MongoDB doesn’t support server side foreign key relationships, normalization is also discouraged. You should embed your child object within parent objects if possible, this will increase performance and make foreign keys totally unnecessary. That said it is not always possible, so there is a special construct called DBRef which allows to reference objects in a … Read more
So I’ve been trying to figure out the real bottom-line when it comes to NoSQL vs RDBMS myself, and always end up with a response that doesn’t quite cut it. In my search there are really 2 primary differences between NoSQL and SQL, with only 1 being a true advantage. ACID vs BASE – NoSQL … Read more
Here’s a quote from a recent blog post from Dare Obasanjo. SQL databases are like automatic transmission and NoSQL databases are like manual transmission. Once you switch to NoSQL, you become responsible for a lot of work that the system takes care of automatically in a relational database system. Similar to what happens when you … Read more
Hadoop is basically 3 things, a FS (Hadoop Distributed File System), a computation framework (MapReduce) and a management bridge (Yet Another Resource Negotiator). HDFS allows you store huge amounts of data in a distributed (provides faster read/write access) and redundant (provides better availability) manner. And MapReduce allows you to process this huge data in a … 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
On creating table set your field as JSON datatype. CREATE TABLE `person` ( `name` json DEFAULT NULL ); And Insert JSON data into it, INSERT INTO `person` (`name`) VALUES (‘[“name1”, “name2”, “name3”]’); Or Insert JSON data by Key:Value INSERT INTO person VALUES (‘{“pid”: 101, “name”: “name1”}’); INSERT INTO person VALUES (‘{“pid”: 102, “name”: “name2”}’); Select … Read more
MongoDB stores data in a binary format called BSON which supports these numeric data types: int32 – 4 bytes (32-bit signed integer) int64 – 8 bytes (64-bit signed integer) double – 8 bytes (64-bit IEEE 754 floating point) There’s no exact value fixed-point equivalent to mySQL’s decimal type in MongoDB, but you can store 64-bit … Read more
It is very easy to misunderstand the CAP properties, hence I’m providing some illustrations to make it easier. Consistency: A query Q will produce the same answer A regardless the node that handles the request. In order to guarantee full consistency we need to ensure that all nodes agree on the same value at all … Read more
check with either: ps -edaf | grep mongo | grep -v grep # “ps” flags may differ on your OS or /etc/init.d/mongodb status # for MongoDB version < 2.6 /etc/init.d/mongod status # for MongoDB version >= 2.6 or service mongodb status # for MongoDB version < 2.6 service mongod status # for MongoDB version >= … Read more