diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index e0d2a7af..297923c9 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -14,7 +14,7 @@ edition = "2018"
 
 [dependencies]
 lazy_static = "1"
-rocksdb = { version = "0.12", optional = true }
+rocksdb = { version = "0.13", optional = true }
 byteorder = { version = "1", features = ["i128"] }
 quick-xml = "0.17"
 ordered-float = "1"
diff --git a/lib/src/sparql/eval.rs b/lib/src/sparql/eval.rs
index 395ac207..6ca2e14f 100644
--- a/lib/src/sparql/eval.rs
+++ b/lib/src/sparql/eval.rs
@@ -29,7 +29,6 @@ use std::fmt::Write;
 use std::hash::Hash;
 use std::iter::Iterator;
 use std::iter::{empty, once};
-use std::ops::Deref;
 use std::str;
 use std::sync::Mutex;
 
@@ -1451,10 +1450,7 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
         }
     }
 
-    fn to_simple_string(
-        &self,
-        term: EncodedTerm,
-    ) -> Option<<DatasetView<S> as StrLookup>::StrType> {
+    fn to_simple_string(&self, term: EncodedTerm) -> Option<String> {
         if let EncodedTerm::StringLiteral { value_id } = term {
             self.dataset.get_str(value_id).ok()?
         } else {
@@ -1470,7 +1466,7 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
         }
     }
 
-    fn to_string(&self, term: EncodedTerm) -> Option<<DatasetView<S> as StrLookup>::StrType> {
+    fn to_string(&self, term: EncodedTerm) -> Option<String> {
         match term {
             EncodedTerm::StringLiteral { value_id }
             | EncodedTerm::LangStringLiteral { value_id, .. } => {
@@ -1480,10 +1476,7 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
         }
     }
 
-    fn to_string_and_language(
-        &self,
-        term: EncodedTerm,
-    ) -> Option<(<DatasetView<S> as StrLookup>::StrType, Option<u128>)> {
+    fn to_string_and_language(&self, term: EncodedTerm) -> Option<(String, Option<u128>)> {
         match term {
             EncodedTerm::StringLiteral { value_id } => {
                 Some((self.dataset.get_str(value_id).ok()??, None))
@@ -1533,11 +1526,7 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
         &self,
         arg1: EncodedTerm,
         arg2: EncodedTerm,
-    ) -> Option<(
-        <DatasetView<S> as StrLookup>::StrType,
-        <DatasetView<S> as StrLookup>::StrType,
-        Option<u128>,
-    )> {
+    ) -> Option<(String, String, Option<u128>)> {
         let (value1, language1) = self.to_string_and_language(arg1)?;
         let (value2, language2) = self.to_string_and_language(arg2)?;
         if language2.is_none() || language1 == language2 {
@@ -1893,40 +1882,6 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
     }
 }
 
-pub enum StringOrStoreString<S: Deref<Target = str> + ToString + Into<String>> {
-    String(String),
-    Store(S),
-}
-
-impl<S: Deref<Target = str> + ToString + Into<String>> Deref for StringOrStoreString<S> {
-    type Target = str;
-
-    fn deref(&self) -> &str {
-        match self {
-            StringOrStoreString::String(s) => &*s,
-            StringOrStoreString::Store(s) => &*s,
-        }
-    }
-}
-
-impl<S: Deref<Target = str> + ToString + Into<String>> ToString for StringOrStoreString<S> {
-    fn to_string(&self) -> String {
-        match self {
-            StringOrStoreString::String(s) => s.to_string(),
-            StringOrStoreString::Store(s) => s.to_string(),
-        }
-    }
-}
-
-impl<S: Deref<Target = str> + ToString + Into<String>> From<StringOrStoreString<S>> for String {
-    fn from(string: StringOrStoreString<S>) -> Self {
-        match string {
-            StringOrStoreString::String(s) => s,
-            StringOrStoreString::Store(s) => s.into(),
-        }
-    }
-}
-
 enum NumericBinaryOperands {
     Float(f32, f32),
     Double(f64, f64),
diff --git a/lib/src/sparql/plan.rs b/lib/src/sparql/plan.rs
index 7b8a98a3..b07afbe3 100644
--- a/lib/src/sparql/plan.rs
+++ b/lib/src/sparql/plan.rs
@@ -1,4 +1,3 @@
-use crate::sparql::eval::StringOrStoreString;
 use crate::sparql::model::Variable;
 use crate::sparql::GraphPattern;
 use crate::store::numeric_encoder::{
@@ -493,16 +492,12 @@ impl<S: StoreConnection> DatasetView<S> {
 }
 
 impl<S: StoreConnection> StrLookup for DatasetView<S> {
-    type StrType = StringOrStoreString<S::StrType>;
-
-    fn get_str(&self, id: u128) -> Result<Option<StringOrStoreString<S::StrType>>> {
-        Ok(if let Some(value) = self.extra.borrow().get_str(id)? {
-            Some(StringOrStoreString::String(value))
-        } else if let Some(value) = self.store.get_str(id)? {
-            Some(StringOrStoreString::Store(value))
+    fn get_str(&self, id: u128) -> Result<Option<String>> {
+        if let Some(value) = self.extra.borrow().get_str(id)? {
+            Ok(Some(value))
         } else {
-            None
-        })
+            self.store.get_str(id)
+        }
     }
 }
 
diff --git a/lib/src/store/memory.rs b/lib/src/store/memory.rs
index 95bf9d47..a950672c 100644
--- a/lib/src/store/memory.rs
+++ b/lib/src/store/memory.rs
@@ -77,8 +77,6 @@ impl<'a> Store for &'a MemoryStore {
 }
 
 impl<'a> StrLookup for &'a MemoryStore {
-    type StrType = String;
-
     fn get_str(&self, id: u128) -> Result<Option<String>> {
         self.indexes()?.str_store.get_str(id)
     }
diff --git a/lib/src/store/numeric_encoder.rs b/lib/src/store/numeric_encoder.rs
index db8c5b95..0f574a75 100644
--- a/lib/src/store/numeric_encoder.rs
+++ b/lib/src/store/numeric_encoder.rs
@@ -16,7 +16,6 @@ use std::collections::HashMap;
 use std::io::Read;
 use std::io::Write;
 use std::mem::size_of;
-use std::ops::Deref;
 use std::str;
 
 const EMPTY_STRING_ID: u128 = 0x7e42_f8ec_9809_80e9_04b2_008f_d98c_1dd4;
@@ -693,9 +692,7 @@ impl<W: Write> TermWriter for W {
 }
 
 pub trait StrLookup {
-    type StrType: Deref<Target = str> + ToString + Into<String>;
-
-    fn get_str(&self, id: u128) -> Result<Option<Self::StrType>>;
+    fn get_str(&self, id: u128) -> Result<Option<String>>;
 }
 
 pub trait StrContainer {
@@ -733,8 +730,6 @@ impl Default for MemoryStrStore {
 }
 
 impl StrLookup for MemoryStrStore {
-    type StrType = String;
-
     fn get_str(&self, id: u128) -> Result<Option<String>> {
         //TODO: avoid copy by adding a lifetime limit to get_str
         Ok(self.id2str.get(&id).cloned())
@@ -1121,7 +1116,7 @@ impl<S: StrLookup> Decoder for S {
     }
 }
 
-fn get_required_str<S: StrLookup>(lookup: &S, id: u128) -> Result<S::StrType> {
+fn get_required_str(lookup: &impl StrLookup, id: u128) -> Result<String> {
     lookup.get_str(id)?.ok_or_else(|| {
         format_err!(
             "Not able to find the string with id {} in the string store",
diff --git a/lib/src/store/rocksdb.rs b/lib/src/store/rocksdb.rs
index c0c22960..615c43b5 100644
--- a/lib/src/store/rocksdb.rs
+++ b/lib/src/store/rocksdb.rs
@@ -2,17 +2,10 @@ use crate::store::numeric_encoder::*;
 use crate::store::{Store, StoreConnection, StoreRepositoryConnection, StoreTransaction};
 use crate::{Repository, Result};
 use failure::format_err;
-use rocksdb::ColumnFamily;
-use rocksdb::DBCompactionStyle;
-use rocksdb::DBRawIterator;
-use rocksdb::DBVector;
-use rocksdb::Options;
-use rocksdb::WriteBatch;
-use rocksdb::DB;
+use rocksdb::*;
 use std::io::Cursor;
 use std::iter::{empty, once};
 use std::mem::swap;
-use std::ops::Deref;
 use std::path::Path;
 use std::str;
 
@@ -77,13 +70,13 @@ struct RocksDbStore {
 #[derive(Clone)]
 pub struct RocksDbStoreConnection<'a> {
     store: &'a RocksDbStore,
-    id2str_cf: ColumnFamily<'a>,
-    spog_cf: ColumnFamily<'a>,
-    posg_cf: ColumnFamily<'a>,
-    ospg_cf: ColumnFamily<'a>,
-    gspo_cf: ColumnFamily<'a>,
-    gpos_cf: ColumnFamily<'a>,
-    gosp_cf: ColumnFamily<'a>,
+    id2str_cf: &'a ColumnFamily,
+    spog_cf: &'a ColumnFamily,
+    posg_cf: &'a ColumnFamily,
+    ospg_cf: &'a ColumnFamily,
+    gspo_cf: &'a ColumnFamily,
+    gpos_cf: &'a ColumnFamily,
+    gosp_cf: &'a ColumnFamily,
 }
 
 impl RocksDbRepository {
@@ -139,14 +132,12 @@ impl<'a> Store for &'a RocksDbStore {
 }
 
 impl StrLookup for RocksDbStoreConnection<'_> {
-    type StrType = RocksString;
-
-    fn get_str(&self, id: u128) -> Result<Option<RocksString>> {
+    fn get_str(&self, id: u128) -> Result<Option<String>> {
         Ok(self
             .store
             .db
             .get_cf(self.id2str_cf, &id.to_le_bytes())?
-            .map(|v| RocksString { vec: v }))
+            .map(|v| unsafe { String::from_utf8_unchecked(v) }))
     }
 }
 
@@ -164,7 +155,11 @@ impl<'a> StoreConnection for RocksDbStoreConnection<'a> {
     fn contains(&self, quad: &EncodedQuad) -> Result<bool> {
         let mut buffer = Vec::with_capacity(4 * WRITTEN_TERM_MAX_SIZE);
         buffer.write_spog_quad(quad)?;
-        Ok(self.store.db.get_cf(self.spog_cf, &buffer)?.is_some())
+        Ok(self
+            .store
+            .db
+            .get_pinned_cf(self.spog_cf, &buffer)?
+            .is_some())
     }
 
     fn quads_for_pattern<'b>(
@@ -417,7 +412,7 @@ impl<'a> RocksDbStoreConnection<'a> {
 
     fn inner_quads(
         &self,
-        cf: ColumnFamily,
+        cf: &ColumnFamily,
         prefix: Vec<u8>,
         decode: impl Fn(&[u8]) -> Result<EncodedQuad> + 'a,
     ) -> Result<impl Iterator<Item = Result<EncodedQuad>> + 'a> {
@@ -532,7 +527,7 @@ impl<'a> StoreTransaction for RocksDbStoreTransaction<'a> {
     }
 }
 
-fn get_cf<'a>(db: &'a DB, name: &str) -> Result<ColumnFamily<'a>> {
+fn get_cf<'a>(db: &'a DB, name: &str) -> Result<&'a ColumnFamily> {
     db.cf_handle(name)
         .ok_or_else(|| format_err!("column family {} not found", name))
 }
@@ -578,15 +573,13 @@ impl<'a, F: Fn(&[u8]) -> Result<EncodedQuad>> Iterator for DecodingIndexIterator
 
     fn next(&mut self) -> Option<Result<EncodedQuad>> {
         if self.iter.valid() {
-            let result = unsafe {
-                self.iter.key_inner().and_then(|key| {
-                    if key.starts_with(&self.prefix) {
-                        Some((self.decode)(key))
-                    } else {
-                        None
-                    }
-                })
-            };
+            let result = self.iter.key().and_then(|key| {
+                if key.starts_with(&self.prefix) {
+                    Some((self.decode)(key))
+                } else {
+                    None
+                }
+            });
             self.iter.next();
             result
         } else {
@@ -595,30 +588,6 @@ impl<'a, F: Fn(&[u8]) -> Result<EncodedQuad>> Iterator for DecodingIndexIterator
     }
 }
 
-pub struct RocksString {
-    vec: DBVector,
-}
-
-impl Deref for RocksString {
-    type Target = str;
-
-    fn deref(&self) -> &str {
-        unsafe { str::from_utf8_unchecked(&self.vec) }
-    }
-}
-
-impl ToString for RocksString {
-    fn to_string(&self) -> String {
-        self.deref().to_owned()
-    }
-}
-
-impl From<RocksString> for String {
-    fn from(val: RocksString) -> String {
-        val.deref().to_owned()
-    }
-}
-
 #[test]
 fn repository() -> Result<()> {
     use crate::model::*;