> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vortexiq.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Top 10 Slowest Queries, ClickHouse

> Top 10 Slowest Queries for ClickHouse instances. Tracked live in Vortex IQ Nerve Centre. How to read it, why it matters, and how to act on it.

**Card class:** [Non-Hero](/nerve-centre/overview#card-classes-explained)  •  **Category:** [Performance](/nerve-centre/connectors#connectors-by-type)

## At a glance

> **Top 10 Slowest Queries** ranks the ten longest-running queries seen over the last 24 hours, one query per row. It is the "where is the time going" view: instead of an aggregate latency number, it names the specific queries that are eating CPU, memory, and read bandwidth so a DBA can target the worst offenders directly. The table typically carries the query text (or its normalised hash), duration, rows read, and memory used.

## What it tracks

The card reads from `system.query_log`, the table that records one row per completed query with its `query_duration_ms`, `read_rows`, `read_bytes`, `memory_usage`, and `normalized_query_hash`. Over a 24h window it orders by `query_duration_ms` descending and returns the top ten, broken down by row. These are the queries that dominate your instance: a single full-scan aggregation over a billion-row table, a missing `PREWHERE` filter, or a join that fans out far wider than expected. Grouping by `normalized_query_hash` shows when one query shape recurs and is collectively the heaviest, which matters more than a one-off heavy ad-hoc query. The card carries no alert threshold of its own; it is the diagnostic detail you open when [Slow-Query Rate %](/nerve-centre/kpi-cards/clickhouse/slow-query-rate) or [Query Latency p99 (ms)](/nerve-centre/kpi-cards/clickhouse/query-latency-p99-ms) moves, to see exactly which statements are responsible.

## Reconciling against the source

Confirm the ranking directly in `clickhouse-client` with `SELECT query_duration_ms, read_rows, memory_usage, query FROM system.query_log WHERE type = 'QueryFinish' AND event_time > now() - INTERVAL 24 HOUR ORDER BY query_duration_ms DESC LIMIT 10`. On ClickHouse Cloud the same query runs in the SQL console, and the managed service also exposes a query-insights view that ranks the heaviest query shapes over time.

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### Tracked live in Vortex IQ Nerve Centre

*Top 10 Slowest Queries* is one of hundreds of KPI pulses Vortex IQ tracks across ClickHouse and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English.

[Start for free](https://app.vortexiq.ai/login) or [book a demo](https://www.vortexiq.ai/contact-us) to see this metric running on your own data.