feat(testing): implement template database cloning for MySQL

Add template database cloning optimization to avoid running migrations for
every test. When multiple tests use the same migrations, a template database
is created once and cloned for each test, significantly speeding up test runs.

Implementation details:
- Add migrations_hash() to compute SHA256 of migration checksums
- Add template_db_name() to generate template database names
- Extend TestContext with from_template field to track cloning
- Modify setup_test_db() to skip migrations when cloned from template
- MySQL: Use mysqldump/mysql for fast cloning with in-process fallback
- Add _sqlx_test_templates tracking table with GET_LOCK synchronization
- Add SQLX_TEST_NO_TEMPLATE env var to opt out of template cloning
- Add comprehensive tests for template functionality
- Add template tests to MySQL and MariaDB CI jobs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: CodingAnarchy

.github/workflows/sqlx.yml

@@ -371,6 +371,17 @@ jobs:
           SQLX_OFFLINE_DIR: .sqlx
           RUSTFLAGS: --cfg mysql_${{ matrix.mysql }}
 
+      # Run template database cloning tests
+      - run: >
+          cargo test
+          --test mysql-template
+          --no-default-features
+          --features any,mysql,macros,migrate,_unstable-all-types,runtime-${{ matrix.runtime }},tls-${{ matrix.tls }}
+        env:
+          DATABASE_URL: mysql://root:password@localhost:3306/sqlx?ssl-mode=disabled
+          SQLX_OFFLINE_DIR: .sqlx
+          RUSTFLAGS: --cfg mysql_${{ matrix.mysql }}
+
       # MySQL 5.7 supports TLS but not TLSv1.3 as required by RusTLS.
       - if: ${{ !(matrix.mysql == '5_7' && matrix.tls == 'rustls') }}
         run: >
@@ -472,6 +483,17 @@ jobs:
           SQLX_OFFLINE_DIR: .sqlx
           RUSTFLAGS: --cfg mariadb="${{ matrix.mariadb }}"
 
+      # Run template database cloning tests
+      - run: >
+          cargo test
+          --test mysql-template
+          --no-default-features
+          --features any,mysql,macros,migrate,_unstable-all-types,runtime-${{ matrix.runtime }},tls-${{ matrix.tls }}
+        env:
+          DATABASE_URL: mysql://root:password@localhost:3306/sqlx
+          SQLX_OFFLINE_DIR: .sqlx
+          RUSTFLAGS: --cfg mariadb="${{ matrix.mariadb }}"
+
       # Remove test artifacts
       - run: cargo clean -p sqlx
 

Cargo.toml

@@ -391,6 +391,11 @@ name = "mysql-test-attr"
 path = "tests/mysql/test-attr.rs"
 required-features = ["mysql", "macros", "migrate"]
 
+[[test]]
+name = "mysql-template"
+path = "tests/mysql/template.rs"
+required-features = ["mysql", "macros", "migrate"]
+
 [[test]]
 name = "mysql-migrate"
 path = "tests/mysql/migrate.rs"

sqlx-core/src/testing/mod.rs

@@ -1,9 +1,12 @@
 use std::future::Future;
 use std::time::Duration;
 
-use base64::{engine::general_purpose::URL_SAFE, Engine as _};
+use base64::{
+    engine::general_purpose::{URL_SAFE, URL_SAFE_NO_PAD},
+    Engine as _,
+};
 pub use fixtures::FixtureSnapshot;
-use sha2::{Digest, Sha512};
+use sha2::{Digest, Sha256, Sha512};
 
 use crate::connection::{ConnectOptions, Connection};
 use crate::database::Database;
@@ -14,6 +17,35 @@ use crate::pool::{Pool, PoolConnection, PoolOptions};
 
 mod fixtures;
 
+/// Compute a combined hash of all migrations for template invalidation.
+///
+/// This hash is used to name template databases. When migrations change,
+/// a new hash is generated, resulting in a new template being created.
+pub fn migrations_hash(migrator: &Migrator) -> String {
+    let mut hasher = Sha256::new();
+
+    for migration in migrator.iter() {
+        // Include version, type, and checksum in the hash
+        hasher.update(migration.version.to_le_bytes());
+        hasher.update([migration.migration_type as u8]);
+        hasher.update(&*migration.checksum);
+    }
+
+    let hash = hasher.finalize();
+    // Use first 16 bytes (128 bits) for a reasonably short but unique name
+    URL_SAFE_NO_PAD.encode(&hash[..16])
+}
+
+/// Generate a template database name from a migrations hash.
+///
+/// Template names follow the pattern `_sqlx_template_<hash>` and are kept
+/// under 63 characters to respect database identifier limits.
+pub fn template_db_name(migrations_hash: &str) -> String {
+    // Replace any characters that might cause issues in database names
+    let safe_hash = migrations_hash.replace(['-', '+', '/'], "_");
+    format!("_sqlx_template_{}", safe_hash)
+}
+
 pub trait TestSupport: Database {
     /// Get parameters to construct a `Pool` suitable for testing.
     ///
@@ -82,6 +114,9 @@ pub struct TestContext<DB: Database> {
     pub pool_opts: PoolOptions<DB>,
     pub connect_opts: <DB::Connection as Connection>::Options,
     pub db_name: String,
+    /// Whether this test database was created from a template.
+    /// When true, migrations have already been applied and should be skipped.
+    pub from_template: bool,
 }
 
 impl<DB, Fut> TestFn for fn(Pool<DB>) -> Fut
@@ -226,7 +261,7 @@ where
             .await
             .expect("failed to connect to setup test database");
 
-        setup_test_db::<DB>(&test_context.connect_opts, &args).await;
+        setup_test_db::<DB>(&test_context.connect_opts, &args, test_context.from_template).await;
 
         let res = test_fn(test_context.pool_opts, test_context.connect_opts).await;
 
@@ -246,6 +281,7 @@ where
 async fn setup_test_db<DB: Database>(
     copts: &<DB::Connection as Connection>::Options,
     args: &TestArgs,
+    from_template: bool,
 ) where
     DB::Connection: Migrate + Sized,
     for<'c> &'c mut DB::Connection: Executor<'c, Database = DB>,
@@ -255,11 +291,15 @@ async fn setup_test_db<DB: Database>(
         .await
         .expect("failed to connect to test database");
 
-    if let Some(migrator) = args.migrator {
-        migrator
-            .run_direct(None, &mut conn)
-            .await
-            .expect("failed to apply migrations");
+    // Skip migrations if the database was cloned from a template
+    // (migrations were already applied to the template)
+    if !from_template {
+        if let Some(migrator) = args.migrator {
+            migrator
+                .run_direct(None, &mut conn)
+                .await
+                .expect("failed to apply migrations");
+        }
     }
 
     for fixture in args.fixtures {