feat(backup): support table filters and MySQL compatibility

crates/dbx-core/src/query.rs

@@ -2918,14 +2918,26 @@ fn postgres_transaction_begin_sql(consistent_snapshot: bool) -> &'static str {
     }
 }
 
-fn mysql_transaction_begin_sql(consistent_snapshot: bool) -> &'static str {
+fn mysql_transaction_begin_sql_candidates(consistent_snapshot: bool) -> &'static [&'static str] {
     if consistent_snapshot {
-        "START TRANSACTION WITH CONSISTENT SNAPSHOT, READ ONLY"
+        &[
+            "START TRANSACTION WITH CONSISTENT SNAPSHOT, READ ONLY",
+            "START TRANSACTION WITH CONSISTENT SNAPSHOT",
+            "START TRANSACTION",
+        ]
     } else {
-        "START TRANSACTION"
+        &["START TRANSACTION"]
     }
 }
 
+fn mysql_transaction_isolation_sql(consistent_snapshot: bool) -> Option<&'static str> {
+    consistent_snapshot.then_some("SET TRANSACTION ISOLATION LEVEL REPEATABLE READ")
+}
+
+fn mysql_error_is_syntax_error(error: &mysql_async::Error) -> bool {
+    matches!(error, mysql_async::Error::Server(server_error) if server_error.code == 1064)
+}
+
 async fn begin_transaction_session(
     state: &AppState,
     connection_id: &str,
@@ -2968,8 +2980,25 @@ async fn begin_transaction_session(
         }
         TxnPoolHandle::Mysql(mysql_pool) => {
             let mut conn = mysql_pool.get_conn().await.map_err(|e| format!("Failed to get MySQL connection: {e}"))?;
-            let begin_sql = mysql_transaction_begin_sql(consistent_snapshot);
-            conn.query_drop(begin_sql).await.map_err(|e| format!("START TRANSACTION failed: {e}"))?;
+            if let Some(isolation_sql) = mysql_transaction_isolation_sql(consistent_snapshot) {
+                conn.query_drop(isolation_sql).await.map_err(|e| format!("SET TRANSACTION failed: {e}"))?;
+            }
+            let mut syntax_errors = Vec::new();
+            for begin_sql in mysql_transaction_begin_sql_candidates(consistent_snapshot) {
+                match conn.query_drop(*begin_sql).await {
+                    Ok(()) => {
+                        syntax_errors.clear();
+                        break;
+                    }
+                    Err(error) if mysql_error_is_syntax_error(&error) => {
+                        syntax_errors.push(format!("{begin_sql}: {error}"));
+                    }
+                    Err(error) => return Err(format!("START TRANSACTION failed: {error}")),
+                }
+            }
+            if !syntax_errors.is_empty() {
+                return Err(format!("START TRANSACTION failed for all compatible forms: {}", syntax_errors.join("; ")));
+            }
             TxnConnection::Mysql(conn)
         }
     };
@@ -4956,8 +4985,35 @@ mod tests {
     }
 
     #[test]
-    fn database_backup_transactions_request_consistent_read_only_snapshots() {
+    fn database_backup_transactions_request_consistent_snapshots() {
         assert_eq!(postgres_transaction_begin_sql(true), "BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ READ ONLY");
-        assert_eq!(mysql_transaction_begin_sql(true), "START TRANSACTION WITH CONSISTENT SNAPSHOT, READ ONLY");
+        assert_eq!(mysql_transaction_isolation_sql(true), Some("SET TRANSACTION ISOLATION LEVEL REPEATABLE READ"));
+        assert_eq!(
+            mysql_transaction_begin_sql_candidates(true),
+            [
+                "START TRANSACTION WITH CONSISTENT SNAPSHOT, READ ONLY",
+                "START TRANSACTION WITH CONSISTENT SNAPSHOT",
+                "START TRANSACTION",
+            ]
+        );
+        assert_eq!(mysql_transaction_isolation_sql(false), None);
+        assert_eq!(mysql_transaction_begin_sql_candidates(false), ["START TRANSACTION"]);
+    }
+
+    #[test]
+    fn mysql_backup_transaction_only_falls_back_for_syntax_errors() {
+        let syntax_error = mysql_async::Error::Server(mysql_async::ServerError {
+            code: 1064,
+            message: "unsupported transaction characteristic".to_string(),
+            state: "42000".to_string(),
+        });
+        let permission_error = mysql_async::Error::Server(mysql_async::ServerError {
+            code: 1044,
+            message: "access denied".to_string(),
+            state: "42000".to_string(),
+        });
+
+        assert!(mysql_error_is_syntax_error(&syntax_error));
+        assert!(!mysql_error_is_syntax_error(&permission_error));
     }
 }