Which, if any, of the NoSQL databases can provide

Question

Which, if any, of the NoSQL databases can provide stream of changes to a query result set?

Could anyone point me at some examples?

Firstly, I believe that none of the SQL databases provide this functionality - am I correct?

I need to be able to specify arbitrary, simple queries, whose equivalent in SQL might be written:

SELECT * FROM accounts WHERE balance < 0 and balance > -1000;

I want an an initial result set:

id: 100, name: Fred, balance: -10
id: 103, name: Mary, balance: -200

but then I want a stream of changes to follow, forever, until I stop them:

meta: remove, id: 100
meta: add,    id: 104, name: Alice, balance: -300
meta: remove, id: 103
meta: modify, id: 104, name: Alice, balance: -400
meta: modify, id: 104, name: Alison, balance: -400
meta: add,    id: 101, name: Clive, balance: -200
meta: modify, id: 104, name: Alison, balance: -100
...

Note: I'm not talking about streaming large result sets. I'm looking for a soft-realtime stream of changes.

Also, it needs to scale out, if possible.

Thanks,

Chris.

Answer 1

this type of thing should be done in the app, not the database.

Meaning, every time you make a change, it should be recorded as a new record. Not a modification to the record. There's a whole lot more intelligence you can add to your app if you do it this way

Answer 2

CouchDB has a changes feed. Basically it's a block chain, or a history of every change in the database since inception. You can get the feed via JSON, JSONP, long polling or as a continuous stream and write applications that respond to changes in the database.

Here's the changes feed from my blog

To learn more check out this section of the CouchDB guide