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    Finding Expensive Queries By Memory Usage

    Identifying Expensive Queries by Memory Usage in ClickHouse

    Learn how to use the `system.query_log` table to find the most memory-intensive queries in ClickHouse, with examples for clustered and standalone setups.

    Using the system.query_log table​

    The following useful query shows which of your executed queries used the most memory.

    A couple of comments about this query:

    • the results are computed from the past day (now() - toIntervalDay(1))) but you can easily modify the time interval
    • it assumes you have a cluster named default, which is the name of your cluster in ClickHouse Cloud. Change default to the name of your cluster
    • if you do not have a cluster, see the query listed at the end of this article

    The response looks like:

    Note

    If you do not have a system.query_log table, then you likely do not have query logging enabled. View the details of the query_log setting for details on how to enable it.

    If you do not have a cluster, use can just query your one system.query_log table directly:

    · 2 min read