Storing Rows and Columns

A fundamental requirement of a database is to store and retrieve the data. In Relational Database Management Systems (RDBMS) the data is organized into a table that contain the rows and columns. Traditionally the data is stored into blocks of rows. For example a "sales transaction row" may have 30 data items representing 30 columns. Assuming a record occupies 256 bytes, a block of 8KB can hold 32 such records. Again assuming a million such transactions that need to be stored in 32150 blocks per day. All this works well as long as we need the data as ROWS! We want to access one row or a group of rows at a time to process that data, this organization has no issues.

Let us consider if we want to get a summary of total value of type x items that are sold in past seven days. This query need to retrieve 7million records that contain 30 columns each to just process the count of items of types x. All that we need is two columns item type and amount to process this. This type of analytical requirement lead us to store the data in columns. We group the columns together and store them in blocks. It improves the speed of retrieving the columns from the overall table quickly for the purpose of analyzing the data.  

But the column storage has its limitations when it comes to the write and update

With a high volume of social data, where there is high volume of write is needed (like messages and status updates, likes and comments etc.,) , highly distributed, NOSQL based column stores are emerging into mainstream. Apache Cassandra is the new breed of NOSQL column store that was initially developed by Facebook.

So, we have a variety of data base / data stores available now, a standard RDBMS engine with SQL support for OLTP applications, A column based engies for OLAP processing and noSQL based key value pair stores for in-memory processing, highly clustered Hadoop style big data with map/reduce framework for big data processing and noSQL based column stores for high volume social write and read efficiencies. 


Making right choice of data store for the problem in had is becoming tough with many solution options. But that is the job of an architect; Is it not?