When developing code that involves connecting to databases, you may come across a term called DB pools.
Let’s understand it.
What is a DB Pool?
It is basically a reusable collection of open connections to a database.
Instead of creating a new connection every time you run a query, the pool keeps several connections open so they can be reused instantly.
The reason connection pools exist
Opening a new DB connection is slow and expensive because it involves a number of things like:
- Authenticating
- Allocating memory
- Starting a session
- Sending startup packets
Key concepts of a connection pool
Maximum connections: The maximum number of connections that will ever be open.
Idle connections: Connections that are unused but open; they are ready to serve new work instantly.
Borrow and Return
- When an application needs a connection, it borrows one from the pool.
- After that, it will run the queries and return it to the pool.
Connection Lifetime: Pools set rules to close connections after a specified period of time, recreate them if the DB restarts, etc.
Concurrency: Multiple threads or requests can use different connections simultaneously, as long as the pool has capacity.
Backpressure
- There can be cases where all connections are busy.
- In such cases, new requests wait until a connection is free or time out if they wait too long.
- This prevents flooding the database with too many connections.
What happens when connection pools are not used
Without a pool, every request creates a new connection.
And your DB will end up facing a situation like
- 1000 connections opened
- Postgres starts rejecting new ones with “too many clients”
- Your server may slow down or crash because it cannot get a connection
- The whole system becomes unstable
With the pool, we have rules set in place to prevent such collapses. For eg:
- Max 20 connections
- All reused
- Helps the System stays more stable
Wrapping up
Hope you got an idea of why pools are so essential when developing software, and how various situations are handled with pools.
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