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移除书签Since postgresql 14, its client library provides a pipelining mode interface. In pipelining mode, new sql requests can be sent directly to the server without waiting for the result of the previous request to return (this is consistent with the concept of HTTP pipelining), For details, please refer to Pipeline mode. This mode is very helpful for performance, allowing fewer database connections to support larger concurrent requests. drogon began to support this mode after version 1.7.6, drogon will automatically check whether libpq supports pipeline mode, if so, all requests sent through drogon’s DbClient are in pipeline mode.
However, creating a synchronization point for each sql statement also has a certain performance overhead, so drogon provides an automatic batch mode in which instead of creating a synchronization point after each sql statement, a synchronization point is created after several sql statements. the rules for creating a synchronization point in the same connection are as follows:
- A synchronization point must be created after the last sql in an EventLoop loop;
- Create a synchronization point after a sql that writes to the database;
- Create a synchronization point when the number of consecutive SQL statements after the last synchronization point reaches the upper limit;
- A failed sql will cause its previous sql statement to be rolled back after the last synchronization point, but the user will not receive any notification, because no explicit transaction is used;
- The judgment of writing database is based on simple keyword matching (insert, update, etc. ), which does not cover all cases, such as the case of calling stored procedures through select statements, so although drogon strives to reduce the negative effects of automatic batch mode, it is not completely safe;
Therefore, automatic batch mode is helpful to improve performance, but it is not safe. It is up to the user to decide under what circumstances to use it. For example, to execute pure read-only sql statements via the DbClient in automatic batch mode.
When using the newPgClient interface to create a client, set the third parameter to true to enable automatic batch mode; When using a configuration file to create a client, set the auto_batch option to true to enable automatic batch mode for the client;
