10

我只是在学习 Google App Engine，并试图找出一种管理我的数据库与 Google Cloud SQL 实例的连接的好方法（如果你没有使用过 GC-SQL，基本上，它是云中的 MySQL，有一些限制）。

我正在使用带有 webapp2 框架的 python (2.7) GAE 环境来处理请求。我知道常见问题解答说建议对每个请求都建立与数据库的新连接，但我不知道关闭连接的推荐方法是什么。每次我在开发过程中尝试删除表时，GC-SQL 挂起并且“显示进程列表”显示有一堆进程（可能是因为我没有关闭数据库）并且其中一个正在等待锁定（可能是试图删除表的过程）。这很烦人，迫使我重新启动 GC-SQL 实例（我想就像重新启动 mysql-server 服务）。我认为偶尔也会出现数据库故障，这与我并没有真正关闭数据库连接这一事实有关。

因此，例如，我是否应该在我的 webapp2.Requesthandler 子类实例上有一个析构函数来断开与数据库的连接？GAE 对象有时似乎会被缓存，所以这也是需要考虑的事情。我想我可以为每个查询连接/查询/断开连接，但这似乎不是最理想的。

我知道这是一个模糊的问题，但我希望在这方面玩过的人可以给我一些建议。

提前致谢！

更新： 我尝试使用 Shay 的答案作为起点，围绕需要光标的方法实现包装器。我收到 GAE 错误。这里有一个新的问题：App Engine 对 Google Cloud SQL 的连接限制是什么，以及如何最好地重用数据库连接？

4

4 回答 4

10

这是入门指南中 helloworld 示例应用程序的完整示例。它基于Shay Erlichmen和JJC的片段，但这个版本是线程安全的。

你可以像这样使用它：

  @with_db_cursor(do_commit = True)
  def get(self, cursor):
        cursor.execute('SELECT guestName, content, entryID FROM entries')

应用程序.yaml

application: helloworld
version: 1
runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: helloworld.app

你好世界.py

import cgi
import logging
import os
import threading
import webapp2

from google.appengine.api import rdbms

_INSTANCE_NAME = <name goes here>

def _db_connect():
  return rdbms.connect(instance=_INSTANCE_NAME, database='guestbook')

_mydata = threading.local()

def with_db_cursor(do_commit = False):
  """ Decorator for managing DB connection by wrapping around web calls.

  Stores connections and open cursor count in a threadlocal
  between calls.  Sets a cursor variable in the wrapped function. Optionally
  does a commit.  Closes the cursor when wrapped method returns, and closes
  the DB connection if there are no outstanding cursors.

  If the wrapped method has a keyword argument 'existing_cursor', whose value
  is non-False, this wrapper is bypassed, as it is assumed another cursor is
  already in force because of an alternate call stack.
  """
  def method_wrap(method):
    def wrap(self, *args, **kwargs):
      if kwargs.get('existing_cursor', False):
        # Bypass everything if method called with existing open cursor.
        return method(self, None, *args, **kwargs)

      if not hasattr(_mydata, 'conn') or not _mydata.conn:
        _mydata.conn = _db_connect()
        _mydata.ref = 0
        _mydata.commit = False

      conn = _mydata.conn
      _mydata.ref = _mydata.ref + 1

      try:
        cursor = conn.cursor()
        try:
          result = method(self, cursor, *args, **kwargs)
          if do_commit or _mydata.commit:
            _mydata.commit = False
            conn.commit()
          return result
        finally:
          cursor.close()
      finally:
        _mydata.ref = _mydata.ref - 1
        if _mydata.ref == 0:
          _mydata.conn = None
          logging.info('Closing conn')
          conn.close()
    return wrap
  return method_wrap


class MainPage(webapp2.RequestHandler):
  @with_db_cursor(do_commit = True)
  def get(self, cursor):
        cursor.execute('SELECT guestName, content, entryID FROM entries')
        self.response.out.write("""
          <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
          <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
            <head>
               <title>My Guestbook!</title>
            </head>
            <body>""")
        self.response.out.write("""
              <table style="border: 1px solid black">
                <tbody>
                  <tr>
                    <th width="35%" style="background-color: #CCFFCC; margin: 5px">Name</th>
                    <th style="background-color: #CCFFCC; margin: 5px">Message</th>
                    <th style="background-color: #CCFFCC; margin: 5px">ID</th>
                  </tr>""")
        for row in cursor.fetchall():
          self.response.out.write('<tr><td>')
          self.response.out.write(cgi.escape(row[0]))
          self.response.out.write('</td><td>')
          self.response.out.write(cgi.escape(row[1]))
          self.response.out.write('</td><td>')
          self.response.out.write(row[2])
          self.response.out.write('</td></tr>')

        self.response.out.write("""
          </tbody>
            </table>
              <br /> No more messages!
              <br /><strong>Sign the guestbook!</strong>
              <form action="/sign" method="post">
              <div>First Name: <input type="text" name="fname" style="border: 1px solid black"></div>
              <div>Message: <br /><textarea name="content" rows="3" cols="60"></textarea></div>
              <div><input type="submit" value="Sign Guestbook"></div>
            </form>
          </body>
        </html>""")

class Guestbook(webapp2.RequestHandler):
  @with_db_cursor(do_commit = True)
  def post(self, cursor):
    fname = self.request.get('fname')
    content = self.request.get('content')
    # Note that the only format string supported is %s
    cursor.execute('INSERT INTO entries (guestName, content) VALUES (%s, %s)', (fname, content))

    self.redirect("/")

app = webapp2.WSGIApplication(
    [('/', MainPage),
     ('/sign', Guestbook)],
    debug=True)
于 2012-05-03T20:10:29.560 回答
2

这是我的方法，它考虑了可能的例外情况。我在生产环境中使用这种方法并且效果很好：


def _create_connection(schema):

    if (os.getenv('SERVER_SOFTWARE') and
        os.getenv('SERVER_SOFTWARE').startswith('Google App Engine/')):
        socket = '/cloudsql/%s' % env.DB_INSTANCE_NAME
        return MySQLdb.connect(unix_socket=socket, user=env.DB_APP_USER,
                               passwd=env.DB_APP_PASS, db=schema)
    else:
        return MySQLdb.connect(host='127.0.0.1', port=3306,
                               user=env.DB_APP_USER, passwd=env.DB_APP_PASS,
                               db=schema)


def with_db(commit=False, schema=env.DB_SCHEMA_NAME):

    def method_wrap(method):
        @functools.wraps(method)
        def wrap(self, *args, **kwds):
            # If needed,a connection pool can be added here.
            connection = _create_connection(schema)

            try:
                cur = connection.cursor()
                self.cur = cur
                self.conn = connection

                result = method(self, *args, **kwds)

                if commit:
                    connection.commit()

            except OperationalError as e:

                logging.error('Operational error.\r\nSQL exception: {},\r\n'
                              'Last Query: {}'.format(e, cur._last_executed))

                if commit and connection.open:
                    connection.rollback()
                raise

            except MySQLError as e:

                try:
                    warns = self.conn.show_warnings()
                    error = self.conn.error()
                except:
                    warns = ""
                    error = ""

                logging.error('Try to rolling back transaction.\r\nSQL exception: {},\r\n'
                              'Last Query: {},\r\nConn warn: {},\r\nError: {}'
                              .format(e, cur._last_executed, warns, error))


                if commit and connection.open:
                    connection.rollback()
                raise

            except Exception as e:
                logging.error('Try to rolling back transaction. Non SQL exception: {0}'.format(e))

                if commit and connection.open:
                    connection.rollback()
                raise

            finally:
                connection.close()

            return result
        return wrap
    return method_wrap

你可以像这样使用它：


@with_db(commit=True)
def update_user_phone(self, user, phone):
    self.cur.execute(_SQL_UPDATE_USER_PHONE, (phone, user.id))

    # add or replace existing user to cache
    user.phone = phone
    self._update_user_cache(user)
于 2014-09-30T18:16:25.650 回答
2

我不熟悉 Google Cloud SQL，但您不能使用 WSGI 中间件来打开和关闭连接吗？

于 2012-04-15T04:21:02.137 回答
2

我写了一个装饰器来处理 SQL 连接，请随意火焰 :)

# Here is how you use the decorator from below
# the open, commit, and close is done by the decorator 
@need_cursor(do_commit = True)
def get(self, cursor, request): # cursor param is added by the decorator
    execute_sql(cursor, sql)

def need_cursor(do_commit = False):
    def method_wrap(method):
        def wrap(*args, **kwargs):
            conn = os.environ.get("__data_conn")

            # Recycling connection for the current request
            # For some reason threading.local() didn't worked
            # and yes os.environ suppose to be thread safe 
            if not conn:                
                conn = create_connection() # You need to implement this
                os.environ["__data_conn"] = conn
                os.environ["__data_conn_ref"] = 1
            else:
                os.environ["__data_conn_ref"] = 
                    os.environ["__data_conn_ref"] + 1

            try:
                cursor = conn.cursor()
                try:
                    result = method(cursor, *args, **kwargs)

                    if do_commit or os.environ.get("__data_conn_commit"):
                        os.environ["__data_conn_commit"] = False
                        conn.commit()

                    return result                    
                finally:
                    cursor.close()                
            finally:
                os.environ["__data_conn_ref"] = 
                    os.environ["__data_conn_ref"] - 1
                if os.environ["__data_conn_ref"] == 0:
                    os.environ["__data_conn"] = None
                    conn.close()        

        return wrap

    return method_wrap
于 2012-04-15T14:00:17.803 回答