“Hash and Range Primary Key” means that a single row in DynamoDB has a unique primary key made up of both the hash and the range key. For example with a hash key of X and range key of Y, your primary key is effectively XY. You can also have multiple range keys for the … Read more
Consistency means that data is the same across the cluster, so you can read or write from/to any node and get the same data. Availability means the ability to access the cluster even if a node in the cluster goes down. Partition tolerance means that the cluster continues to function even if there is a … Read more
I think there are some essential differences between CouchDB and Couchbase Server that need to be pointed out. I will not write about the advantages of switching from CouchDB to the Couchbase Server because those are described pretty much everywhere (see The Future of CouchDB by Damien Katz or Couchbase vs. Apache CouchDB by Couchbase). … Read more
Same as the updating existing collection field, $set will add a new fields if the specified field does not exist. Check out this example: > db.foo.find() > db.foo.insert({“test”:”a”}) > db.foo.find() { “_id” : ObjectId(“4e93037bbf6f1dd3a0a9541a”), “test” : “a” } > item = db.foo.findOne() { “_id” : ObjectId(“4e93037bbf6f1dd3a0a9541a”), “test” : “a” } > db.foo.update({“_id” :ObjectId(“4e93037bbf6f1dd3a0a9541a”) },{$set : … Read more
First, hstore is a contrib module, which only allows you to store key => value pairs, where keys and values can only be texts (however values can be sql NULLs too). Both json & jsonb allows you to store a valid JSON value (defined in its spec). F.ex. these are valid JSON representations: null, true, … Read more
I would say, it depends on kind of dev team you are and your application needs. For example, if you require a lot of querying, that mostly means it would be more work for your developers to use Redis, where your data might be stored in variety of specialized data structures, customized for each type … Read more
This will return all documents with a key called “IMAGE URL”, but they may still have a null value. db.mycollection.find({“IMAGE URL”:{$exists:true}}); This will return all documents with both a key called “IMAGE URL” and a non-null value. db.mycollection.find({“IMAGE URL”:{$ne:null}}); Also, according to the docs, $exists currently can’t use an index, but $ne can. Edit: Adding … Read more
Of C, A & P (Consistency, Availability & Partition tolerance) which 2 are more important to you? Quick reference, the Visual Guide To NoSQL Systems MongodB : Consistency and Partition Tolerance CouchDB : Availability and Partition Tolerance A blog post, Cassandra vs MongoDB vs CouchDB vs Redis vs Riak vs HBase vs Membase vs Neo4j … Read more
Horizontal scaling means that you scale by adding more machines into your pool of resources whereas Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing machine. An easy way to remember this is to think of a machine on a server rack, we add more machines across the horizontal … Read more