mongo/jstests/aggregation/sources/collStats/query_exec_stats.js

// Test that queryExecStats within a $collStats stage returns the correct execution stats.
// @tags: [
//   assumes_no_implicit_collection_creation_after_drop,
//   does_not_support_repeated_reads,
// ]
import {assertErrorCode} from "jstests/aggregation/extras/utils.js";

const nDocs = 32;

const testDB = db.getSiblingDB("aggregation_query_exec_stats");
const coll = testDB.aggregation_query_exec_stats;
coll.drop();
assert.commandWorked(testDB.createCollection("aggregation_query_exec_stats", {capped: true, size: nDocs * 100}));

for (let i = 0; i < nDocs; i++) {
    assert.commandWorked(coll.insert({a: i}));
}

// Run a bunch of collection scans on the server.
for (let i = 0; i < nDocs; i++) {
    assert.eq(coll.find({a: i}).itcount(), 1);
}

// Test that an error is returned if queryExecStats is not an object.
let pipeline = [{$collStats: {queryExecStats: 1}}];
assertErrorCode(coll, pipeline, ErrorCodes.TypeMismatch, "queryExecStats spec must be an object");
pipeline = [{$collStats: {queryExecStats: "1"}}];
assertErrorCode(coll, pipeline, ErrorCodes.TypeMismatch, "queryExecStats spec must be an object");

// Test the accuracy of the result of queryExecStats as a standalone option.
pipeline = [{$collStats: {queryExecStats: {}}}];
let result = coll.aggregate(pipeline).next();
assert.eq(nDocs, result.queryExecStats.collectionScans.total);
assert.eq(nDocs, result.queryExecStats.collectionScans.nonTailable);

// Test tailable collection scans update collectionScans counters appropriately.
for (let i = 0; i < nDocs; i++) {
    assert.eq(coll.find({a: i}).tailable().itcount(), 1);
}
result = coll.aggregate(pipeline).next();
assert.eq(nDocs * 2, result.queryExecStats.collectionScans.total);
assert.eq(nDocs, result.queryExecStats.collectionScans.nonTailable);

// Run a query which will require the client to fetch multiple batches from the server. Ensure
// that the getMore commands don't increment the counter of collection scans.
assert.eq(coll.find({}).batchSize(2).itcount(), nDocs);
result = coll.aggregate(pipeline).next();
assert.eq(nDocs * 2 + 1, result.queryExecStats.collectionScans.total);
assert.eq(nDocs + 1, result.queryExecStats.collectionScans.nonTailable);

// Create index to test that index scans don't up the collection scan counter.
assert.commandWorked(coll.createIndex({a: 1}));
// Run a bunch of index scans.
for (let i = 0; i < nDocs; i++) {
    assert.eq(coll.find({a: i}).itcount(), 1);
}
result = coll.aggregate(pipeline).next();
// Assert that the number of collection scans hasn't increased.
assert.eq(nDocs * 2 + 1, result.queryExecStats.collectionScans.total);
assert.eq(nDocs + 1, result.queryExecStats.collectionScans.nonTailable);

// Test that we error when the collection does not exist.
coll.drop();
pipeline = [{$collStats: {queryExecStats: {}}}];
assertErrorCode(coll, pipeline, ErrorCodes.NamespaceNotFound);

// Test that we error when the database does not exist.
assert.commandWorked(testDB.dropDatabase());
assertErrorCode(coll, pipeline, ErrorCodes.NamespaceNotFound);