---
title: "Latency"
description: "Latency is the time delay between initiating a request or operation and receiving its result — for example, the time from sending a database query to getting the first byte of its response back."
canonical: "https://motherduck.com/glossary/latency/"
related:
  - title: "DuckLake Lakehouse: Getting Started to Going Fast | MotherDuck"
    url: "https://motherduck.com/videos/ducklake-lakehouse-getting-started/"
  - title: "Glossary | MotherDuck Docs"
    url: "https://motherduck.com/docs/troubleshooting/glossary/"
  - title: "Perf is not enough"
    url: "https://motherduck.com/blog/perf-is-not-enough/"
gated_asset:
  title: "DuckLake on MotherDuck"
  url: "https://motherduck.com/product/ducklake/"
---

# Latency

> Latency is the time delay between initiating a request or operation and receiving its result — for example, the time from sending a database query to getting the first byte of its response back.

## Overview

Latency measures how long something takes from start to finish, typically expressed for a single operation (as opposed to throughput, which measures how much work completes over time). In distributed systems and databases, latency is usually reported as a distribution rather than a single number, because most systems have some fast requests and some slow ones — commonly summarized using percentiles like p50 (median), p95, and p99, since the tail of the distribution often matters more to user experience than the average.

## Components of latency

End-to-end latency for a database query, for instance, can include network round-trip time, connection setup, query planning/optimization, actual execution time, and time to serialize and transfer the result. Reducing latency typically means attacking whichever component dominates: caching to avoid repeated computation, indexing to avoid full scans, connection pooling to avoid repeated handshakes, or moving compute closer to data to cut network round trips.

## Measuring latency percentiles

```sql
SELECT
    quantile_cont(response_ms, [0.5, 0.95, 0.99]) AS latency_percentiles
FROM requests;
```

For very large request logs, `approx_quantile` gives a fast, bounded-error estimate of the same percentiles when exact computation is unnecessarily expensive.

## Latency versus throughput

Latency and throughput are related but distinct, and often in tension: a system can have low latency per request but low throughput if it can't handle many requests concurrently, or high throughput with high per-request latency if it processes requests in large batches. Query engines like DuckDB are generally optimized for low latency on interactive, single-query analytical workloads on one machine, since it executes queries using all available cores on the local hardware rather than distributing work across a cluster — which is also why very large, distributed workloads may favor a system built for high aggregate throughput across many nodes instead.