While I am barely scratching the surface with CoudhDB, I would go out on the limb and suggest that it is next to impossible to pre-determine how happy you will end up being with CouchDB as a general replacement to MySql or any other relational database because they are two different things. Therefore, you will more likely need to start by not comparing them and instead more precisely focusing on what it is that you are trying to achieve with CouchDB. Since you are familiar with MySql, what is it about it that brought you looking for an alternative? Those are perhaps the most important questions because whatever the answers are, those answers would most likely help to explain at least some of the differences as well as some of the reasons why they can not be that closely compared. Being new to CouchDB, it might be quite useful to also consider whether you intend to host it yourself or (like me) you plan to use www.IrisCouch.com or www.Cloudant.com.
In any case, consider what would happen with MySql if it had no indices and if it had to scan all of the records in queried tables. Well, much the same thing happens with CouchDB without any views. However, if you add some indices onto main MySql tables and columns then you are able to more dynamically and more efficiently query those table columns in variety of non pre-determined combinations. This is not the same in CouchDB. CouchDB being "schemaless" means that you can indeed create documents of various "shapes". However, you still have to have a very "strongly typed schema" - both in your head and in your design docs code, in order to be able to get anything useful out of CouchDB, beyond directly accessing individual documents by their build-in "_id". Specifically, it means that you will need to pre-determine each and every index/sort combination by which you need to access those documents. Once that is done, then CouchDB seems to be both efficient and scalable in what it does. Finally, before you consider any of this, let's wait for our technical friends to either correct and/or to reduce to nonsense whatever I just wrote. ;) HTH, teslan
