Dedicated oracle Server mode and Shared Server Mode

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I. Shared Server mode.

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The Shared Server mode is also called the multi-thread server mode. In this mode, the Oracle database allows multiple user processes to share very few server processes. Therefore, the number of concurrent users can be greatly increased. If the dedicated server mode is used, each user's process needs its own dedicated server process when connecting to the database. That is to say, the client process corresponds to the server process one by one.

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In the Shared Server mode, multiple users can share one server process. That is to say, the client process and the server process are many-to-one. This is mainly implemented through the scheduling program. The scheduler directs multiple database access Session requests to a shared queue. A idle server process in the server process sharing pool obtains a request from the queue in sequence. That is to say, a small server process sharing pool can provide services for a large number of clients.
The advantages and disadvantages of shared servers can be summarized in two sentences. The advantage is that the client process is many-to-one, increasing the number of users supported by the database. The disadvantage is that each user shares a process, which affects the user's database access performance.
Specifically, you can select the Shared Server mode in the following scenarios.

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1. There are many front-end clients.
When a large number of users need to connect to the database and need to effectively use available system resources, they need to consider using the Shared Server mode. Specifically, network application software, such as the ERP system, is currently used in Client/Server mode. On the one hand, because of the large number of users, on the other hand, enterprises have limited funds, so they purchase General servers. These servers are subject to some hardware restrictions, such as database systems and front-end application servers using a uniform server. Therefore, databases are often required to make full use of hardware resources to reduce conflicts between the two.
In this case, the Shared Server mode is usually used, which is suitable.

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2. The server memory limit is relatively large.
In Shared Server mode, when the number of connected users increases, the memory usage will not increase much. Because they share a server process. Therefore, from this perspective, the Shared Server mode can reduce memory usage. However, in dedicated server mode, memory usage is almost proportional to the number of users.
Therefore, if you deploy an Oracle database on some old servers, the upgrade of the memory on the main board is limited. Therefore, in order to get a good database performance, the Shared Server mode is usually used. In this way, the number of users who access the database at the same time increases, and the memory will not have much impact. Can greatly reduce the memory pressure.

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3. Some specific features require the Shared Server mode.
Although the Shared Server mode and dedicated server mode are common in most cases, most of the functions of the Oracle database system are supported. However, some specific functions still need to be enabled by the database administrator in the Shared Server mode. Typical examples include connection sharing, connection centralization, and Server Load balancer for Oracle database servers. They can only run in shared mode.

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Server Load balancer is used to implement multi-host database sharing in a cluster environment to ensure high availability of applications. At the same time, it can automatically achieve parallel processing and load balancing. It can also achieve Fault Tolerance and Non-breakpoint recovery in the case of database faults. Therefore, in some application scenarios with high performance and stability requirements, such as banks, Server Load balancer technology is often used. In this case, the database administrator needs to consider using the Shared Server mode When configuring the database.

Ii. dedicated server mode.
In dedicated server mode, the database server requires each user to have a dedicated server process. That is to say, each server has a server process. The database server sends the existing Server process geology back to the client, and then the client resends the connection request to the provided server geology, Which is compared with the dedicated server. The dedicated server mode has a one-to-one correspondence between the client and the server process, so it may have a better performance. However, when there are many users, the hardware resources on the server, especially the memory, will generate a great deal of pressure.
If the Enterprise Application Scenario meets the following characteristics, the dedicated annual server model can achieve better results.
1. There are only a few clients.
If few users connect to the database, the dedicated server mode is the first choice. For example, if the enterprise front-end is a financial management system, the number of users will be relatively small. Because it usually involves only one department. However, the data volume is large. As we know, every transaction requires a detailed record in the financial system. Therefore, although it is only used by a financial department, its record volume is often the sum of records of other departments. It is wise to use the dedicated server mode when there are many records and few connected users.
2. database system built for the data warehouse.
Data Warehouse is a very typical application of database technology. It is a subject-oriented, integrated, time-varying, and non-loss-prone data set that supports the decision-making process of management departments. Like Oracle databases, hybriddb for MySQL is a relational database. Its records are stored in tables and can be queried in a unified structured language. The main purpose of using a data warehouse is to promptly complete business processing and respond to customers in a timely manner.
Although relational databases can meet the needs of large-scale database applications, they cannot be simply stacked and directly used as data warehouses. Because the data warehouse is mainly used to process multi-dimensional data. The method for storing records is different from that for ordinary ones. The data warehouse stores records in an array, that is, there is no uniform rule to follow, and there is no uniform multi-dimensional model to follow. He can only purchase and classify records by their category. Although traditional two-dimensional databases cannot be simply built into data warehouses. However, when designing a data warehouse, it is not to say that it is completely different, but to use the existing Oracle database system to process data and integrate the information, to construct a data warehouse meeting different needs.
Therefore, if the database is built to implement a data warehouse, the dedicated server mode must be used. This is a mandatory requirement for Oracle databases.
3. online transaction processing system.
The online transaction processing system (OLTP. In this application, what mode is better? There is no uniform standard in the industry. Some say that because the online transaction processing system is used by a large number of users, it should adopt the shared connection server mode. Some also say that the online transaction processing system has high requirements on timeliness, the Shared Server mode may have a long wait time. Therefore, the dedicated connection server mode should be used. I prefer the following opinion.
An online transaction processing system generally involves many long transactions and large transactions. For example, some operations of a user must be treated as a transaction. In this case, if the number of user requests is greater than the number of processes on the Shared Server, queuing occurs. Assume that a shared server process is executing a long transaction, so the Request queue needs to wait. Until the transaction is completed. From the client perspective, the response time of the customer request is extended. Therefore, when the number of user connection requests is more than that of the shared process, the shared connection of long transactions will inevitably lead to the queuing of the shared process. The longer the transaction, the longer the queue time, and the longer the user response time. If such a vicious circle goes on, many online transaction jobs will be affected to varying degrees. Therefore, if the online transaction processing system meets two conditions (the number of user connection requests is greater than that of the shared process and most of the transactions are long transactions or large transactions ), the dedicated server connection mode is more efficient than the Shared Server connection mode. To ensure the normal operation of the online transaction processing system, we recommend that the database administrator configure the dedicated server connection mode for it. If one of the two conditions is not met, the shared connection mode is more reasonable.