add benchmark for vec cache

test storage::sqlite::bench::bench_hash_cache ... bench:         399 ns/iter (+/- 27)
test storage::sqlite::bench::bench_no_cache   ... bench:       4,854 ns/iter (+/- 499)
test storage::sqlite::bench::bench_vec_cache  ... bench:           0 ns/iter (+/- 0)

rslib/Cargo.toml

@@ -5,6 +5,9 @@ edition = "2018"
 authors = ["Ankitects Pty Ltd and contributors"]
 license = "AGPL-3.0-or-later"
 
+[features]
+unstable = []
+
 [dependencies]
 nom = "5.0.1"
 failure = "0.1.7"

rslib/src/lib.rs

@@ -2,6 +2,7 @@
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
 #![deny(unused_must_use)]
+#![cfg_attr(feature = "unstable", feature(test))]
 
 mod backend_proto;
 

rslib/src/storage/sqlite.rs

@@ -379,3 +379,42 @@ impl StorageContext<'_> {
         Ok(*self.timing_today.as_ref().unwrap())
     }
 }
+
+#[cfg(all(feature = "unstable", test))]
+mod bench {
+    extern crate test;
+    use super::{CachedStatementKind, SqliteStorage};
+    use std::path::Path;
+    use test::Bencher;
+
+    const SQL: &str = "insert or replace into cards
+    (id, nid, did, ord, mod, usn, type, queue, due, ivl, factor,
+    reps, lapses, left, odue, odid, flags, data)
+    values
+    (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
+
+    #[bench]
+    fn bench_no_cache(b: &mut Bencher) {
+        let storage = SqliteStorage::open_or_create(Path::new(":memory:")).unwrap();
+        b.iter(|| storage.db.prepare(SQL).unwrap());
+    }
+
+    #[bench]
+    fn bench_hash_cache(b: &mut Bencher) {
+        let storage = SqliteStorage::open_or_create(Path::new(":memory:")).unwrap();
+        b.iter(|| storage.db.prepare_cached(SQL).unwrap());
+    }
+
+    #[bench]
+    fn bench_vec_cache(b: &mut Bencher) {
+        let storage = SqliteStorage::open_or_create(Path::new(":memory:")).unwrap();
+        let mut ctx = storage.context(false);
+        b.iter(|| {
+            ctx.with_cached_stmt(CachedStatementKind::GetCard, SQL, |_stmt| {
+                test::black_box(_stmt);
+                Ok(())
+            })
+            .unwrap()
+        });
+    }
+}