为什么在memcached中存在硬编码的块限制(压缩后为0.5兆)？有没有人重新编译他们的书呢？我知道我不应该发送像这样的大块，但是这些额外的大块不时发生在我身上，造成了严重破坏。

解决方案

回答

这个问题曾经在官方常见问题解答中

我可能会遇到哪些内存缓存限制？ (平装机)

去引用：

The simple limits you will probably see with memcache are the key and 
  item size limits. Keys are restricted to 250 characters. Stored data 
  cannot exceed 1 megabyte in size, since that is the largest typical 
  slab size."

常见问题解答现已修订，现在有两个单独的问题涉及此问题：

最大密钥长度是多少？ (250字节)

The maximum size of a key is 250 characters. Note this value will be
  less if you are using client "prefixes" or similar features, since the
  prefix is tacked onto the front of the original key. Shorter keys are
  generally better since they save memory and use less bandwidth.

为什么将项目的大小限制为1 MB？

Ahh, this is a popular question!
  
  Short answer: Because of how the memory allocator's algorithm works.
  
  Long answer: Memcached's memory storage engine (which will be
  pluggable/adjusted in the future...), uses a slabs approach to memory
  management. Memory is broken up into slabs chunks of varying sizes,
  starting at a minimum number and ascending by a factorial up to the
  largest possible value.
  
  Say the minimum value is 400 bytes, and the maximum value is 1
  megabyte, and the factorial is 1.20:
  
  slab 1 - 400 bytes slab 2 - 480 bytes slab 3 - 576 bytes ... etc.
  
  The larger the slab, the more of a gap there is between it and the
  previous slab. So the larger the maximum value the less efficient the
  memory storage is. Memcached also has to pre-allocate some memory for
  every slab that exists, so setting a smaller factorial with a larger
  max value will require even more overhead.
  
  There're other reason why you wouldn't want to do that... If we're
  talking about a web page and you're attempting to store/load values
  that large, you're probably doing something wrong. At that size it'll
  take a noticeable amount of time to load and unpack the data structure
  into memory, and your site will likely not perform very well.
  
  If you really do want to store items larger than 1MB, you can
  recompile memcached with an edited slabs.c:POWER_BLOCK value, or use
  the inefficient malloc/free backend. Other suggestions include a
  database, MogileFS, etc.