53 lines
2.1 KiB
JavaScript
53 lines
2.1 KiB
JavaScript
// From the work done for SERVER-22093, an aggregation pipeline that does not require any fields
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// from the input documents will tell the query planner to use a count scan, which is faster than an
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// index scan. In this test file, we check this behavior through explain().
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//
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// Cannot implicitly shard accessed collections because the explain output from a mongod when run
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// against a sharded collection is wrapped in a "shards" object with keys for each shard.
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//
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// This test assumes that an initial $match will be absorbed by the query system, which will not
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// happen if the $match is wrapped within a $facet stage.
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// @tags: [do_not_wrap_aggregations_in_facets,assumes_unsharded_collection]
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load('jstests/libs/analyze_plan.js');
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(function() {
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"use strict";
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var coll = db.countscan;
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coll.drop();
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for (var i = 0; i < 3; i++) {
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for (var j = 0; j < 10; j += 2) {
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coll.insert({foo: i, bar: j});
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}
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}
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coll.ensureIndex({foo: 1});
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var simpleGroup = coll.aggregate([{$group: {_id: null, count: {$sum: 1}}}]).toArray();
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assert.eq(simpleGroup.length, 1);
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assert.eq(simpleGroup[0]["count"], 15);
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var explained =
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coll.explain().aggregate([{$match: {foo: {$gt: 0}}}, {$group: {_id: null, count: {$sum: 1}}}]);
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assert(planHasStage(db, explained.stages[0].$cursor.queryPlanner.winningPlan, "COUNT_SCAN"));
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explained = coll.explain().aggregate([
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{$match: {foo: {$gt: 0}}},
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{$project: {_id: 0, a: {$literal: null}}},
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{$group: {_id: null, count: {$sum: 1}}}
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]);
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assert(planHasStage(db, explained.stages[0].$cursor.queryPlanner.winningPlan, "COUNT_SCAN"));
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// Make sure a $count stage can use the COUNT_SCAN optimization.
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explained = coll.explain().aggregate([{$match: {foo: {$gt: 0}}}, {$count: "count"}]);
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assert(planHasStage(db, explained.stages[0].$cursor.queryPlanner.winningPlan, "COUNT_SCAN"));
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// A $match that is not a single range cannot use the COUNT_SCAN optimization.
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explained = coll.explain().aggregate([{$match: {foo: {$in: [0, 1]}}}, {$count: "count"}]);
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assert(!planHasStage(db, explained.stages[0].$cursor.queryPlanner.winningPlan, "COUNT_SCAN"));
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}());
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