Why NoSQL databases are present

NoSQL that not-only SQL is a good complement to relational databases

relational database is a database based on relational model . So what is a relational model? ? The model for storing data in rows and columns in a two-dimensional table is the relational database . For example : MySQL and the Oracle

with the InternetWebThe rise of the website,more and more shortcomings in relational database exposure,a relational database can handle tens of thousands of timesSQLEnquiry,but for tens of thousands of timesSQLrequest to write data,HDDioIt's not going to be a bird.

Here is a small part of the hard disk and memory what is the difference (memory bar is called memory)

hard disk : c disk, d disk, e disk, all refers to the hard disk. Its appearance is a square box with a platter ( like a disc

Memory Strips : because the hard disk speed is slow, CPU If you run the program, all data is read and written directly from the hard disk, which can affect efficiency. So the CPU will run the software to use the data once from the hard disk call to run fast memory, and then the CPU and memory for data exchange. Memory is volatile memory, and as long as you are disconnected, the data in memory is gone. The memory itself is an integrated circuit board with several chips for storing data. Since this circuit board is generally made into strips, it is called a "memory bar".

sum up :

read Data :CPU read data back from the hard disk to write data from one-time to memory to,onlyCupit's from memory. Read Data  

let's think of a problem. ????? What to do if memory memory is exhausted ? is there no way to use the computer? ?

          Now the main memory bar, with a capacity of 8GB 16GB, Although it's a lot bigger than it used to be. The operating system solves this problem by :

Write Data : The CPU writes the data back directly to the hard disk , if the need for a lot of data , You can first write to the hard disk cache , hard disk cache plays a role in buffering when reading and writing hard drives

The hard disk cache is a separate small chip on the hard disk's circuit board . ( just like memory ) . For example , the CPU to the hard disk to write a large number of fragmented files,theCPU can first throw this heap of files into a faster cache, and then the CPU You can do other things first. The hard disk then writes this heap of fragmented small files from the cache to the hard disk surface. Hard disk caching helps to improve the performance of hard disk's burst read-write and random read/write.

Good , before we get back to our point of , Why does it appear NoSQL Database

example : record the click-through rate of a site post is a very common feature So have you ever thought , , obvious very high

example : voting system , , All the people are starting to request write data to hard disk , Io No more birds. so nosql

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Why NoSQL databases are present