virtual ~RemoteExecutor() = default;

virtual ResultSet execute(const char* backend_name, sql_parser::StringRef sql) = 0;

virtual DmlResult execute_dml(const char* backend_name, sql_parser::StringRef sql) {

(void)backend_name;

(void)sql;

DmlResult r;

r.error_message = "execute_dml not implemented";

return r;

}

// Returns true only when this executor can safely run distributed 2PC

// without pinned sessions. This is valid for executors that keep one

// durable physical connection per backend for the full lifetime of the

// executor. Pooled executors must return false and rely on

// checkout_session() instead.

virtual bool allows_unpinned_distributed_2pc() const { return false; }

// Check out a pinned session for `backend_name`. The returned session

// owns a specific physical connection for its lifetime; every call on

// it goes to that same connection. On destruction the connection is

// returned to the pool (or closed if the session was poisoned).

//

// REQUIRED for correct pooled 2PC behavior: MySQL XA and PostgreSQL

// PREPARE TRANSACTION both need the transaction's DML and PREPARE to

// share a session. Executors may return nullptr only if they also

// override allows_unpinned_distributed_2pc() to declare the legacy

// single-connection fallback safe for their execution model.

virtual std::unique_ptr<RemoteSession> checkout_session(const char* backend_name) {

(void)backend_name;

return nullptr;

}