LRU caching for SQLite

sqlx-core/src/common/statement_cache.rs

@@ -3,11 +3,11 @@ use lru_cache::LruCache;
 /// A cache for prepared statements. When full, the least recently used
 /// statement gets removed.
 #[derive(Debug)]
-pub struct StatementCache {
-    inner: LruCache<String, u32>,
+pub struct StatementCache<T> {
+    inner: LruCache<String, T>,
 }
 
-impl StatementCache {
+impl<T> StatementCache<T> {
     /// Create a new cache with the given capacity.
     pub fn new(capacity: usize) -> Self {
         Self {
@@ -17,19 +17,19 @@ impl StatementCache {
 
     /// Returns a mutable reference to the value corresponding to the given key
     /// in the cache, if any.
-    pub fn get_mut(&mut self, k: &str) -> Option<&mut u32> {
+    pub fn get_mut(&mut self, k: &str) -> Option<&mut T> {
         self.inner.get_mut(k)
     }
 
     /// Inserts a new statement to the cache, returning the least recently used
     /// statement id if the cache is full, or if inserting with an existing key,
     /// the replaced existing statement.
-    pub fn insert(&mut self, k: &str, v: u32) -> Option<u32> {
+    pub fn insert(&mut self, k: &str, v: T) -> Option<T> {
         let mut lru_item = None;
 
         if self.inner.capacity() == self.len() && !self.inner.contains_key(k) {
             lru_item = self.remove_lru();
-        } else if self.inner.contains_key(k) {
+        } else if self.contains_key(k) {
             lru_item = self.inner.remove(k);
         }
 
@@ -44,12 +44,17 @@ impl StatementCache {
     }
 
     /// Removes the least recently used item from the cache.
-    pub fn remove_lru(&mut self) -> Option<u32> {
+    pub fn remove_lru(&mut self) -> Option<T> {
         self.inner.remove_lru().map(|(_, v)| v)
     }
 
     /// Clear all cached statements from the cache.
     pub fn clear(&mut self) {
         self.inner.clear();
     }
+
+    /// True if cache has a value for the given key.
+    pub fn contains_key(&mut self, k: &str) -> bool {
+        self.inner.contains_key(k)
+    }
 }

sqlx-core/src/mysql/connection/mod.rs

@@ -37,7 +37,7 @@ pub struct MySqlConnection {
     pub(crate) stream: MySqlStream,
 
     // cache by query string to the statement id
-    cache_statement: StatementCache,
+    cache_statement: StatementCache<u32>,
 
     // working memory for the active row's column information
     // this allows us to re-use these allocations unless the user is persisting the

sqlx-core/src/postgres/connection/mod.rs

@@ -48,7 +48,7 @@ pub struct PgConnection {
     next_statement_id: u32,
 
     // cache statement by query string to the id and columns
-    cache_statement: StatementCache,
+    cache_statement: StatementCache<u32>,
 
     // cache user-defined types by id <-> info
     cache_type_info: HashMap<u32, PgTypeInfo>,