Find slow queries

Locate the queries that load the cluster most and decide which index or which model change fixes them.

Requirements

• A user with clusterMonitor and dbAdmin on the databases you review.

The ones running right now

db.currentOp({ secs_running: { $gte: 2 } });

The ones that load the most

db.getSiblingDB("admin").aggregate([
  { $queryStats: {} },
  { $sort: { "metrics.totalExecMicros.sum": -1 } },
  { $limit: 10 },
]);

Fix them

For each one, look at its plan with explain and create the index that covers its filter and its sort.

Check

After the change, the query drops in $queryStats and stops showing up in the profiler.

Common problems

• A slow query because of a key that always grows is not fixed with an index; read Keys and hotspots.

See also

• Query profiler
• Anti-patterns