A Presto query in watsonx.data is running significantly slower than expected on an Iceberg table. Which diagnostic step should be taken first?

EXPLAIN output reveals the query execution plan — including partition pruning effectiveness; join strategies; and estimated row counts — allowing identification of performance bottlenecks like missing statistics or inefficient joins. The incorrect options ("Increase the storage bucket's replication factor", "Restart the Presto coordinator to clear query cache", "Convert the table from Iceberg to Delta Lake format") are distractors that don't fully capture the concept described.