Read a plan with explain

Use `explain` to see which index a query used, which ranges it touched and how much it read.

See how a query ran with explain: which index it used, which ranges it touched and how many documents it read to return the ones it returned.

Requirements

JavaScript

db.orders.find({ customer: "Ana Ruiz" }).sort({ created: -1 }).explain("executionStats");

Field	What it says
`winningPlan`	The chosen plan, with the index it uses.
`totalDocsExamined` against `nReturned`	If it reads many more documents than it returns, an index is missing.
TeselaDB's own stages	The ranges touched, the split, the merge of buckets and the spills.

After creating the missing index, totalDocsExamined drops until it gets close to nReturned in the same explain.

With the SBE engine, explain gives no slotBasedPlan; executionStages describes TeselaDB's plan.