ORM connection pooling help?

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Rohan Patel Author
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1 week ago Asked
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2 Replies
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hey everyone, still struggling a bit with the database connections after a deploy, you know, from that last thread. i thought i had it figured out but looks like i'm still missing something crucial.

i've been trying to dig into how my full-stack framework (using a generic ORM, let's say it's like Prisma or SQLAlchemy) handles its database connections, especially after a new deploy or when the app sits idle for a while. it seems like the connections just... vanish. i'm really trying to understand database connection pooling better for this.

i tried looking at the ORM's documentation for connection pooling settings. i found things like pool_size and idle_timeout, and i've tried setting them in my config, but i'm honestly not sure if i'm even putting them in the right place or with the write values. it's all a bit confusing for a newbie.

the problem is, after a deploy, or sometimes after a few hours of low traffic, when a new request comes in, the app just throws a fit trying to talk to the database. it's like the existing connections are dead, and new ones aren't being established properly. restarting the app temporarily fixes it, but that's not a real solution.

here's what i sometimes see in my logs when it happens:

[2023-10-27 14:35:01] ERROR: sqlalchemy.pool.QueuePool - Connection 'psycopg2.connect' was closed by the database.
[2023-10-27 14:35:01] ERROR: my_app.database - Database connection lost. Attempting to reconnect...
[2023-10-27 14:35:02] CRITICAL: my_app.api - Unhandled exception: (psycopg2.OperationalError) server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
    (Background on this error at: https://sqlalche.me/e/20/e3q8)

i'm a complete noob with this stuff, so i'm probably making some really basic mistake. what's the correct way to set up and manage ORM connection pooling in a full-stack framework, especially to prevent these random disconnects after a deploy or during idle periods? any step-by-step guidance for someone totally new to this would be super helpful.

orm database deploy connection pooling

2 Answers

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MD Alamgir Hossain Nahid
Answered 1 week ago
Hello Rohan Patel, Regarding your database connection issues after deployment or during idle periods, the `psycopg2.OperationalError: server closed the connection unexpectedly` is a classic symptom of stale connections in your ORM's connection pool. You mentioned struggling with setting them with the 'write' values โ€“ it's actually 'right' values, a common typo when you're deep in config files! This error indicates that while your application thought it had an open connection, the PostgreSQL server had already terminated it, often due to an idle timeout or a server restart. Proper database connection management within your ORM is crucial here. The key to resolving this lies in configuring your ORM's connection pool to proactively manage and recycle connections, rather than just letting them sit idle and become invalid. Hereโ€™s a breakdown of the crucial settings and how to approach them for robust ORM configuration:
  • pool_size: This sets the maximum number of connections your pool will maintain. A common starting point is between 5 and 20, depending on your expected concurrent load. Don't set it excessively high unless your database can handle hundreds of concurrent connections from a single application instance.
  • max_overflow: This allows the pool to temporarily create connections beyond pool_size to handle short bursts of traffic. A value of 0 to 10 is typical. These overflow connections are closed once they return to the pool and exceed the pool_size limit.
  • pool_recycle: This is arguably the most critical setting for your specific problem. It dictates how often (in seconds) connections are forcibly recycled, regardless of activity. If your PostgreSQL server has an idle connection timeout (e.g., idle_in_transaction_session_timeout or similar network-level timeouts), set pool_recycle to a value *less* than that timeout. For instance, if your database closes connections after 5 minutes (300 seconds), set pool_recycle=299. This ensures connections are refreshed before the database has a chance to close them unexpectedly.
  • pool_pre_ping: Enable this. When set to True, the ORM will issue a lightweight "ping" (e.g., SELECT 1) to the database before using a connection from the pool. If the ping fails, the connection is discarded, and a new one is established. This prevents the application from trying to use a truly dead connection.
  • pool_timeout (or idle_timeout): This specifies the maximum time (in seconds) a connection can remain idle in the pool before being closed. This helps release resources if connections aren't being used. A value like 30 to 60 seconds is often reasonable.
  • Configuration Placement: Ensure these settings are passed directly to your ORM's engine or client initialization. For SQLAlchemy, this would be within the create_engine() call. For other ORMs, consult their specific documentation for where to define pooling parameters (e.g., in your application's configuration file or directly in the client constructor).
0
Rohan Patel
Answered 1 week ago

This is exactly what I needed, really appreciate you breaking it down like that, and honestly, this community is just so helpful.

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