在Spark SQL的执行过程中,QueryExecution类贯穿始终,它是Spark执行关系查询的主要workflow。 一条SQL执行过程 如上图所示,一条SQL在Spark SQL引擎的解析过程中被分为逻辑计划阶段和物理计划阶段。 在逻辑计划阶段,当Spark SQL引擎接收到一条SQL查询时,它首先将被解析为一个Unresolved Logical Plan。 此时的SQL解析树并...
Spark employs a query optimizer, called Catalyst, to interpret SQL queries to optimized query execution plans. Catalyst contains a number of optimization rules and supports cost-based optimization. Although query optimization techniques have been well studied in the field of relational database systems,...
buildIter总体估计大小超过spark.sql.autoBroadcastJoinThreshold设定的值,即不满足broadcast join条件 开启尝试使用hash join的开关,spark.sql.join.preferSortMergeJoin=false 每个分区的平均大小不超过spark.sql.autoBroadcastJoinThreshold设定的值,即shuffle read阶段每个分区 来自buildIter的记录要能放到内存中 streamIter...
My initial thought was that it's almost a constant operation (surely due to a local dataset) that wouldsomehowhave been optimized by Spark SQL and would give a result immediately, esp. the 1st one where Spark SQL is in full control of the query execution. Having had a look at the physi...
set of optimization rules to push down local-aggregates below all standard SQL operators. Derive local aggregates not only from group-by but also from semi-join and intersect. This allows Spark to aggregate data early and reduce the amount of data shuffled, a crit...
set of optimization rules to push down local-aggregates below all standard SQL operators. Derive local aggregates not only from group-by but also from semi-join and intersect. This allows Spark to aggregate data early and reduce the amount of data shuffl...
Over the years, there's been an extensive and continuous effort to improve Spark SQL's query optimizer and planner in order to generate high-quality query execution plans. One of the biggest improvements is the cost-based optimization framework that collects and leverages a variety of data statis...
query language:面向用户的查询语言接口,如 SQL、Streaming SQL、extensions jdbc driver SQL parser and validator query algebra to represent operations over data execution engine:calcite's operators (enumerable) 如下图,展示了 引用 Calcite 的软件,其中执行引擎部分,可以使用自己 Native 的引擎,或者外部其它系统...
If everything can be dynamically optimized, the physical optimization happens. Internals - AdaptiveSparkPlanExec What happens then during the physical execution? First, Apache Spark creates the initial version of the new plan from the starting physical plan. It does it increateQueryStages(plan:...
Next, go ahead and enable AQE by setting it to true with the following command:set spark.sql.adaptive.enabled = true;. In this section you'll run the same query provided in the previous section to measure performance of query execution time with AQE enabled. ...