What is the HikariCP formula?

pool_size = (core_count × 2) + effective_spindle_count. For SSDs or NVMe drives use spindle_count = 1. For spinning-disk arrays use the actual number of physical spindles.

What is Little's Law?

Little's Law states L = λ × W, where L is the average number of items in the system, λ is the average arrival rate, and W is the average time spent in the system. Here L = required pool size, λ = peak concurrent requests/sec, W = average query duration in seconds.

Why not just set the pool size to a very large number?

Each idle connection consumes memory on both the application server and the database. Excess connections also increase context-switching overhead and can degrade throughput rather than improve it.

Should I use the HikariCP result or the Little's Law result?

Use the higher of the two as a starting point, then load-test and tune. The HikariCP formula is a hardware ceiling; Little's Law reflects real workload demand.

Do I need to multiply by the number of app servers?

Yes. The pool size calculated here is per application instance. If you run N instances, your database must support N × pool_size total connections.

Connection Pool Sizing Calculator

Name: Connection Pool Sizing Calculator
Availability: InStock
Author: Nham Vu

Calculate the optimal database connection pool size using the HikariCP formula and Little's Law analysis.

HikariCP Formula Inputs

CPU Core Count

Physical or virtual cores available to the database server.

Effective Spindle Count

Use 1 for SSD / NVMe. Use the number of physical spinning disks for HDD arrays.

Little's Law Inputs (optional)

Peak Concurrent Requests

Maximum number of requests hitting the database simultaneously.

Average Query Duration (ms)

Mean time a single query occupies a connection, in milliseconds.

Deployment Scale

Number of App Instances

How many application server instances share the database.

HikariCP Formula

pool = (cores × 2) + spindles

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Little's Law

L = concurrency × (query_ms / 1000)

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Enter Peak Concurrent Requests and Average Query Duration to enable.

Config Snippets

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