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POasynchronous call with Tornado and pyodbc
 

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    <p>I want to implement a web service based on tornado which can provide the database query service for users. I used the pyodbc module to connect to database and do the query. In practice, I found that printing the query result would take a long time. That is to say, if I used the following code to print the query result</p> <pre><code>while 1: data = cursor.fetchone() if not data: break self.write(data + '\n') self.flush() </code></pre> <p>and the sql command is something like</p> <pre><code>select * from &lt;a large dummy table&gt; </code></pre> <p>tornado would not print the query result until the loop is over. And it takes a long time.</p> <p>I wanna make use of tornado's non-blocking asynchronous feature to make other users also be able to use the web service even though the loop for printing the current user's query request is not finished yet.</p> <p>So I write something like:</p> <pre><code>@tornado.web.asynchronous def get(self): try: cnxn = pyodbc.connect(self.server, self.driver, self.table, self.uid, self.pwd) except Exception, e: print e return try: self.cur = cnxn.execute(self.sql) except Exception, e: print e return self.wait_for_query(callback=self.async_callback(self.on_finish)) def wait_for_query(self, callback): while 1: data = self.cur.fetchone() if not data: break self.write(data) self.flush() callback() def on_finish(self): self.finish() </code></pre> <p>I read this post: <a href="https://stackoverflow.com/questions/2317501/asynchronous-comet-query-with-tornado-and-prototype">Asynchronous COMET query with Tornado and Prototype</a> and knew my solution wouldn't work. But I certainly cannot use add_timeout, 'cause there is no way for me to figure out how long an iteration would last. So how can I work through this to achieve my goal? </p>
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