EXPLAIN

EXPLAIN 用于提供语句的执行计划。

Syntax

EXPLAIN [ANALYZE] SELECT ...

ANALYZE 子句将执行语句并测量每个计划节点花费的时间以及输出的总行数等。

示例

EXPLAIN SELECT * FROM monitor where host='host1';

| plan_type     | plan                                                                                                                                                                                                                                                         
| logical_plan  | Projection: monitor.host, monitor.ts, monitor.cpu, monitor.memory
  Filter: monitor.host = Utf8("host1")
    TableScan: monitor projection=[host, ts, cpu, memory], partial_filters=[monitor.host = Utf8("host1")]                                           |
| physical_plan | ProjectionExec: expr=[host@0 as host, ts@1 as ts, cpu@2 as cpu, memory@3 as memory]
  CoalesceBatchesExec: target_batch_size=4096
    FilterExec: host@0 = host1
      RepartitionExec: partitioning=RoundRobinBatch(10)
        ExecutionPlan(PlaceHolder)

plan_type 列指示了是 logical_plan 还是 physical_plan，plan 列详细说明了执行计划。

使用 ANALYZE 解释执行计划：

EXPLAIN ANALYZE SELECT * FROM monitor where host='host1';

| plan_type         | plan
| Plan with Metrics | CoalescePartitionsExec, metrics=[output_rows=1, elapsed_compute=79.167µs, spill_count=0, spilled_bytes=0, mem_used=0]
  ProjectionExec: expr=[host@0 as host, ts@1 as ts, cpu@2 as cpu, memory@3 as memory], metrics=[output_rows=1, elapsed_compute=17.176µs, spill_count=0, spilled_bytes=0, mem_used=0]
    CoalesceBatchesExec: target_batch_size=4096, metrics=[output_rows=1, elapsed_compute=14.248µs, spill_count=0, spilled_bytes=0, mem_used=0]
      CoalesceBatchesExec: target_batch_size=4096, metrics=[output_rows=1, elapsed_compute=17.21µs, spill_count=0, spilled_bytes=0, mem_used=0]
        FilterExec: host@0 = host1, metrics=[output_rows=1, elapsed_compute=541.801µs, spill_count=0, spilled_bytes=0, mem_used=0]
          CoalesceBatchesExec: target_batch_size=4096, metrics=[output_rows=3, elapsed_compute=43.004µs, spill_count=0, spilled_bytes=0, mem_used=0]
            RepartitionExec: partitioning=RoundRobinBatch(10), metrics=[fetch_time=5.832958ms, repart_time=10ns, send_time=2.467µs]
              RepartitionExec: partitioning=RoundRobinBatch(10), metrics=[fetch_time=386.585µs, repart_time=1ns, send_time=7.833µs]
                ExecutionPlan(PlaceHolder), metrics=[]