ANALYZE FORMAT=JSON is a mix of the EXPLAIN FORMAT=JSON and ANALYZE statement features. ANALYZE FORMAT=JSON $statement will execute $statement, and then print the output of EXPLAIN FORMAT=JSON, amended with the data from query execution.

Basic execution data

You can get the following also from tabular ANALYZE statement form:

  • r_rows is provided for any node that reads rows. It shows how many rows were read, on average
  • r_filtered is provided whenever there is a condition that is checked. It shows the percentage of rows left after checking the condition.

Advanced execution data

The most important data that is not available in tabula ANALYZE statement are:

  • r_loops field. This shows how many times the node was executed. Most query plan elements have this field.
  • r_total_time_ms field. It shows how much time in total was spent executing this node. If the node has subnodes, their execution time is included.
  • r_buffer_size field. Query plan nodes that make use of buffers report the size of buffer that was was used.

Data about individual query plan nodes

  • filesort node reports whether sorting was done with LIMIT n parameter, and how many rows were in the sort result.
  • block-nl-join node has r_loops field, which allows to tell whether Using join buffer was efficient
  • range-checked-for-each-record reports counters that show the result of the check.
  • expression-cache is used for subqueries, and it reports how many times the cache was used, and what cache hit ratio was.
  • union_result node has r_rows so one can see how many rows were produced after UNION operation
  • and so forth

Use cases

See Examples of ANALYZE FORMAT=JSON.

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