What is a valid key?

Steven Grimm sgrimm at facebook.com
Wed Dec 19 18:36:56 UTC 2007

In my opinion:

A key can be up to 250 bytes. It may not contain:
   null (0x00)
   space (0x20)
   tab (0x09)
   newline (0x0a)
   carriage-return (0x0d)

Beyond that, memcached shouldn't care. If your keys are UTF-8, fine.  
If not, fine -- just so long as they don't exceed 250 bytes, memcached  
will just treat them as binary blobs.

UTF-8, for those who don't know, cannot introduce any of the above  
forbidden characters as part of its multibyte sequences. The bytes in  
a UTF-8 sequence are always in the 0x80-0xFF range (actually more  
restricted than that.)

UTF-16 or UTF-32 would likely cause problems, but that's fine -- the  
rules above, being based on raw bytes, will pretty much imply that.


On Dec 19, 2007, at 10:30 AM, Dustin Sallings wrote:

> 	I just got a bug report for my client regarding multibyte  
> characters within a key.  In order to fix it, I need to know what  
> *should* be allowed in a key.
> 	The protocol document is fairly vague as far as what makes up a  
> key.  It says some specific characters that *aren't* valid, but  
> seems to have been written with an ASCII mindset.
> 	In the binary protocol, we have a lot of freedom, but that freedom  
> doesn't extend to the text protocol.
> 	Should we constrain keys to ASCII, or force clients to understand  
> UTF-8 (or some other specific encoding)?
> -- 
> Dustin Sallings

More information about the memcached mailing list