Try reusing memory

Fix #10

Author: pickfire

src/bin/basic_batched.rs

@@ -46,36 +46,36 @@ fn faker(tx: &Transaction, count: i64) {
 
     let mut stmt_with_area = tx.prepare_cached(st1.as_str()).unwrap();
     let mut stmt = tx.prepare_cached(st2.as_str()).unwrap();
+    let mut params_with_area = Vec::with_capacity(min_batch_size as usize);
+    let mut param_values: Vec<&dyn ToSql> = Vec::with_capacity(min_batch_size as usize * 3);
     for _ in 0..(count / min_batch_size) {
         let with_area = common::get_random_bool();
         let age = common::get_random_age();
         let is_active = common::get_random_active();
-        let mut param_values: Vec<_> = Vec::new();
         if with_area {
-            // lets prepare the batch
-            let mut vector = Vec::<(String, i8, i8)>::new();
             for _ in 0..min_batch_size {
                 let area_code = common::get_random_area_code();
-                vector.push((area_code, age, is_active));
+                params_with_area.push((area_code,));
             }
-            for batch in vector.iter() {
-                param_values.push(&batch.0 as &dyn ToSql);
-                param_values.push(&batch.1 as &dyn ToSql);
-                param_values.push(&batch.2 as &dyn ToSql);
+            for params in &params_with_area {
+                // Safety: extend lifetime of params as it will be cleared at the end of the loop
+                // to reuse memory
+                param_values.push(unsafe { std::mem::transmute(&params.0 as &dyn ToSql) });
+                param_values.push(unsafe { std::mem::transmute(&age as &dyn ToSql) });
+                param_values.push(unsafe { std::mem::transmute(&is_active as &dyn ToSql) });
             }
             stmt_with_area.execute(&*param_values).unwrap();
+            params_with_area.clear();
         } else {
-            // lets prepare the batch
-            let mut vector = Vec::<(i8, i8)>::new();
             for _ in 0..min_batch_size {
-                vector.push((age, is_active));
-            }
-            for batch in vector.iter() {
-                param_values.push(&batch.0 as &dyn ToSql);
-                param_values.push(&batch.1 as &dyn ToSql);
+                // Safety: extend lifetime of params as it will be cleared at the end of the loop
+                // to reuse memory
+                param_values.push(unsafe { std::mem::transmute(&age as &dyn ToSql) });
+                param_values.push(unsafe { std::mem::transmute(&is_active as &dyn ToSql) });
             }
             stmt.execute(&*param_values).unwrap();
         }
+        param_values.clear();
     }
 }