SQLAlchemy是否支持某种缓存机制,以便如果我重复运行相同的查询,它将从缓存中返回响应,而不是查询数据库?这个缓存是否在更新数据库时自动清除?
或者,在一个CherryPy + SQLAlchemy设置中实现这个功能的最佳方法是什么?
SQLAlchemy是否支持某种缓存机制,以便如果我重复运行相同的查询,它将从缓存中返回响应,而不是查询数据库?这个缓存是否在更新数据库时自动清除?
或者,在一个CherryPy + SQLAlchemy设置中实现这个功能的最佳方法是什么?
dogpile
缓存: http://docs.sqlalchemy.org/en/latest/orm/examples.html#module-examples.dogpile_caching。SQLAlchemy支持两种类型的缓存:
缓存结果集,以便重复运行相同的查询时使用缓存而不是数据库。它使用dogpile
,支持许多不同的后端,包括memcached
、redis
和基本的平面文件。
文档在这里:http://docs.sqlalchemy.org/en/latest/orm/examples.html#module-examples.dogpile_caching
缓存query
对象,以便Python解释器不必每次手动重新组装查询字符串。这些查询称为baked queries
,缓存称为baked
。它基本上缓存了所有sqlalchemy
在访问数据库之前执行的操作——它不会减少数据库调用次数。初步的基准测试显示,query
生成时间的加速最高可达40%,代价是代码冗长略微增加。
文档在这里:http://docs.sqlalchemy.org/en/latest/orm/extensions/baked.html
虽然不是回答你的第二个问题,但该链接中的评论表明SQLAlchemy不支持缓存:http://spyced.blogspot.com/2007/01/why-sqlalchemy-impresses-me.html
Raven说:
Does SQLAlchemy do any kind of internal caching?
For example, if you ask for the same data twice (or an obvious subset
of the initially requested data) will the database be hit once or twice?
I recently wrote a caching database abstraction layer for an
application and (while fun) it was a fair bit of work to get it to a
minimally functional state. If SQLAlchemy did that I would seriously
consider jumping on the bandwagon.
I've found things in the docs that imply something like this might be
going on, but nothing explicit.
4:36 PM
Jonathan Ellis 说:... No; the author of SA [rightly, IMO] considers caching a separate concern.
What you saw in the docs is probably the SA identity map, which makes it so
if you load an instance in two different places, they will refer
to the same object. But the database will still be queried twice, so it is
not a cache in the sense you mean.
或者使用应用程序级别的缓存,通过弱引用字典 (weakref.WeakValueDictionary),在这里可以看到一个示例:http://www.sqlalchemy.org/trac/wiki/UsageRecipes/UniqueObject