Ahrefs, a renowned web analytics company, has successfully transitioned to using ClickHouse for its massive data storage needs. Founded in 2010, Ahrefs processes immense volumes of web analytics data and has the world's largest index of live backlinks. Initially, they used custom solutions like Cassandra and Hypertable, but found them inadequate due to limitations such as inflexible query engines and scaling challenges. In 2019, they discovered ClickHouse, which offered superior performance, a SQL interface, and versatile I/O support, making it an ideal choice for their growing datasets. Ahrefs has since embedded ClickHouse deeply into its system, operating multiple clusters on hardware with hundreds of hosts, including geo-replicated main cluster for redundancy and task-specific efficiency. To handle large-scale data insertions, they use buffering techniques and extensive fetch and attach commands to move data efficiently across servers. They have also developed internal monitoring tools like the "Birdseye View Tool" and "Query Analyzer" to optimize query performance. Furthermore, Ahrefs contributed a solution for mark compression in ClickHouse, which eliminated the need for mutexes and reduced memory consumption by three to six times. The transition to ClickHouse has brought significant improvements in data handling and performance, allowing Ahrefs to manage massive data volumes more efficiently, while also enhancing query performance and saving time.