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copied!<h2>Manage Connections</h2> <p>The major benefit of connection pooling for a single-thread server like Mongrel/Passenger/etc is that the connection is established/maintained in a Rack handler outside the main Rails request processing. This allows for a connection to be established once vs. many times as it's used in different ways. The goal is to re-use the established connection and minimize the number of connections. This should prevent having to reconnect within a given request processing cycle and possibly even between requests (if I recall correctly).</p> <h2>Multiple Concurrent Connections</h2> <p>Although most use cases (Mongrel/Passenger) are single threaded and can only use a single connection at a time - there is JRuby and environments/app servers that have full multi-threaded support. Rails has been thread safe since 2.2</p> <ul> <li><p>Connection pooling is handled inside of ActiveRecord, so all application servers should behave basically the same.</p></li> <li><p>The database connection pool starts out empty and creates connections over time according to demand. The maximum size of this pool defaults to 5 and is configured in database.yml.</p></li> <li><p>Requests and users share connections from this pool. A request checks out a connection the first time it needs to access the database and then checks the connection back in at the end of the request. </p></li> <li><p>If you use Rails.threadsafe! mode, then multiple threads might be accessing multiple connections at the same time, so depending on the request load you might have multiple threads contending for a few connections.</p></li> </ul> <p><strong>You can change accordingly, If you are using single threaded app. Default is 5 as per most user's need, as now a day its normal to have a multithreaded app.</strong></p>

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