Fix PostgreSQL memory leak when statement cache is disabled

sqlx-postgres/src/connection/executor.rs

@@ -28,7 +28,9 @@ async fn prepare(
     persistent: bool,
     resolve_column_origin: bool,
 ) -> Result<(StatementId, Arc<PgStatementMetadata>), Error> {
-    let id = if persistent {
+    // if cache is disabled, persistent statements get an id but are never evicted
+    // which causes a memory leak
+    let id = if persistent && conn.inner.cache_statement.is_enabled() {
         let id = conn.inner.next_statement_id;
         conn.inner.next_statement_id = id.next();
         id

tests/postgres/postgres.rs

@@ -845,6 +845,32 @@ async fn it_closes_statements_when_not_persistent_issue_3850() -> anyhow::Result
     Ok(())
 }
 
+#[sqlx_macros::test]
+async fn it_closes_statements_when_caching_is_disabled_issue_4328() -> anyhow::Result<()> {
+    sqlx_test::setup_if_needed();
+
+    let mut options: PgConnectOptions = env::var("DATABASE_URL")?.parse().unwrap();
+
+    options = options.statement_cache_capacity(0);
+
+    let mut conn = PgConnection::connect_with(&options).await?;
+
+    let _row = sqlx::query("SELECT $1 AS val")
+        .bind(Oid(1))
+        .fetch_one(&mut conn)
+        .await?;
+
+    let row = sqlx::query("SELECT count(*) AS num_prepared_statements FROM pg_prepared_statements")
+        .persistent(false)
+        .fetch_one(&mut conn)
+        .await?;
+
+    let n: i64 = row.get("num_prepared_statements");
+    assert_eq!(0, n, "no prepared statements should be open");
+
+    Ok(())
+}
+
 #[sqlx_macros::test]
 async fn it_sets_application_name() -> anyhow::Result<()> {
     sqlx_test::setup_if_needed();