【Patroni源码阅读】Postgresql 启动PG

start.py

class Postgresql(object):
    def start(self, timeout=None, task=None, block_callbacks=False, role=None):
        """Start PostgreSQL

        Waits for postmaster to open ports or terminate so pg_isready can be used to check startup completion
        or failure.

        :returns: True if start was initiated and postmaster ports are open, False if start failed"""
        # make sure we close all connections established against
        # the former node, otherwise, we might get a stalled one
        # after kill -9, which would report incorrect data to
        # patroni.

        # 关闭之前打开的postgresql连接
        self._connection.close()

        # postgresql正在运行
        if self.is_running():
            logger.error('Cannot start PostgreSQL because one is already running.')
            self.set_state('starting')
            return True

        if not block_callbacks:
            self.__cb_pending = ACTION_ON_START

        self.set_role(role or self.get_postgres_role_from_data_directory())

        self.set_state('starting')
        self._pending_restart = False

        try:
            if not self._major_version:
                self.configure_server_parameters()
            configuration = self.config.effective_configuration
        except Exception:
            return None

        self.config.check_directories()
        self.config.write_postgresql_conf(configuration)
        self.config.resolve_connection_addresses()
        self.config.replace_pg_hba()
        self.config.replace_pg_ident()

        options = ['--{0}={1}'.format(p, configuration[p]) for p in self.config.CMDLINE_OPTIONS
                   if p in configuration and p not in ('wal_keep_segments', 'wal_keep_size')]

        if self.cancellable.is_cancelled:
            return False

        with task or null_context():
            if task and task.is_cancelled:
                logger.info("PostgreSQL start cancelled.")
                return False

            self._postmaster_proc = PostmasterProcess.start(self.pgcommand('postgres'),
                                                            self._data_dir,
                                                            self.config.postgresql_conf,
                                                            options)

            if task:
                task.complete(self._postmaster_proc)

        start_timeout = timeout
        if not start_timeout:
            try:
                start_timeout = float(self.config.get('pg_ctl_timeout', 60))
            except ValueError:
                start_timeout = 60

        # 等待进程的端口打开
        if not self._postmaster_proc or not self.wait_for_port_open(self._postmaster_proc, start_timeout):
            return False

        # 检查启动是否完成，主要逻辑在 check_startup_state_changed()和pg_isready()接口中，原理是反复调用：pg_isready -U postgres -p 5432, 并且返回信息
        #         return_codes = {0: STATE_RUNNING,
        #                         1: STATE_REJECT,
        #                         2: STATE_NO_RESPONSE,
        #                         3: STATE_UNKNOWN}
        ret = self.wait_for_startup(start_timeout)
        if ret is not None:
            return ret # True启动成功
        elif timeout is not None:
            return False
        else:
            return None