# Large datasets SnoutData is built to stay safe when you point it at very large tables. It watches for the queries that quietly read millions of rows, warns you before they run, and explains why. This is not an AI feature. The detection reads the database's own query plan and its indexes, so it is deterministic, instant, and offline, and it runs on every query. No model, no tokens, no guessing. Only the optional **Ask AI to fix** button (below) calls the assistant. ## Large scan warning Some queries look perfectly fine and still scan every row of a huge table. Wrapping an indexed column in a function is the classic trap: `WHERE DATE(created_at) = '2023-10-16'` cannot use the index on `created_at`, so the database falls back to a full table scan. Before SnoutData runs a query, it asks the database's own query planner how much it will read. If you are about to scan a large table with no usable index, it stops and tells you first, with the estimated row count.  You stay in control: choose **Run anyway** or **Cancel**. Nothing runs behind your back. ## Index and scan advice SnoutData flags the filters that defeat an index as you type them. A predicate like `DATE(col)`, `LOWER(col)`, a cast, or a leading-wildcard `LIKE '%term'` gets a marker in the editor with the reason and a suggested rewrite that keeps the index usable. After a query runs slowly, an advice strip appears above the results naming what made it slow (a full table scan, a sort with no index, a temporary table). Its **Ask AI to fix** button hands the statement to the [assistant](https://docs.snoutdata.com/ai-assistant/agentic) to propose an index or a rewrite. ## Long-running query warning While a query runs, the timer in the toolbar turns into a clear "taking longer than expected" warning once it passes a few seconds, so a runaway query is obvious. One click cancels it. ## Settings Tune the thresholds, or turn any of this off, under **Settings** in the **Large datasets** section: - **Warn before a large scan**, and the row estimate that triggers it. - **Warn a running query is slow after** a number of milliseconds (0 turns it off). - **Advise on index and scans** after a query takes a number of milliseconds (0 turns it off).