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Summary of Large Database Application Solutions

Category Programming Technology

With the widespread adoption of Internet applications, the storage and access of massive amounts of data have become bottleneck issues in system design. For a large Internet application, daily PVs in the millions or even hundreds of millions undoubtedly impose a considerable load on the database. This poses significant challenges to the stability and scalability of the system.

I.

A load-balanced cluster is composed of a group of independent computer systems connected by regular or dedicated networks, linked together by routers, with each node working in collaboration, sharing the load, and balancing the pressure. To the client, the entire cluster can be seen as a single independent server with ultra-high performance.

1. Implementation Principle

To implement load balancing technology for databases, you first need a control end that can manage connections to the database. Here, it intercepts the direct connection between the database and the program, with all programs accessing this intermediate layer, and then the intermediate layer accesses the database. In this way, we can specifically control access to a particular database, and then we can also adopt effective balancing strategies based on the current load of the database to adjust which database to connect to each time.

2. Implementing Synchronous Data Across Multiple Databases

For load balancing, the most important thing is that the data on all servers is synchronized in real time. This is a necessity for a cluster because if the data is not real-time and synchronized, then the data read by a user from one server will differ from the data read from another server, which is not permissible. Therefore, it is essential to implement data synchronization between databases. In this way, when querying, there can be multiple resources to achieve balance. A commonly used method is Moebius for SQL Server clusters. Moebius for SQL Server clusters adopt the method of residing the core program in the database of each machine, which is called the Moebius for SQL Server middleware. Its main function is to monitor changes in the database data and synchronize the changes to other databases. After the data synchronization is completed, the client will receive a response. The synchronization process is completed concurrently, so the time to synchronize to multiple databases is basically the same as synchronizing to a single database. In addition, the synchronization process is completed in a transactional environment, ensuring the consistency of multiple copies of data at any given time. It is precisely because of the innovation of Moebius middleware residing in the database that the middleware not only knows the changes in the data but also knows the SQL statements that cause the data changes. Based on the type of SQL statement, it intelligently adopts different data synchronization strategies to ensure the minimization of data synchronization costs.

If there are few data records and the content is not large, then synchronize the data directly.

If there are few data records, but they include large data types, such as text, binary data, etc., first compress the data and then synchronize it to reduce the occupation of network bandwidth and the time used for transmission.

If there are many data records, the middleware will obtain the SQL statements that cause data changes, then parse the SQL statements, analyze their execution plan and execution cost, and choose whether to synchronize data or synchronize SQL statements to other databases. This situation is very useful when adjusting the table structure or batch updating data.

3. Advantages and Disadvantages

(1) Strong scalability: When the system requires higher database processing speed, simply adding database servers can achieve expansion.

(2) Maintainability: When a node fails, the system will automatically detect the failure and transfer the application of the faulty node, ensuring the continuous operation of the database.

(3) Security: Because data is synchronized across multiple servers, data set redundancy can be achieved, ensuring security through multiple copies of data. In addition, it successfully places the database within the internal network, better protecting the security of the database.

(4) Ease of use: It is completely transparent to the application, and the cluster exposes only one IP.

(1) Cannot distribute the load according to the processing capacity of the web server.

(2) If the load balancer (control end) fails, it will cause the entire database system to collapse.

II. Database Read-Write Separation

  1. Implementation principle: Read-write separation simply means separating the read and write operations of the database to correspond to different database servers. This can effectively reduce the database pressure and also reduce IO pressure. The master database provides write operations, and the slave database provides read operations. In fact, in many systems, the main operation is reading. When the master database performs a write operation, the data must be synchronized to the slave database to effectively ensure the integrity of the database.

(Ebay's read-write ratio is 260:1, eBay's read-write separation)

(Microsoft database distribution)

  1. Implementation method: In MS SQL Server, database replication can be achieved through the use of publication definitions to implement read
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