Query plan information and structure

Depending on the query and database schema, EXPLAIN output includes the following information:.

Depending on the query and database schema, EXPLAIN output includes the following information:

  • Tables referenced by the statement

  • Estimated costs

  • Estimated row cardinality

  • Path ID, an integer that links to error messages and profiling counters so you troubleshoot performance issues more easily. For more information, see Profiling query plans.

  • Data operations such as SORT, FILTER, LIMIT, and GROUP BY

  • Projections used

  • Information about statistics—for example, whether they are current or out of range

  • Algorithms chosen for operations into the query, such as HASH/MERGE or GROUPBY HASH/GROUPBY PIPELINED

  • Data redistribution (broadcast, segmentation) across cluster nodes

Example

In the EXPLAIN output that follows, the optimizer processes a query in three steps, where each step identified by a unique path ID:

  • 0: Limit

  • 1: Sort

  • 2: Storage access and filter

In this section