Description
for (let i = 0; i < 10000; i++) db.coll.insertOne({ a: ((Math.random() * 1000) | 0), b: ((Math.random() * 1000) | 0) });
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db.coll.createIndex({a:1})
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db.coll.createIndex({b:1})
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Then explain in Compass for a query like
{$or:[{a:200},{b:300}]}
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will result in a “Shard results differ” warning message in the explain output because the server performs two index scans using different indexes, even though sharding is not involved.