Keys are unique identifiers that you provide as a parameter when
you perform any operation on data. The following applies to
keys: Keys are strings, typically enclosed by quotes for any
given SDK. No spaces are allowed in a key. Separators and
identifiers are allowed, such as underscore: 'person_93847'. A
key must be unique within a bucket; if you attempt to store the
same key in a bucket, it will either overwrite the value or
return an error in the case of Maximum key size is 250 bytes.
Couchbase Server stores all keys in RAM and does not remove
these keys to free up space in RAM. Take this into consideration
when you select keys and key length for your application. This
last point about key size is important if you consider the size
of keys stored for tens or hundreds of millions of records. One
hundred million keys which are 70 Bytes each plus meta data at
150 Bytes each will require about 45 GB of RAM for document meta
data.