diff --git a/src/database/database_view.rs b/src/database/database_view.rs
index c6c30d39f..671d18433 100644
--- a/src/database/database_view.rs
+++ b/src/database/database_view.rs
@@ -1,4 +1,5 @@
 use std::error::Error;
+use std::ops::Deref;
 use std::{fmt, marker};
 
 use rocksdb::rocksdb::{DB, DBVector, Snapshot, SeekKey};
@@ -14,14 +15,18 @@ use crate::database::schema::Schema;
 use crate::rank::QueryBuilder;
 use crate::DocumentId;
 
-pub struct DatabaseView<'a> {
-    snapshot: Snapshot<&'a DB>,
+pub struct DatabaseView<D>
+where D: Deref<Target=DB>
+{
+    snapshot: Snapshot<D>,
     blob: PositiveBlob,
     schema: Schema,
 }
 
-impl<'a> DatabaseView<'a> {
-    pub fn new(snapshot: Snapshot<&'a DB>) -> Result<DatabaseView, Box<Error>> {
+impl<D> DatabaseView<D>
+where D: Deref<Target=DB>
+{
+    pub fn new(snapshot: Snapshot<D>) -> Result<DatabaseView<D>, Box<Error>> {
         let schema = retrieve_data_schema(&snapshot)?;
         let blob = retrieve_data_index(&snapshot)?;
         Ok(DatabaseView { snapshot, blob, schema })
@@ -35,11 +40,11 @@ impl<'a> DatabaseView<'a> {
         &self.blob
     }
 
-    pub fn into_snapshot(self) -> Snapshot<&'a DB> {
+    pub fn into_snapshot(self) -> Snapshot<D> {
         self.snapshot
     }
 
-    pub fn snapshot(&self) -> &Snapshot<&'a DB> {
+    pub fn snapshot(&self) -> &Snapshot<D> {
         &self.snapshot
     }
 
@@ -47,20 +52,20 @@ impl<'a> DatabaseView<'a> {
         Ok(self.snapshot.get(key)?)
     }
 
-    pub fn query_builder(&self) -> Result<QueryBuilder<Box<dyn Criterion>>, Box<Error>> {
+    pub fn query_builder(&self) -> Result<QueryBuilder<D, Box<dyn Criterion<D>>>, Box<Error>> {
         QueryBuilder::new(self)
     }
 
     // TODO create an enum error type
-    pub fn retrieve_document<D>(&self, id: DocumentId) -> Result<D, Box<Error>>
-    where D: DeserializeOwned
+    pub fn retrieve_document<T>(&self, id: DocumentId) -> Result<T, Box<Error>>
+    where T: DeserializeOwned
     {
         let mut deserializer = Deserializer::new(&self.snapshot, &self.schema, id);
-        Ok(D::deserialize(&mut deserializer)?)
+        Ok(T::deserialize(&mut deserializer)?)
     }
 
-    pub fn retrieve_documents<D, I>(&self, ids: I) -> DocumentIter<D, I::IntoIter>
-    where D: DeserializeOwned,
+    pub fn retrieve_documents<T, I>(&self, ids: I) -> DocumentIter<D, T, I::IntoIter>
+    where T: DeserializeOwned,
           I: IntoIterator<Item=DocumentId>,
     {
         DocumentIter {
@@ -71,7 +76,9 @@ impl<'a> DatabaseView<'a> {
     }
 }
 
-impl<'a> fmt::Debug for DatabaseView<'a> {
+impl<D> fmt::Debug for DatabaseView<D>
+where D: Deref<Target=DB>
+{
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut options = ReadOptions::new();
         let lower = DocumentKey::new(0);
@@ -102,17 +109,20 @@ impl<'a> fmt::Debug for DatabaseView<'a> {
 }
 
 // TODO this is just an iter::Map !!!
-pub struct DocumentIter<'a, D, I> {
-    database_view: &'a DatabaseView<'a>,
+pub struct DocumentIter<'a, D, T, I>
+where D: Deref<Target=DB>
+{
+    database_view: &'a DatabaseView<D>,
     document_ids: I,
-    _phantom: marker::PhantomData<D>,
+    _phantom: marker::PhantomData<T>,
 }
 
-impl<'a, D, I> Iterator for DocumentIter<'a, D, I>
-where D: DeserializeOwned,
+impl<'a, D, T, I> Iterator for DocumentIter<'a, D, T, I>
+where D: Deref<Target=DB>,
+      T: DeserializeOwned,
       I: Iterator<Item=DocumentId>,
 {
-    type Item = Result<D, Box<Error>>;
+    type Item = Result<T, Box<Error>>;
 
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.document_ids.size_hint()
@@ -126,13 +136,15 @@ where D: DeserializeOwned,
     }
 }
 
-impl<'a, D, I> ExactSizeIterator for DocumentIter<'a, D, I>
-where D: DeserializeOwned,
+impl<'a, D, T, I> ExactSizeIterator for DocumentIter<'a, D, T, I>
+where D: Deref<Target=DB>,
+      T: DeserializeOwned,
       I: ExactSizeIterator + Iterator<Item=DocumentId>,
 { }
 
-impl<'a, D, I> DoubleEndedIterator for DocumentIter<'a, D, I>
-where D: DeserializeOwned,
+impl<'a, D, T, I> DoubleEndedIterator for DocumentIter<'a, D, T, I>
+where D: Deref<Target=DB>,
+      T: DeserializeOwned,
       I: DoubleEndedIterator + Iterator<Item=DocumentId>,
 {
     fn next_back(&mut self) -> Option<Self::Item> {
diff --git a/src/database/deserializer.rs b/src/database/deserializer.rs
index 11e65896f..26d74984d 100644
--- a/src/database/deserializer.rs
+++ b/src/database/deserializer.rs
@@ -1,4 +1,5 @@
 use std::error::Error;
+use std::ops::Deref;
 use std::fmt;
 
 use rocksdb::rocksdb::{DB, Snapshot, SeekKey};
@@ -11,19 +12,25 @@ use crate::database::document_key::{DocumentKey, DocumentKeyAttr};
 use crate::database::schema::Schema;
 use crate::DocumentId;
 
-pub struct Deserializer<'a> {
-    snapshot: &'a Snapshot<&'a DB>,
+pub struct Deserializer<'a, D>
+where D: Deref<Target=DB>
+{
+    snapshot: &'a Snapshot<D>,
     schema: &'a Schema,
     document_id: DocumentId,
 }
 
-impl<'a> Deserializer<'a> {
-    pub fn new(snapshot: &'a Snapshot<&DB>, schema: &'a Schema, doc: DocumentId) -> Self {
+impl<'a, D> Deserializer<'a, D>
+where D: Deref<Target=DB>
+{
+    pub fn new(snapshot: &'a Snapshot<D>, schema: &'a Schema, doc: DocumentId) -> Self {
         Deserializer { snapshot, schema, document_id: doc }
     }
 }
 
-impl<'de, 'a, 'b> de::Deserializer<'de> for &'b mut Deserializer<'a> {
+impl<'de, 'a, 'b, D> de::Deserializer<'de> for &'b mut Deserializer<'a, D>
+where D: Deref<Target=DB>
+{
     type Error = DeserializerError;
 
     fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
diff --git a/src/database/mod.rs b/src/database/mod.rs
index c347b11ce..8b2b89544 100644
--- a/src/database/mod.rs
+++ b/src/database/mod.rs
@@ -1,6 +1,7 @@
 use std::error::Error;
 use std::path::Path;
 use std::ops::Deref;
+use std::sync::Arc;
 use std::fmt;
 
 use rocksdb::rocksdb_options::{DBOptions, IngestExternalFileOptions, ColumnFamilyOptions};
@@ -42,7 +43,8 @@ where D: Deref<Target=DB>
     }
 }
 
-pub struct Database(DB);
+#[derive(Clone)]
+pub struct Database(Arc<DB>);
 
 impl Database {
     pub fn create<P: AsRef<Path>>(path: P, schema: Schema) -> Result<Database, Box<Error>> {
@@ -66,7 +68,7 @@ impl Database {
         schema.write_to(&mut schema_bytes)?;
         db.put(DATA_SCHEMA, &schema_bytes)?;
 
-        Ok(Database(db))
+        Ok(Database(Arc::new(db)))
     }
 
     pub fn open<P: AsRef<Path>>(path: P) -> Result<Database, Box<Error>> {
@@ -86,7 +88,7 @@ impl Database {
             None => return Err(String::from("Database does not contain a schema").into()),
         };
 
-        Ok(Database(db))
+        Ok(Database(Arc::new(db)))
     }
 
     pub fn ingest_update_file(&self, update: Update) -> Result<(), Box<Error>> {
@@ -114,10 +116,15 @@ impl Database {
         Ok(self.0.flush(true)?)
     }
 
-    pub fn view(&self) -> Result<DatabaseView, Box<Error>> {
+    pub fn view(&self) -> Result<DatabaseView<&DB>, Box<Error>> {
         let snapshot = self.0.snapshot();
         DatabaseView::new(snapshot)
     }
+
+    pub fn view_arc(&self) -> Result<DatabaseView<Arc<DB>>, Box<Error>> {
+        let snapshot = Snapshot::new(self.0.clone());
+        DatabaseView::new(snapshot)
+    }
 }
 
 impl fmt::Debug for Database {
diff --git a/src/rank/criterion/exact.rs b/src/rank/criterion/exact.rs
index 9ea59eae3..041a6ae67 100644
--- a/src/rank/criterion/exact.rs
+++ b/src/rank/criterion/exact.rs
@@ -1,5 +1,7 @@
 use std::cmp::Ordering;
+use std::ops::Deref;
 
+use rocksdb::DB;
 use group_by::GroupBy;
 
 use crate::rank::{match_query_index, Document};
@@ -20,8 +22,10 @@ fn number_exact_matches(matches: &[Match]) -> usize {
 #[derive(Debug, Clone, Copy)]
 pub struct Exact;
 
-impl Criterion for Exact {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for Exact
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = number_exact_matches(&lhs.matches);
         let rhs = number_exact_matches(&rhs.matches);
 
diff --git a/src/rank/criterion/mod.rs b/src/rank/criterion/mod.rs
index a4590ae90..2993f1ba8 100644
--- a/src/rank/criterion/mod.rs
+++ b/src/rank/criterion/mod.rs
@@ -5,8 +5,11 @@ mod sum_of_words_attribute;
 mod sum_of_words_position;
 mod exact;
 
-use std::vec;
 use std::cmp::Ordering;
+use std::ops::Deref;
+use std::vec;
+
+use rocksdb::DB;
 
 use crate::database::DatabaseView;
 use crate::rank::Document;
@@ -20,32 +23,38 @@ pub use self::{
     exact::Exact,
 };
 
-pub trait Criterion {
+pub trait Criterion<D>
+where D: Deref<Target=DB>
+{
     #[inline]
-    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> Ordering;
+    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> Ordering;
 
     #[inline]
-    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> bool {
+    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> bool {
         self.evaluate(lhs, rhs, view) == Ordering::Equal
     }
 }
 
-impl<'a, T: Criterion + ?Sized> Criterion for &'a T {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> Ordering {
+impl<'a, D, T: Criterion<D> + ?Sized> Criterion<D> for &'a T
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> Ordering {
         (**self).evaluate(lhs, rhs, view)
     }
 
-    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> bool {
+    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> bool {
         (**self).eq(lhs, rhs, view)
     }
 }
 
-impl<T: Criterion + ?Sized> Criterion for Box<T> {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> Ordering {
+impl<D, T: Criterion<D> + ?Sized> Criterion<D> for Box<T>
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> Ordering {
         (**self).evaluate(lhs, rhs, view)
     }
 
-    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView) -> bool {
+    fn eq(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> bool {
         (**self).eq(lhs, rhs, view)
     }
 }
@@ -53,15 +62,19 @@ impl<T: Criterion + ?Sized> Criterion for Box<T> {
 #[derive(Debug, Clone, Copy)]
 pub struct DocumentId;
 
-impl Criterion for DocumentId {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for DocumentId
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         lhs.id.cmp(&rhs.id)
     }
 }
 
 // TODO there is too much Box here, can we use
 //      static references or static closures
-pub fn default() -> Vec<Box<dyn Criterion>> {
+pub fn default<D>() -> Vec<Box<dyn Criterion<D>>>
+where D: Deref<Target=DB>
+{
     vec![
         Box::new(SumOfTypos),
         Box::new(NumberOfWords),
diff --git a/src/rank/criterion/number_of_words.rs b/src/rank/criterion/number_of_words.rs
index b20586f39..855d997ba 100644
--- a/src/rank/criterion/number_of_words.rs
+++ b/src/rank/criterion/number_of_words.rs
@@ -1,5 +1,7 @@
 use std::cmp::Ordering;
+use std::ops::Deref;
 
+use rocksdb::DB;
 use group_by::GroupBy;
 
 use crate::rank::{match_query_index, Document};
@@ -15,8 +17,10 @@ fn number_of_query_words(matches: &[Match]) -> usize {
 #[derive(Debug, Clone, Copy)]
 pub struct NumberOfWords;
 
-impl Criterion for NumberOfWords {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for NumberOfWords
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = number_of_query_words(&lhs.matches);
         let rhs = number_of_query_words(&rhs.matches);
 
diff --git a/src/rank/criterion/sum_of_typos.rs b/src/rank/criterion/sum_of_typos.rs
index 5cbd4bac1..a7074bd86 100644
--- a/src/rank/criterion/sum_of_typos.rs
+++ b/src/rank/criterion/sum_of_typos.rs
@@ -1,4 +1,7 @@
 use std::cmp::Ordering;
+use std::ops::Deref;
+
+use rocksdb::DB;
 
 use group_by::GroupBy;
 
@@ -25,8 +28,10 @@ fn sum_matches_typos(matches: &[Match]) -> i8 {
 #[derive(Debug, Clone, Copy)]
 pub struct SumOfTypos;
 
-impl Criterion for SumOfTypos {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for SumOfTypos
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = sum_matches_typos(&lhs.matches);
         let rhs = sum_matches_typos(&rhs.matches);
 
diff --git a/src/rank/criterion/sum_of_words_attribute.rs b/src/rank/criterion/sum_of_words_attribute.rs
index d373dedef..800fe7c7f 100644
--- a/src/rank/criterion/sum_of_words_attribute.rs
+++ b/src/rank/criterion/sum_of_words_attribute.rs
@@ -1,5 +1,7 @@
 use std::cmp::Ordering;
+use std::ops::Deref;
 
+use rocksdb::DB;
 use group_by::GroupBy;
 
 use crate::database::DatabaseView;
@@ -19,8 +21,10 @@ fn sum_matches_attributes(matches: &[Match]) -> u8 {
 #[derive(Debug, Clone, Copy)]
 pub struct SumOfWordsAttribute;
 
-impl Criterion for SumOfWordsAttribute {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for SumOfWordsAttribute
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = sum_matches_attributes(&lhs.matches);
         let rhs = sum_matches_attributes(&rhs.matches);
 
diff --git a/src/rank/criterion/sum_of_words_position.rs b/src/rank/criterion/sum_of_words_position.rs
index cd41d5b72..2a54b1098 100644
--- a/src/rank/criterion/sum_of_words_position.rs
+++ b/src/rank/criterion/sum_of_words_position.rs
@@ -1,5 +1,7 @@
 use std::cmp::Ordering;
+use std::ops::Deref;
 
+use rocksdb::DB;
 use group_by::GroupBy;
 
 use crate::database::DatabaseView;
@@ -19,8 +21,10 @@ fn sum_matches_attribute_index(matches: &[Match]) -> u32 {
 #[derive(Debug, Clone, Copy)]
 pub struct SumOfWordsPosition;
 
-impl Criterion for SumOfWordsPosition {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for SumOfWordsPosition
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = sum_matches_attribute_index(&lhs.matches);
         let rhs = sum_matches_attribute_index(&rhs.matches);
 
diff --git a/src/rank/criterion/words_proximity.rs b/src/rank/criterion/words_proximity.rs
index abbd0e99f..14eb1ad0e 100644
--- a/src/rank/criterion/words_proximity.rs
+++ b/src/rank/criterion/words_proximity.rs
@@ -1,5 +1,7 @@
 use std::cmp::{self, Ordering};
+use std::ops::Deref;
 
+use rocksdb::DB;
 use group_by::GroupBy;
 
 use crate::rank::{match_query_index, Document};
@@ -49,8 +51,10 @@ fn matches_proximity(matches: &[Match]) -> u32 {
 #[derive(Debug, Clone, Copy)]
 pub struct WordsProximity;
 
-impl Criterion for WordsProximity {
-    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView) -> Ordering {
+impl<D> Criterion<D> for WordsProximity
+where D: Deref<Target=DB>
+{
+    fn evaluate(&self, lhs: &Document, rhs: &Document, _: &DatabaseView<D>) -> Ordering {
         let lhs = matches_proximity(&lhs.matches);
         let rhs = matches_proximity(&rhs.matches);
 
diff --git a/src/rank/query_builder.rs b/src/rank/query_builder.rs
index 1a43d30fb..2d9795a55 100644
--- a/src/rank/query_builder.rs
+++ b/src/rank/query_builder.rs
@@ -1,11 +1,12 @@
+use std::ops::{Deref, Range};
 use std::error::Error;
 use std::hash::Hash;
-use std::ops::Range;
 use std::{mem, vec, str};
 
 use group_by::GroupByMut;
 use hashbrown::HashMap;
 use fst::Streamer;
+use rocksdb::DB;
 
 use crate::automaton::{self, DfaExt, AutomatonExt};
 use crate::rank::criterion::{self, Criterion};
@@ -23,19 +24,25 @@ fn split_whitespace_automatons(query: &str) -> Vec<DfaExt> {
     automatons
 }
 
-pub struct QueryBuilder<'a, C> {
-    view: &'a DatabaseView<'a>,
+pub struct QueryBuilder<'a, D, C>
+where D: Deref<Target=DB>
+{
+    view: &'a DatabaseView<D>,
     criteria: Vec<C>,
 }
 
-impl<'a> QueryBuilder<'a, Box<dyn Criterion>> {
-    pub fn new(view: &'a DatabaseView<'a>) -> Result<Self, Box<Error>> {
+impl<'a, D> QueryBuilder<'a, D, Box<dyn Criterion<D>>>
+where D: Deref<Target=DB>
+{
+    pub fn new(view: &'a DatabaseView<D>) -> Result<Self, Box<Error>> {
         QueryBuilder::with_criteria(view, criterion::default())
     }
 }
 
-impl<'a, C> QueryBuilder<'a, C> {
-    pub fn with_criteria(view: &'a DatabaseView<'a>, criteria: Vec<C>) -> Result<Self, Box<Error>> {
+impl<'a, D, C> QueryBuilder<'a, D, C>
+where D: Deref<Target=DB>
+{
+    pub fn with_criteria(view: &'a DatabaseView<D>, criteria: Vec<C>) -> Result<Self, Box<Error>> {
         Ok(QueryBuilder { view, criteria })
     }
 
@@ -44,7 +51,7 @@ impl<'a, C> QueryBuilder<'a, C> {
         self
     }
 
-    pub fn with_distinct<F>(self, function: F, size: usize) -> DistinctQueryBuilder<'a, F, C> {
+    pub fn with_distinct<F>(self, function: F, size: usize) -> DistinctQueryBuilder<'a, D, F, C> {
         DistinctQueryBuilder {
             inner: self,
             function: function,
@@ -92,8 +99,9 @@ impl<'a, C> QueryBuilder<'a, C> {
     }
 }
 
-impl<'a, C> QueryBuilder<'a, C>
-where C: Criterion
+impl<'a, D, C> QueryBuilder<'a, D, C>
+where D: Deref<Target=DB>,
+      C: Criterion<D>
 {
     pub fn query(&self, query: &str, limit: usize) -> Vec<Document> {
         let mut documents = self.query_all(query);
@@ -119,16 +127,19 @@ where C: Criterion
     }
 }
 
-pub struct DistinctQueryBuilder<'a, F, C> {
-    inner: QueryBuilder<'a, C>,
+pub struct DistinctQueryBuilder<'a, D, F, C>
+where D: Deref<Target=DB>
+{
+    inner: QueryBuilder<'a, D, C>,
     function: F,
     size: usize,
 }
 
-impl<'a, F, K, C> DistinctQueryBuilder<'a, F, C>
-where F: Fn(DocumentId, &DatabaseView) -> Option<K>,
+impl<'a, D, F, K, C> DistinctQueryBuilder<'a, D, F, C>
+where D: Deref<Target=DB>,
+      F: Fn(DocumentId, &DatabaseView<D>) -> Option<K>,
       K: Hash + Eq,
-      C: Criterion,
+      C: Criterion<D>,
 {
     pub fn query(&self, query: &str, range: Range<usize>) -> Vec<Document> {
         let mut documents = self.inner.query_all(query);