Cosmos DB NoSQL Connection Pooling in FastAPI

Hi Samruddha K - iProgrammer,

Greetings!

For Azure Cosmos DB NoSQL, the SDK itself handles connection management efficiently, including internal pooling and multiplexing of connections, especially when using the recommended singleton pattern. This means that explicitly implementing a connection pool at the application level is generally not necessary for most use cases.

While it's true that the SDK does handle connections automatically, implementing client-side connection pooling can still provide significant benefits.

The Azure Cosmos DB Python SDK (specifically azure-cosmos) is designed to manage HTTP connections internally using a connection pool. This means that in most cases, you do not need to manually implement a connection pool at the application level.

Here are a few points to consider:

1. Use a Singleton CosmosClient Instance: The Azure Cosmos DB Python SDK is designed to be thread-safe and optimized for performance when a single CosmosClient instance is reused across your application. Creating a new client for each request can lead to unnecessary overhead and resource consumption. Instead, initialize the CosmosClient once during your FastAPI application’s startup (e.g., using FastAPI’s lifespan events) and reuse it for all database operations. This approach leverages the SDK’s internal connection management, which is sufficient for handling high traffic, especially with autoscale enabled.
2. Connection Pooling Benefits: By implementing a connection pool, you can maintain a set of open connections that can be reused, which significantly reduces the overhead associated with establishing new connections each time your application needs to interact with the database. This can lead to performance improvements, like faster query response times.

Recommended Approach:

Singleton pattern: It’s generally recommended to instantiate the Cosmos DB client once and reuse it throughout the lifetime of your application. This avoids repeatedly creating new HTTP connections, which can be inefficient and lead to socket exhaustion.

In a FastAPI application, this typically means creating the Cosmos client during startup and sharing it via dependency injection or global state.

I hope this helps clear things up! Please do let us know if you have any follow-up questions or need further assistance.

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