*: skeleton of range query

src/bench.rs

@@ -765,6 +765,9 @@ fn bench_worker_regular(
                 Operation::Delete { key } => {
                     handle.delete(&key[..]);
                 }
+                Operation::Scan { key, n } => {
+                    let _ = handle.scan(&key[..], n);
+                }
             }
             let op_end = latency_tick();
             if let Some(ref mut l) = latency {

src/lib.rs

@@ -88,7 +88,8 @@ pub trait KVMapHandle {
     /// Removing a key if it exists.
     fn delete(&mut self, key: &[u8]);
 
-    // fn read_modify_write(&mut self, key: &[u8]);
+    /// Querying a range starting from the first key greater than or equal to the given key.
+    fn scan(&mut self, key: &[u8], n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)>;
 }
 
 /// A single operation that is applied to the key-value store.
@@ -104,6 +105,9 @@ pub enum Operation {
 
     /// Removing a key if it exists.
     Delete { key: Box<[u8]> },
+
+    /// Querying a range starting from the first key greater than or equal to the given key.
+    Scan { key: Box<[u8]>, n: usize },
 }
 
 /// A request sent by a client to a server.

src/server.rs

@@ -112,6 +112,9 @@ fn serve_requests_regular(
                 handle.delete(key);
                 assert!(write_response(&mut *writer, id, None).is_ok());
             }
+            Operation::Scan { .. } => {
+                todo!()
+            }
         }
     }
 }

src/stores/btreemap.rs

@@ -60,6 +60,11 @@ impl KVMapHandle for MutexBTreeMap {
     fn delete(&mut self, key: &[u8]) {
         self.0.lock().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        // technically iteration is supported but querying a specific range is not a stable feature
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {
@@ -102,6 +107,11 @@ impl KVMapHandle for RwLockBTreeMap {
     fn delete(&mut self, key: &[u8]) {
         self.0.write().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        // technically iteration is supported but querying a specific range is not a stable feature
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/chashmap.rs

@@ -45,6 +45,10 @@ impl KVMapHandle for CHashMap {
     fn delete(&mut self, key: &[u8]) {
         self.0.remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/contrie.rs

@@ -46,6 +46,10 @@ impl KVMapHandle for Contrie {
     fn delete(&mut self, key: &[u8]) {
         self.0.remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/dashmap.rs

@@ -46,6 +46,10 @@ impl KVMapHandle for DashMap {
     fn delete(&mut self, key: &[u8]) {
         self.0.remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/flurry.rs

@@ -46,6 +46,10 @@ impl KVMapHandle for Flurry {
     fn delete(&mut self, key: &[u8]) {
         self.0.pin().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/hashmap.rs

@@ -99,6 +99,10 @@ impl KVMapHandle for MutexHashMap {
         let sid = shard(key, self.nr_shards);
         self.shards[sid].lock().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {
@@ -161,6 +165,10 @@ impl KVMapHandle for RwLockHashMap {
         let sid = shard(key, self.nr_shards);
         self.shards[sid].write().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/null.rs

@@ -54,6 +54,10 @@ impl KVMapHandle for NullMap {
     }
 
     fn delete(&mut self, _key: &[u8]) {}
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        Vec::new()
+    }
 }
 
 inventory::submit! {

src/stores/papaya.rs

@@ -46,6 +46,10 @@ impl KVMapHandle for Papaya {
     fn delete(&mut self, key: &[u8]) {
         self.0.pin().remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/stores/rocksdb.rs

@@ -12,7 +12,7 @@
 
 use crate::stores::{BenchKVMap, Registry};
 use crate::*;
-use rocksdb::DB;
+use rocksdb::{Direction, IteratorMode, DB};
 use serde::Deserialize;
 
 #[derive(Deserialize)]
@@ -59,6 +59,22 @@ impl KVMapHandle for RocksDB {
     fn delete(&mut self, key: &[u8]) {
         assert!(self.db.delete(key).is_ok());
     }
+
+    fn scan(&mut self, key: &[u8], n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        let mut kv = Vec::with_capacity(n);
+        let iter = self
+            .db
+            .iterator(IteratorMode::From(key, Direction::Forward));
+        let mut i = 0;
+        for item in iter {
+            kv.push(item.unwrap());
+            i += 1;
+            if i == n {
+                break;
+            }
+        }
+        kv
+    }
 }
 
 inventory::submit! {

src/stores/scc.rs

@@ -49,6 +49,10 @@ impl KVMapHandle for SccHashMap {
     fn delete(&mut self, key: &[u8]) {
         self.0.remove(key);
     }
+
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
+        unimplemented!("Range query is not supported");
+    }
 }
 
 inventory::submit! {

src/workload.rs

@@ -758,7 +758,7 @@ mod tests {
                     dist.entry(key).and_modify(|c| *c += 1).or_insert(0);
                     get += 1;
                 }
-                Operation::Delete { .. } => {
+                Operation::Delete { .. } | Operation::Scan { .. } => {
                     unreachable!();
                 }
             }