Prevent needless key/value copies in database methods

Signed-off-by: Victor Porof <victor.porof@gmail.com>

Cargo.toml

@@ -16,7 +16,7 @@ exclude = ["/tests/envs/*"]
 [features]
 default = ["with-safe-mode"]
 backtrace = ["failure/backtrace", "failure/std"]
-with-safe-mode = ["id-arena", "log", "serde/derive", "serde/rc"]
+with-safe-mode = ["hashbrown/serde", "id-arena", "log", "serde/derive", "serde/rc"]
 with-asan = ["lmdb-rkv/with-asan"]
 with-fuzzer = ["lmdb-rkv/with-fuzzer"]
 with-fuzzer-no-link = ["lmdb-rkv/with-fuzzer-no-link"]
@@ -26,6 +26,7 @@ arrayref = "0.3"
 bincode = "1.0"
 bitflags = "1"
 byteorder = "1"
+hashbrown = { version = "0.6", optional = true }
 id-arena = { version = "2.2", optional = true }
 lazy_static = "1.0"
 lmdb-rkv = "0.12.3"

src/backend/impl_safe/database.rs

@@ -8,12 +8,11 @@
 // CONDITIONS OF ANY KIND, either express or implied. See the License for the
 // specific language governing permissions and limitations under the License.
 
-use std::collections::{
-    BTreeSet,
-    HashMap,
-};
+use std::collections::BTreeSet;
 use std::sync::Arc;
 
+use hashbrown::hash_map::RawEntryMut;
+use hashbrown::HashMap;
 use id_arena::Id;
 use serde_derive::{
     Deserialize,
@@ -75,35 +74,49 @@ impl Snapshot {
 
     pub(crate) fn put_one(&mut self, key: &[u8], value: &[u8]) {
         let map = Arc::make_mut(&mut self.map);
-        let values = map.entry(Box::from(key)).or_insert_with(BTreeSet::new);
-        values.clear();
+        let entry = map.raw_entry_mut().from_key(key);
+        let (_, values) = entry.and_modify(|_, v| v.clear()).or_insert_with(|| (Box::from(key), BTreeSet::new()));
         values.insert(Box::from(value));
     }
 
     pub(crate) fn put_dup(&mut self, key: &[u8], value: &[u8]) {
         let map = Arc::make_mut(&mut self.map);
-        let values = map.entry(Box::from(key)).or_insert_with(BTreeSet::new);
+        let entry = map.raw_entry_mut().from_key(key);
+        let (_, values) = entry.or_insert_with(|| (Box::from(key), BTreeSet::new()));
         values.insert(Box::from(value));
     }
 
     pub(crate) fn del_exact(&mut self, key: &[u8], value: &[u8]) -> Option<()> {
         let map = Arc::make_mut(&mut self.map);
-        let values = map.entry(Box::from(key)).or_insert_with(BTreeSet::new);
-        let was_removed = values.remove(value);
-        Some(()).filter(|_| was_removed)
+        let entry = map.raw_entry_mut().from_key(key);
+
+        match entry {
+            RawEntryMut::Vacant(_) => None,
+            RawEntryMut::Occupied(mut entry) => {
+                let values = entry.get_mut();
+                let was_removed = values.remove(value);
+                Some(()).filter(|_| was_removed)
+            },
+        }
     }
 
     pub(crate) fn del_all(&mut self, key: &[u8]) -> Option<()> {
         let map = Arc::make_mut(&mut self.map);
-        let values = map.entry(Box::from(key)).or_insert_with(BTreeSet::new);
-        let was_empty = values.is_empty();
-        values.clear();
-        Some(()).filter(|_| !was_empty)
+        let entry = map.raw_entry_mut().from_key(key);
+
+        match entry {
+            RawEntryMut::Vacant(_) => None,
+            RawEntryMut::Occupied(mut entry) => {
+                let values = entry.get_mut();
+                let was_empty = values.is_empty();
+                values.clear();
+                Some(()).filter(|_| !was_empty)
+            },
+        }
     }
 
     pub(crate) fn clear(&mut self) {
-        let map = Arc::make_mut(&mut self.map);
-        map.clear();
+        self.map = Default::default();
     }
 
     pub(crate) fn iter(&self) -> impl Iterator<Item = (&[u8], &[u8])> {