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Database Connection Pool Calculator

Size a database connection pool from throughput, query time and instance count.

About Database Connection Pool Calculator

Required concurrency follows from throughput multiplied by query duration, then divides across instances. Total connections scale with instance count, which is what makes horizontal scaling exhaust the database limit. Oversized pools hurt rather than help, because a database serving more concurrent queries than it has cores spends the difference on context switching.

Formula

Database Connection Pool

Concurrency = requests per second × query time, which is Little's Law

pool size
Connections held open per application instance
connection limit
Hard cap on the database server, shared across all clients

Worked example

With the default values below, Database Connection Pool Calculator returns Pool Size per Instance of 4. Change any input above and every figure here is recalculated in your browser.

Inputs used

Requests per secondminimum 0
800
Average query timeminimum 0.1 ms
12 ms
Application instancesminimum 1
4
Database connection limitminimum 1
100
Headroom for spikesaccepts 0–200 %
30 %

Results

Pool Size per Instance
4
Concurrent Queries Required
9.60
Total Connections Across Instances
16
Share of the Database Limit Used
16.00%
Verdict
Pool size is reasonable for this workload

Step by step

  1. 1Values used
  2. 2Database Connection Pool
  3. 3Pool Size per Instance= 4
  4. 4Concurrent Queries Required= 9.60
  5. 5Total Connections Across Instances= 16
  6. 6Share of the Database Limit Used= 16.00
  7. 7Verdict= Pool size is reasonable for this workload

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Database Connection Pool calculated?

Concurrency = requests per second × query time, which is Little's Law Required concurrency follows from throughput multiplied by query duration, then divides across instances. Total connections scale with instance count, which is what makes horizontal scaling exhaust the database limit.

Why does Database Connection Pool matter?

Oversized pools hurt rather than help, because a database serving more concurrent queries than it has cores spends the difference on context switching.

What values do I need to enter?

This calculator takes 5 inputs: Requests per second, Average query time, Application instances, Database connection limit, Headroom for spikes. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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