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mediumSystem Design

What is database connection pooling?

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01

Understand the problem

Explain connection pools.

connection-pool
02

Attempt it yourself

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Nudge consolestandby

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03

Study the solution

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Use cases

We'll scope the problem to handle only the following use cases

  • User needs to understand connection-pool to make architecture d

Solution ready — 2 min read

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04

Read the code

A pool of N reusable connections
Run Playground
import threading, queue, time

class Pool:
    def __init__(self, size):
        self.free = queue.Queue()
        for i in range(size):
            self.free.put("conn-" + str(i))   # pre-open N connections
    def acquire(self):
        return self.free.get()                 # blocks/queues if none free
    def release(self, conn):
        self.free.put(conn)

pool = Pool(2)                                  # only 2 connections for everyone

def handle(req):
    conn = pool.acquire()
    print(req, "using", conn)
    time.sleep(0.05)                            # run query
    pool.release(conn)                          # return -> reused

threads = [threading.Thread(target=handle, args=("req" + str(i),)) for i in range(5)]
for t in threads: t.start()
for t in threads: t.join()
print("5 requests served by 2 pooled connections")
05

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