I found some info about limitations for document in Couchbase: /thread/key-length - that the maximum length of the key is 250 bytes. But couldn't find any official one.
Can someone confirm the maximum length of a key for Couchbase document?
What are other limitations for keys, and what are good practices for them?
What about indexes (keys for map functions)?
My use case is that I want to store documents identified by url. The straight forward solution is to indicate the documents by url. Assuming that there are urls bigger than 250 bytes, I need to choose other key - eg md5(url) and put url as an element of the document. Is this good model for Couchbase?
Yes there is a a 250 byte restriction to keynames in Couchbase Server. Your idea to hash the URLs should work great.
The bytes that make up a key also need to be legal utf-8 (you can store and retrieve non-string keys, but they wont' participate in the full set of Couchbase features, like views and cross datacenter replication).
Key in map reduce views must be utf-8, and are limited to 65kb in length.