void FetchOperation::killRunningQuery()

in squangle/mysql_client/Operation.cpp [1499:1540]

• 28 lines of code
• 3 McCabe index (conditional complexity)

void FetchOperation::killRunningQuery() {
  /*
   * Send kill command to terminate the current operation on the DB
   * Note that we use KILL <processlist_id> to kill the entire connection
   * In the event the DB is behind a proxy this will kill the persistent
   * connection the proxy is using, so ConnectionOptions::killQueryOnTimeout_
   * should always be false when accessing the DB through a proxy
   *
   * Note that there is a risk of a race condition in the event that a proxy
   * is used and a query from this client times out, then the query completes
   * almost immediately after the timeout and a proxy gives the persistent
   * connection to another client which begins a query on that connection
   * before this client is able to send the KILL query on a separate
   * proxy->db connection which then terminates the OTHER client's query
   */
  auto thread_id = conn()->mysqlThreadId();
  auto host = conn()->host();
  auto port = conn()->port();
  auto conn_op = client()
                     ->beginConnection(*conn()->getKey())
                     ->setConnectionOptions(conn()->getConnectionOptions());
  conn_op->setCallback([thread_id, host, port](ConnectOperation& conn_op) {
    if (conn_op.ok()) {
      auto op = Connection::beginQuery(
          conn_op.releaseConnection(), "KILL %d", thread_id);
      op->setCallback([thread_id, host, port](
                          QueryOperation& /* unused */,
                          QueryResult* /* unused */,
                          QueryCallbackReason reason) {
        if (reason == QueryCallbackReason::Failure) {
          LOG(WARNING) << folly::format(
              "Failed to kill query in thread {} on {}:{}",
              thread_id,
              host,
              port);
        }
      });
      op->run();
    }
  });
  conn_op->run();
}