[英]How to set statement timeout for query execution
In my web app some postgres sql queries take along time for execution. 在我的网络应用程序中,一些postgres sql查询需要时间来执行。 I want set statement timeout for only part of them.
我想只为其中一部分设置语句超时。
One part of queries must canceled by timeout, but other must work without any restriction. 查询的一部分必须通过超时取消,但其他部分必须无任何限制地工作。
In postgres exist statement_timeout function. 在postgres中存在statement_timeout函数。
How to wrap SqlAlchemy query with statement_timeout function? 如何用statement_timeout函数包装SqlAlchemy查询?
Like this: 像这样:
SET statement_timeout TO 1000; -- timeout for one second
<sqlalchemy generated query>;
RESET statement_timeout; -- reset
Perfect way for me set timeout for query like this: 对我来说完美的方式设置查询超时,如下所示:
users = session.query(User).timeout(0.5).all()
SqlAlchemy must: 1) set statement timeout 2) execute query and return result 3) reset statement timeout for current session SqlAlchemy必须:1)设置语句超时2)执行查询并返回结果3)当前会话的重置语句超时
May be other way to set timeout for query execution? 可能是为查询执行设置超时的其他方法?
UPDATE 1. My solution 更新1.我的解决方案
My solution is a custom connection proxy (tested with psycopg2==2.4 and SQLAlchemy==0.6.6): 我的解决方案是自定义连接代理(使用psycopg2 == 2.4和SQLAlchemy == 0.6.6测试):
from sqlalchemy.interfaces import ConnectionProxy
class TimeOutProxy(ConnectionProxy):
def cursor_execute(self, execute, cursor, statement, parameters, context, executemany):
timeout = context.execution_options.get('timeout', None)
if timeout:
c = cursor._parent.cursor()
c.execute('SET statement_timeout TO %d;' % int(timeout * 1000))
c.close()
return execute(cursor, statement, parameters, context)
engine = create_engine(URL, proxy=TimeOutProxy(), pool_size=1, max_overflow=0)
This solution without reseting statement_timeout, because each SqlAlchemy query executed in isolated transaction and statement_timeout defined inside current transaction. 此解决方案无需重置statement_timeout,因为每个SqlAlchemy查询都在隔离事务中执行,而statement_timeout在当前事务中定义。
Usage example (timeout pаram in seconds): 用法示例(以秒为单位的超时参数):
Session.query(Author).execution_options(timeout=0.001).all()
Session.bind.execute(text('select * from author;') \
.execution_options(timeout=0.001)) \
.fetchall()
You should look at the extensions provided with SQLAlchemy <= 0.6: 您应该查看SQLAlchemy <= 0.6提供的扩展:
http://www.sqlalchemy.org/docs/06/orm/interfaces.html http://www.sqlalchemy.org/docs/06/orm/interfaces.html
There are hooks where you could stick in your code for individual operations. 有一些钩子,你可以在你的代码中坚持个人操作。
SQLAlchemy 0.7+ now has an event system...there might be something similar. SQLAlchemy 0.7+现在有一个事件系统......可能有类似的东西。 See
看到
http://www.sqlalchemy.org/docs/core/events.html http://www.sqlalchemy.org/docs/core/events.html
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