be >= 500
+	end
+
+	it "returns compile time flags and options" do
+		build = stats[ :build ]
+		expect( build.keys.size ).to be( 4 )
+		expect( build.keys ).to include( :compiler, :flags, :options, :target )
+		expect( build[:compiler] ).to be_a( String )
+		expect( build[:flags] ).to be_a( String )
+		expect( build[:target] ).to be_a( String )
+		expect( build[:options] ).to be_a( Hash )
+	end
+
+end
+
+
+__END__
+{:environment=>
+  {:pagesize=>4096,
+     :last_txnid=>125,
+     :last_reader_txnid=>125,
+     :maximum_readers=>122,
+     :readers_in_use=>1,
+     :datafile=>
+      {:size_current=>65536,
+	       :pages=>16,
+	       :type=>"dynamic",
+	       :size_lower=>12288,
+	       :size_upper=>1048576,
+	       :growth_step=>65536,
+	       :shrink_threshold=>131072}},
+ :readers=>
+  [{:slot=>0,
+      :pid=>45436,
+      :thread=>34374651904,
+      :txnid=>0,
+      :lag=>0,
+      :bytes_used=>0,
+      :bytes_retired=>0}]}
+}