spark-instrumented-optimizer/docs/sql-ref-syntax-qry-explain.md

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Description

The EXPLAIN statement is used to provide logical/physical plans for an input statement. By default, this clause provides information about a physical plan only.

Syntax

{% highlight sql %} EXPLAIN [EXTENDED | CODEGEN | COST | FORMATTED] statement {% endhighlight %}

Parameters

EXTENDED

Generates parsed logical plan, analyzed logical plan, optimized logical plan and physical plan. Parsed Logical plan is a unresolved plan that extracted from the query. Analyzed logical plans transforms which translates unresolvedAttribute and unresolvedRelation into fully typed objects. The optimized logical plan transforms through a set of optimization rules, resulting in the physical plan.

CODEGEN

Generates code for the statement, if any and a physical plan.

COST

If plan node statistics are available, generates a logical plan and the statistics.

FORMATTED

Generates two sections: a physical plan outline and node details.

statement

Specifies a SQL statement to be explained.

Examples

{% highlight sql %}

--Default Output

EXPLAIN select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k; +----------------------------------------------------+ | plan | +----------------------------------------------------+ | == Physical Plan == *(2) HashAggregate(keys=[k#33], functions=[sum(cast(v#34 as bigint))]) +- Exchange hashpartitioning(k#33, 200), true, [id=#59] +- *(1) HashAggregate(keys=[k#33], functions=[partial_sum(cast(v#34 as bigint))]) +- *(1) LocalTableScan [k#33, v#34] | +----------------------------------------------------

-- Using Extended

EXPLAIN EXTENDED select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k; +----------------------------------------------------+ | plan | +----------------------------------------------------+ | == Parsed Logical Plan == 'Aggregate ['k], ['k, unresolvedalias('sum('v), None)] +- 'SubqueryAlias t +- 'UnresolvedInlineTable [k, v], [List(1, 2), List(1, 3)]

== Analyzed Logical Plan == k: int, sum(v): bigint Aggregate [k#47], [k#47, sum(cast(v#48 as bigint)) AS sum(v)#50L] +- SubqueryAlias t +- LocalRelation [k#47, v#48]

== Optimized Logical Plan == Aggregate [k#47], [k#47, sum(cast(v#48 as bigint)) AS sum(v)#50L] +- LocalRelation [k#47, v#48]

== Physical Plan == *(2) HashAggregate(keys=[k#47], functions=[sum(cast(v#48 as bigint))], output=[k#47, sum(v)#50L]) +- Exchange hashpartitioning(k#47, 200), true, [id=#79] +- *(1) HashAggregate(keys=[k#47], functions=[partial_sum(cast(v#48 as bigint))], output=[k#47, sum#52L]) +- *(1) LocalTableScan [k#47, v#48] | +----------------------------------------------------+

--Using Formatted

EXPLAIN FORMATTED select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k; +----------------------------------------------------+ | plan | +----------------------------------------------------+ | == Physical Plan ==

• HashAggregate (4) +- Exchange (3) +- * HashAggregate (2) +- * LocalTableScan (1)

(1) LocalTableScan [codegen id : 1] Output: [k#19, v#20]

(2) HashAggregate [codegen id : 1] Input: [k#19, v#20]

(3) Exchange Input: [k#19, sum#24L]

(4) HashAggregate [codegen id : 2] Input: [k#19, sum#24L] | +----------------------------------------------------+

{% endhighlight %}