1. What is? NoSQL database ?NoSQL and RDBMS What's the difference? ? Under what circumstances are they used and not used NoSQL database ?

         NoSQL Yes no relational database ,NoSQL = Not Only SQL.

       Structured data used in relational database ,NoSQL The key value pair is used to store data .

       Dealing with unstructured / Semi structured big data ; When expanding horizontally ; Priority can be given to the use of dynamically increasing data items at any time NoSQL database .

       Considering the maturity of the database ; support ; Analysis and business intelligence ; Management and professional issues , Priority should be given to relational databases .

2. What are the non relational databases ?

       Membase,MongoDB,Hypertable

3.MySQL and MongoDB What is the basic difference between them ?

         The difference between relational database and non relational database , That is, different data storage structures .

4.MongoDB What are the characteristics of ?

(1) Document oriented (2) High performance (3) High availability (4) Easy to expand (5) Rich query language

5. MongoDB Do you support stored procedures ? If you support it , How to use it? ?

         MongoDB Support stored procedures , It is javascript Written , Save in db.system.js In the table .

6. How to understand MongoDB Medium GridFS mechanism ,MongoDB Why GridFS To store files ?

  GridFS Is a way to store large files in the MongoDB Document specification in . use GridFS Large files can be separated into multiple small documents for storage , In this way, we can effectively save large documents , And it's solved BSON The problem of limited objects .

7. Why? MongoDB The data file is very large ?

  MongoDB In order to prevent file fragmentation, pre allocation of space is adopted .

8. When updating a block that is being migrated (Chunk) What happens when the document is on ?

   The update operation occurs immediately on the old block (Chunk) upper , The changes are then copied to the new shard before ownership is transferred .

9.MongoDB stay A:{B,C} Index on , query A:{B,C} and A:{C,B} Do you use indexes ?

   can't , Only in A:{B,C} Use index on .

10. If a slice (Shard) Stop or slow , What happens when you start a query ?

   If a slice stops , Unless the query is set “Partial” option , Otherwise, the query returns an error . If a slice responds slowly ,MongoDB Will wait for its response .

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