This sample describes how to use FireDAC in a multithreaded environment. In a multithreaded application, where each thread starts, establishes a connection, performs a certain short task, and releases the connection, the repetitive connection establishments may lead to performance degradation across the whole system. To avoid this, the application can use the connection pooling.
This application shows the difference of time used when using pooling to establish many connections to a database.
You can find the TFDConnection\Pooling sample project at:
- Start | Programs | Appmethod 1.16 | Samples and then navigate to:
- Object Pascal\DataBase\FireDAC\Samples\Comp Layer\TFDConnection\Pooling.
- Subversion Repository for Object Pascal: http://sourceforge.net/p/radstudiodemos/code/HEAD/tree/branches/RadStudio_XE8//Object%20Pascal/Database/FireDAC/Samples/Comp%20Layer/TFDConnection/Pooling.
This sample uses the Use Connection Definition drop-down menu to select a connection definition.
Click Run to execute mutiple threads that establish a connection to the database and perform SQL queries on it. To enable pooling, select Run pooled before clicking Run.
The Total executions and the Total time labels show the number of executed SQL queries and the amount of time used. The time is considerably inferior when using pooling.
How to Use the Sample
- Navigate to the location given above and open:
- Object Pascal: Pooling.dproj
- Press F9 or choose Run > Run.
- Select a connection definition from the Use Connection Definition drop-down menu. Once a connection is selected the Run button is enabled.
- Select Run pooled to use pooling.
- Click Run to start creating the connections to the database. It executes 10 threads to the database.
- Use Connection Definition drop-down menu:
The menu shows all the connections defined on the file at C:\Users\Public\Documents\Embarcadero\Studio\FireDAC\FDConnectionsDefs.ini.
- Run button:
When clicked, the sample starts 10 threads connecting to the database. It uses the TFDCustomManager.ConnectionDefs property from a TFDManager to access the connection definition selected from the Use Connection Definition drop-down menu.
The standard simplification is to create and use for each thread a dedicated connection object working with the database. In this case, no additional serialization is required.
- Run pooled check box:
When this option is selected, the Pooled argument of the connection setting is set to True. The connection pooling can be enabled only for a persistent or private connection definition by setting Pooled to True.
Database connection pooling is a method used to keep database connections open so they can be reused by others. Opening a database connection is an expensive operation, so pooling keeps the connections active so that, when a connection is later requested, one of the active ones is used in preference to opening another one.