# Connection pooling Every project has a connection pool, and your connection string already goes through it. A client holds a database connection only during a transaction, so a lot of clients cost your database very little. A plain project's pool is [PgBouncer](https://www.pgbouncer.org), running beside its database. A [cluster](https://docs.snoutdata.com/stack/lepis/operations#connection-pooling) pools in its router. ## The two modes | Mode | What a client holds | Use it for | | --- | --- | --- | | **Transaction**, the default | A database connection only during a transaction | Web apps, APIs, functions, and most drivers and ORMs | | **Session** | A database connection of its own for as long as it is connected | LISTEN, temporary tables that outlive a transaction, session advisory locks and SQL `PREPARE` | ## How big the pool is The pool grows with the project's plan, and many clients use each of its database connections. | | Free | Plus | Pro | | --- | --- | --- | --- | | Clients connected at once | 500 | 1,000 | 2,000 | | Database connections in the pool | 20 | 40 | 80 | Each plan's pool has 20 database connections for every 512 MB of the project's memory, and a dedicated project's follows the memory of its size. A cluster has this many on each of its nodes. In session mode, each client has a connection of its own, up to the session mode number on [limits](https://docs.snoutdata.com/cloud/limits). ## Choose the mode In the [dashboard](https://dashboard.snoutdata.com), the project's **Settings**, **Database access**, **Connection pooling**. From the CLI (0.23.0 and up): ```sh snoutdata db pool # which mode the project is in snoutdata db pool session snoutdata db pool transaction ``` Reading the mode needs the project's infrastructure settings. Changing it needs Full access or the owner. The connection string stays the same in both modes. ## What works in transaction mode - **Transactions**, whole, along with what lasts as long as one: `SET LOCAL` and `pg_advisory_xact_lock`. - **Drivers' prepared statements**, the ones a driver sends through the Postgres protocol. - **These settings, per client:** `search_path`, `TimeZone`, `DateStyle`, `IntervalStyle`, `application_name`, `client_encoding` and `standard_conforming_strings`. ## What goes straight to the database - A person using [database sign-in](https://docs.snoutdata.com/cloud/database-sign-in). - The dashboard's SQL editor. - The project's own services, such as the data API and Auth. - The project's [containers](https://docs.snoutdata.com/stack/containers), over their internal address.