Finding Queries With Multiple Plans In Query Store

Cached Out

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There are lots of examples of how to do this with the plan cache, but, well, the plan cache can be an awfully unstable place.

Query store being a bit more historically reliable, we can use some of the same tricks to track them down there too.

SELECT
    x.total_query_plans,
    qsq.query_hash,
    qsp.query_plan_hash,
    query_plan =
        TRY_CONVERT
        (
            xml,
            qsp.query_plan
        )
FROM 
(
    SELECT
        qsq.query_hash,
        distinct_query_plans = 
            COUNT_BIG(DISTINCT qsp.query_plan_hash),
        total_query_plans = 
            COUNT_BIG(qsp.query_plan_hash)
    FROM sys.query_store_query AS qsq
    JOIN sys.query_store_plan AS qsp
        ON qsq.query_id = qsp.query_id
    GROUP BY 
        qsq.query_hash
    HAVING  COUNT_BIG(DISTINCT qsp.query_plan_hash) > 1
    AND     COUNT_BIG(DISTINCT qsp.query_plan_hash)
                <= COUNT_BIG(qsp.query_plan_hash)
) AS x
CROSS APPLY
(
    SELECT TOP (x.total_query_plans)
        qsq.*
    FROM sys.query_store_query AS qsq
    WHERE x.query_hash = qsq.query_hash
) AS qsq
CROSS APPLY
(
    SELECT
        qsp.*
    FROM sys.query_store_plan AS qsp
    WHERE qsp.query_id = qsq.query_id
) AS qsp
ORDER BY 
    x.total_query_plans DESC;

Thanks for reading!

Going Further

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