Connection pooling

As explained in 100 Go Mistakes and How to Avoid Them

A database connection pool is a managed collection of reusable database connections that are allocated to operations and returned for later use.

A common mistake is treating sql.Open as a single database connection. It returns an *sql.DB that manages reusable connections, which may be in use by another goroutine or idle for later operations. section 10.4.2

Tune the pool according to database capacity and request behavior:

• SetMaxOpenConns limits simultaneous database connections; leaving it unlimited can exceed what the database handles. section 10.4.2
• SetMaxIdleConns controls reusable idle connections; increasing it can reduce reconnects during concurrent requests. section 10.4.2
• SetConnMaxIdleTime and SetConnMaxLifetime close connections after configured idle or total lifetimes. section 10.4.2

When the pool is full

With five maximum connections, four ongoing connections leave one slot. A new query reuses an idle connection; without an idle connection, it creates one if a slot remains or waits until one becomes available. section 10.4.2

The same tradeoff appears in Go's HTTP client. Connections are reused, but MaxIdleConnsPerHost defaults to two; repeated parallel requests to one host can therefore cause reconnects and higher latency. section 10.7.1

Figure 10.1 A connection pool with five connections

Use the five-connection diagram to trace idle connections, active connections, available capacity, reuse, creation, and waiting. section 10.4.2

How 100 Go Mistakes and How to Avoid Them covers it

How deep it goes

Explains pool states, allocation, waiting, and four database limits, then contrasts HTTP idle and per-host limits.

Examples

Uses a five-connection database pool and 100 requests to one HTTP host to expose reuse and reconnection behavior.

What you can do after

Operate and configure database or HTTP pools by matching connection limits and idle policies to workload and backend capacity.

How it connects

Connects connection pooling with database capacity, goroutines, concurrent requests, HTTP clients, transports, timeouts, and latency.

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Also explained in

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  Python Concurrency with asyncioConnection pooling is the practice of maintaining reusable network connections so multiple operations can share them.
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  .NET in Action, Second EditionA connection pool is a managed collection of reusable network connections that limits and coordinates simultaneous access.
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  Rust Servers, Services, and AppsA connection pool is a managed collection of reusable database connections shared among clients or execution threads.
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  Logs and TelemetryConnection pooling is the practice of maintaining reusable database connections so operations can execute without repeatedly establishing new connections.
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  Elixir in Action, Third EditionA database connection pool is a bounded collection of reusable database connections managed to constrain simultaneous database operations.
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  Go by ExampleA connection pool is a managed collection of reusable network connections maintained to avoid repeatedly establishing new connections.
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  PostgreSQL Mistakes and How to Avoid ThemConnection pooling is a technique that reuses a bounded set of database connections to serve a larger number of client requests.
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  ASP.NET Core in Action, 3eConnection pooling is the reuse of established network connections across multiple client requests to reduce connection-setup overhead.

Compare how 9 books explain connection pooling →

Related concepts

• database connectionuses · A database connection is an active communication channel or session through which software sends operations to and receives results from a database system.
• connection poolerimplemented by · A connection pooler is software that maintains reusable database connections and assigns them to application requests as needed.

This explainer was generated by Manning's knowledge graph from the text of 100 Go Mistakes and How to Avoid Them. The section links point to the parts of the book it draws on.