还有其他的解决方案如cookie会话仓库(会话长度有限，不能在会话中存放敏感数据)，memcached(无法持久化+难以实现高可用性方案)。
There are other possible solutions like cookie session store (session size is limited, no sensible data in sessions), memcached (too much RAM when you have many sessions + no persistence).
这对我们来说是一项艰巨的集成任务，而且曝露了不少难以解决的微妙问题，比如异常处理、并发性、安全性、以及持久性上下文管理。
This was a difficult integration task for us, and exposed several subtle issues that were difficult to address like exception handling, concurrency, security, and persistence context management.
两冲程汽油动力的工具的环境污染和噪音是众所周知的厉害，但电动的替代品又往往持久力不足，难以实际使用。
Two-stroke, gas-powered tools are famously polluting and loud, but electric variants typically lack the power or durability to really be practical.
这次事件的后果难以估量，波兰斯基现在面临着旷日持久，横跨两大洲的法律战，但是从公众意见来看，他的形象已经岌岌可危。
The ramifications of that will be difficult to measure. Polanski now faces a long legal battle that will span two continents.
持久性有机污染物是一种非常难以处理的污染物形式。
Persistent organic pollutants are a particularly problematic form of pollution.
由于聚丙烯纤维的这种化学惰性和极大的疏水性，使得用一般的染料染色难以获得满意的渗透性和染料在纤维内部的持久性，各项牢度均很差。
On account of the chemical inertia and huge hydrophobic about polypropylene, generic dye is difficult to dye the fibre and can only gain dissatisfiable permeability and poor permanence of dye.
它所具有的隐蔽性、全面性、持久性以及学生接受素质教育的主动性，是其他教育形式所难以比及的。
Its impact is hidden, comprehensive, and persistent with initiative on students' part, all of which is incomparable to other educational forms.
它所具有的隐蔽性、全面性、持久性以及学生接受素质教育的主动性，是其他教育形式所难以比及的。
Its impact is hidden, comprehensive, and persistent with initiative on students' part, all of which is incomparable to other educational forms.
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