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// @tags: [requires_getmore, assumes_balancer_off]
// Test subtleties of batchSize and limit.
(function() {
"use strict";
load("jstests/libs/fixture_helpers.js"); // For FixtureHelpers.
var t = db.jstests_batch_size;
t.drop();
for (var i = 0; i < 4; i++) {
t.save({_id: i, a: i});
}
function runIndexedTests() {
// With limit, indexed.
assert.eq(2, t.find().limit(2).itcount());
assert.eq(2, t.find().sort({a: 1}).limit(2).itcount());
// With batchSize, indexed.
// SERVER-12438: If there is an index that provides the sort, then a plan with an unindexed
// sort should never be used. Consequently, batchSize will NOT be a hard limit in this
// case. WARNING: the behavior described above may change in the future.
assert.eq(4, t.find().batchSize(2).itcount());
assert.eq(4, t.find().sort({a: 1}).batchSize(2).itcount());
}
// Without batch size or limit, unindexed.
assert.eq(4, t.find().itcount());
assert.eq(4, t.find().sort({a: 1}).itcount());
// With limit, unindexed.
assert.eq(2, t.find().limit(2).itcount());
assert.eq(2, t.find().sort({a: 1}).limit(2).itcount());
assert.eq(4, t.find().batchSize(2).itcount());
assert.eq(4, t.find().sort({a: 1}).batchSize(2).itcount());
// With negative batchSize. A negative batchSize value instructs the server
// to return just a single batch of results.
assert.eq(1, t.find().batchSize(-1).itcount());
assert.eq(2, t.find().batchSize(-2).itcount());
// Run the tests with the index twice in order to double check plan caching.
t.ensureIndex({a: 1});
for (var i = 0; i < 2; i++) {
runIndexedTests();
}
// The next tests make sure that we obey limit and batchSize properly when the sort could be
// either indexed or unindexed.
t.drop();
t.ensureIndex({a: 1});
t.ensureIndex({b: 1});
for (var i = 0; i < 100; i++) {
t.save({_id: i, a: i, b: 1});
}
// Without a hint. Do it twice to make sure caching is ok.
for (var i = 0; i < 2; i++) {
assert.eq(15, t.find({a: {$gte: 85}}).sort({b: 1}).batchSize(2).itcount());
assert.eq(6, t.find({a: {$gte: 85}}).sort({b: 1}).limit(6).itcount());
}
// Hinting 'a'.
assert.eq(15, t.find({a: {$gte: 85}}).sort({b: 1}).hint({a: 1}).batchSize(2).itcount());
assert.eq(6, t.find({a: {$gte: 85}}).sort({b: 1}).hint({a: 1}).limit(6).itcount());
// Hinting 'b'.
assert.eq(15, t.find({a: {$gte: 85}}).sort({b: 1}).hint({b: 1}).batchSize(2).itcount());
assert.eq(6, t.find({a: {$gte: 85}}).sort({b: 1}).hint({b: 1}).limit(6).itcount());
// With explain.
var explain = t.find({a: {$gte: 85}}).sort({b: 1}).batchSize(2).explain("executionStats");
assert.eq(15, explain.executionStats.nReturned);
explain = t.find({a: {$gte: 85}}).sort({b: 1}).limit(6).explain("executionStats");
if (FixtureHelpers.isMongos(db)) {
// If we're talking to a mongos, we expect at most one batch from each shard.
assert.eq(FixtureHelpers.numberOfShardsForCollection(t) * 6, explain.executionStats.nReturned);
} else {
assert.eq(6, explain.executionStats.nReturned);
}
// Double check that we're not scanning more stuff than we have to. In order to get the sort
// using index 'a', we should need to scan about 50 keys and 50 documents.
var explain = t.find({a: {$gte: 50}}).sort({b: 1}).hint({a: 1}).limit(6).explain("executionStats");
assert.lte(explain.executionStats.totalKeysExamined, 60);
assert.lte(explain.executionStats.totalDocsExamined, 60);
if (FixtureHelpers.isMongos(db)) {
// If we're talking to a mongos, we expect at most one batch from each shard.
assert.eq(FixtureHelpers.numberOfShardsForCollection(t) * 6, explain.executionStats.nReturned);
} else {
assert.eq(6, explain.executionStats.nReturned);
}
// -------
// During plan ranking, we treat ntoreturn as a limit. This prevents us from buffering too much
// data in a blocking sort stage during plan ranking.
t.drop();
// Generate big string to use in the object - 1MB+ String
var bigStr = "ABCDEFGHIJKLMNBOPQRSTUVWXYZ012345687890";
while (bigStr.length < 1000000) {
bigStr = bigStr + "::" + bigStr;
}
// Insert enough documents to exceed the 32 MB in-memory sort limit.
const nDocs = 40 * FixtureHelpers.numberOfShardsForCollection(t);
for (var i = 0; i < nDocs; i++) {
var doc = {x: 1, y: 1, z: i, big: bigStr};
t.insert(doc);
}
// Two indices needed in order to trigger plan ranking. Neither index provides the sort order.
t.ensureIndex({x: 1});
t.ensureIndex({y: 1});
// We should only buffer 3 docs in memory.
var cursor = t.find({x: 1, y: 1}).sort({z: -1}).limit(3);
assert.eq(nDocs - 1, cursor.next().z);
assert.eq(nDocs - 2, cursor.next().z);
assert.eq(nDocs - 3, cursor.next().z);
assert(!cursor.hasNext());
}());
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