# How BigQuery uses replay testing

Before BigQuery introduces system updates, it tests a sample of user
queries to check for regressions by re-running queries from production
workloads. These background tests can help detect system updates that might
compromise the accuracy or performance of existing user queries.

To achieve comprehensive coverage, BigQuery automatically selects
a diverse, representative subset of queries from production workloads. If the
validation detects regressions, BigQuery doesn't implement the
update.

This automated validation respects data privacy. BigQuery re-runs
the queries in the background without modifying your data, and the tests incur
no additional cost or resource consumption. Data access logs might attribute
these re-executions to the `bigquery-adminbot@system.gserviceaccount.com`
account.

## What's next

- Learn how to [run queries](https://docs.cloud.google.com/bigquery/docs/running-queries).
- Learn about [SQL in BigQuery](https://docs.cloud.google.com/bigquery/docs/introduction-sql).