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This article mainly explains "what is the principle of database middleware". Interested friends may wish to take a look at it. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "what is the principle of database middleware"?

Key points of database middleware design

To be able to parse SQL

Can support read-write separation

Can support load balancing read from the library

Support sub-database operation

Support sub-table operation

Support cross-library association queries

Support for transaction processing

Primary key ID generation

Data source management

Database split

Advantages

Shortcoming

Slicing rule: the most important point of horizontal split

The splitting rules are abstract, and the join operation can basically be done in the database.

There is no performance bottleneck of single library big data and high concurrency.

There is less modification on the application side.

Improve the stability and load capacity of the system.

Split rules are difficult to abstract

The consistency of fragment transaction is difficult to solve.

It is difficult to expand the data many times and has a great amount of maintenance.

Poor performance of cross-library join

Range: time, numeric

List: by region, by organization, by category

Hash: hash (a field)% number of shards, consistent hash

Compound multiple ways

Advantages:

Shortcoming

After the split, the business is clear and the split rules are clear.

It is easy to integrate or expand between systems

Data maintenance is simple

Some business tables can not be join, so they can only be solved by interface, which increases the complexity of the system.

Due to the different limitations of each business, there is a performance bottleneck of a single database, so it is not easy to expand data and improve performance.

Transaction processing is complex

Vertical split: for example, according to the order table and the user table, put them into different databases

Horizontal split: split tables with large amounts of data, such as splitting user data into different libraries for storage

The technical difficulties of sub-database and sub-table: whether it is vertical split or horizontal split, the following difficulties will be introduced:

The problem of introducing distributed transactions

The problem of cross-node join

Cross-node merge sorting paging problem

Multi-data source management problem

Implementation Mode of Database Middleware

Client mode: integrate the database middleware module in the application, configure one or more data sources needed by the management application, and access each data source, complete the data integration in the module, suitable for small systems, typically sharding-jdbc

Server agent mode: all data sources are managed uniformly through the intermediate agent layer, and the back-end database cluster is transparent to the front-end applications and easy to expand the database. Stand-alone services provide stronger processing power and are suitable for large and complex systems, typically Mycat

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