1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
// SERVER-13946: When possible, place skip stages before fetch stages to avoid unnecessarily
// fetching documents that will be immediately discarded.
// The skip operation in a sharded query always occurs in the mongoS, so this test doesn't make
// sense on a sharded collection.
// @tags: [assumes_unsharded_collection, operations_longer_than_stepdown_interval_in_txns]
(function() {
"use strict";
load("jstests/libs/analyze_plan.js");
const coll = db.add_skip_stage_before_fetch;
coll.drop();
const testIndex = {
a: 1,
b: 1,
c: 1
};
assert.commandWorked(coll.createIndex(testIndex));
const bulk = coll.initializeUnorderedBulkOp();
for (let i = 0; i < 10000; i++) {
bulk.insert({
a: i % 2,
b: i % 4,
c: Math.floor(Math.random() * 1000),
d: Math.floor(Math.random() * 1000)
});
}
assert.commandWorked(bulk.execute());
// The {a: 0, b: 2} query will match exactly one quarter of the documents in the collection:
// 2500 in total. In the test queries below, we skip the first 2400, returning exactly 100
// documents.
// This find can be computed using the index, so we should only need to fetch the 100 documents
// that get returned to the client after skipping the first 2400.
let explainResult = coll.find({a: 0, b: 2}).hint(testIndex).skip(2400).explain("executionStats");
assert.gte(explainResult.executionStats.totalKeysExamined, 2500);
assert.eq(explainResult.executionStats.totalDocsExamined, 100);
// This sort can also be computed using the index.
explainResult =
coll.find({a: 0, b: 2}).hint(testIndex).sort({c: 1}).skip(2400).explain("executionStats");
assert.gte(explainResult.executionStats.totalKeysExamined, 2500);
assert.eq(explainResult.executionStats.totalDocsExamined, 100);
// This query is covered by the index, so there should be no fetch at all.
explainResult = coll.find({a: 0, b: 2}, {_id: 0, a: 1})
.hint(testIndex)
.sort({c: 1})
.skip(2400)
.explain("executionStats");
assert.gte(explainResult.executionStats.totalKeysExamined, 2500);
assert.eq(explainResult.executionStats.totalDocsExamined, 0);
assert(isIndexOnly(db, explainResult.queryPlanner.winningPlan));
// This sort requires a field that is not in the index, so we should be fetching all 2500
// documents that match the find predicate.
explainResult =
coll.find({a: 0, b: 2}).hint(testIndex).sort({d: 1}).skip(2400).explain("executionStats");
assert.gte(explainResult.executionStats.totalKeysExamined, 2500);
assert.eq(explainResult.executionStats.totalDocsExamined, 2500);
})();
|
