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Adaptive workload manager

The adaptive workload manager automatically controls the admission of queries for execution to ensure that concurrently executing queries do not overwhelm the available resources.

Running several queries1 simultaneously can lead to resource competition that, if left unmanaged, can result in system overload and query failure. The database employs an adaptive workload manager that controls admission of queries for execution, based on available resources.

Whether a query is allowed to run depends only on its resource requirements and the resources that are available. There is no fixed limit to the number of queries that can run concurrently. If a query is submitted to the database server but there are insufficient resources available to run the query, it is queued. The query is later admitted for execution, when resources become available.

The adaptive workload manager automatically adjusts the workload to run the optimal number of queries while maintaining stability of the database and avoiding errors. It also uses a combination of both latency-sensitive and resource-based job scheduling to ensure reliable throughput (that is, it tries to ensure that small queries are not held up by larger queries while still ensuring fairness across different classes of queries).

1 For simplicity, the term "query" is used to refer to the statements controlled by the adaptive workload manager, even though it controls both SELECT statements (queries) and INSERT statements. The adaptive workload manager does not control CALL statements.