summaryrefslogtreecommitdiff
path: root/src/mongo/db/query/planner_ixselect.cpp
blob: f883b5468be51b6def18434dba307948d180e753 (plain)
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
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
/**
 *    Copyright (C) 2014 MongoDB Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery

#include "mongo/db/query/planner_ixselect.h"

#include <vector>

#include "mongo/db/geo/hash.h"
#include "mongo/db/index_names.h"
#include "mongo/db/matcher/expression_array.h"
#include "mongo/db/matcher/expression_geo.h"
#include "mongo/db/matcher/expression_text.h"
#include "mongo/db/query/indexability.h"
#include "mongo/db/query/index_tag.h"
#include "mongo/db/query/query_planner_common.h"
#include "mongo/util/log.h"

namespace mongo {

    static double fieldWithDefault(const BSONObj& infoObj, const string& name, double def) {
        BSONElement e = infoObj[name];
        if (e.isNumber()) { return e.numberDouble(); }
        return def;
    }

    /**
     * 2d indices don't handle wrapping so we can't use them for queries that wrap.
     */
    static bool twoDWontWrap(const Circle& circle, const IndexEntry& index) {

        GeoHashConverter::Parameters hashParams;
        Status paramStatus = GeoHashConverter::parseParameters(index.infoObj, &hashParams);
        verify(paramStatus.isOK()); // we validated the params on index creation

        GeoHashConverter conv(hashParams);

        // FYI: old code used flat not spherical error.
        double yscandist = rad2deg(circle.radius) + conv.getErrorSphere();
        double xscandist = computeXScanDistance(circle.center.y, yscandist);
        bool ret = circle.center.x + xscandist < 180
                && circle.center.x - xscandist > -180
                && circle.center.y + yscandist < 90
                && circle.center.y - yscandist > -90;
        return ret;
    }

    // static
    void QueryPlannerIXSelect::getFields(const MatchExpression* node,
                                         string prefix,
                                         unordered_set<string>* out) {
        // Do not traverse tree beyond a NOR negation node
        MatchExpression::MatchType exprtype = node->matchType();
        if (exprtype == MatchExpression::NOR) {
            return;
        }

        // Leaf nodes with a path and some array operators.
        if (Indexability::nodeCanUseIndexOnOwnField(node)) {
            out->insert(prefix + node->path().toString());
        }
        else if (Indexability::arrayUsesIndexOnChildren(node)) {
            // If the array uses an index on its children, it's something like
            // {foo : {$elemMatch: { bar: 1}}}, in which case the predicate is really over
            // foo.bar.
            //
            // When we have {foo: {$all: [{$elemMatch: {a:1}}], the path of the embedded elemMatch
            // is empty.  We don't want to append a dot in that case as the field would be foo..a.
            if (!node->path().empty()) {
                prefix += node->path().toString() + ".";
            }

            for (size_t i = 0; i < node->numChildren(); ++i) {
                getFields(node->getChild(i), prefix, out);
            }
        }
        else if (node->isLogical()) {
            for (size_t i = 0; i < node->numChildren(); ++i) {
                getFields(node->getChild(i), prefix, out);
            }
        }
    }

    // static
    void QueryPlannerIXSelect::findRelevantIndices(const unordered_set<string>& fields,
                                                   const vector<IndexEntry>& allIndices,
                                                   vector<IndexEntry>* out) {
        for (size_t i = 0; i < allIndices.size(); ++i) {
            BSONObjIterator it(allIndices[i].keyPattern);
            verify(it.more());
            BSONElement elt = it.next();
            if (fields.end() != fields.find(elt.fieldName())) {
                out->push_back(allIndices[i]);
            }
        }
    }

    // static
    bool QueryPlannerIXSelect::compatible(const BSONElement& elt,
                                          const IndexEntry& index,
                                          MatchExpression* node) {
        // Historically one could create indices with any particular value for the index spec,
        // including values that now indicate a special index.  As such we have to make sure the
        // index type wasn't overridden before we pay attention to the string in the index key
        // pattern element.
        //
        // e.g. long ago we could have created an index {a: "2dsphere"} and it would
        // be treated as a btree index by an ancient version of MongoDB.  To try to run
        // 2dsphere queries over it would be folly.
        string indexedFieldType;
        if (String != elt.type() || (INDEX_BTREE == index.type)) {
            indexedFieldType = "";
        }
        else {
            indexedFieldType = elt.String();
        }

        // We know elt.fieldname() == node->path().
        MatchExpression::MatchType exprtype = node->matchType();

        if (indexedFieldType.empty()) {
            // Can't check for null w/a sparse index.
            if (exprtype == MatchExpression::EQ && index.sparse) {
                const EqualityMatchExpression* expr
                    = static_cast<const EqualityMatchExpression*>(node);
                if (expr->getData().isNull()) {
                    return false;
                }
            }

            // Can't check for $in w/ null element w/a sparse index.
            if (exprtype == MatchExpression::MATCH_IN && index.sparse) {
                const InMatchExpression* expr = static_cast<const InMatchExpression*>(node);
                if (expr->getData().hasNull()) {
                    return false;
                }
            }

            // We can't use a btree-indexed field for geo expressions.
            if (exprtype == MatchExpression::GEO || exprtype == MatchExpression::GEO_NEAR) {
                return false;
            }

            // There are restrictions on when we can use the index if
            // the expression is a NOT.
            if (exprtype == MatchExpression::NOT) {
                // Don't allow indexed NOT on special index types such as geo or text indices.
                if (INDEX_BTREE != index.type) {
                    return false;
                }

                // Prevent negated preds from using sparse indices. Doing so would cause us to
                // miss documents which do not contain the indexed fields.
                if (index.sparse) {
                    return false;
                }

                // Can't index negations of MOD, REGEX, TYPE_OPERATOR, or ELEM_MATCH_VALUE.
                MatchExpression::MatchType childtype = node->getChild(0)->matchType();
                if (MatchExpression::REGEX == childtype ||
                    MatchExpression::MOD == childtype ||
                    MatchExpression::TYPE_OPERATOR == childtype ||
                    MatchExpression::ELEM_MATCH_VALUE == childtype) {
                    return false;
                }

                // If it's a negated $in, it can't have any REGEX's inside.
                if (MatchExpression::MATCH_IN == childtype) {
                    InMatchExpression* ime = static_cast<InMatchExpression*>(node->getChild(0));
                    if (ime->getData().numRegexes() != 0) {
                        return false;
                    }
                }
            }

            // We can only index EQ using text indices.  This is an artificial limitation imposed by
            // FTSSpec::getIndexPrefix() which will fail if there is not an EQ predicate on each
            // index prefix field of the text index.
            //
            // Example for key pattern {a: 1, b: "text"}:
            // - Allowed: node = {a: 7}
            // - Not allowed: node = {a: {$gt: 7}}

            if (INDEX_TEXT != index.type) {
                return true;
            }

            // If we're here we know it's a text index.  Equalities are OK anywhere in a text index.
            if (MatchExpression::EQ == exprtype) {
                return true;
            }

            // Not-equalities can only go in a suffix field of an index kp.  We look through the key
            // pattern to see if the field we're looking at now appears as a prefix.  If so, we
            // can't use this index for it.
            BSONObjIterator specIt(index.keyPattern);
            while (specIt.more()) {
                BSONElement elt = specIt.next();
                // We hit the dividing mark between prefix and suffix, so whatever field we're
                // looking at is a suffix, since it appears *after* the dividing mark between the
                // two.  As such, we can use the index.
                if (String == elt.type()) {
                    return true;
                }

                // If we're here, we're still looking at prefix elements.  We know that exprtype
                // isn't EQ so we can't use this index.
                if (node->path() == elt.fieldNameStringData()) {
                    return false;
                }
            }

            // NOTE: This shouldn't be reached.  Text index implies there is a separator implies we
            // will always hit the 'return true' above.
            invariant(0);
            return true;
        }
        else if (IndexNames::HASHED == indexedFieldType) {
            return exprtype == MatchExpression::MATCH_IN || exprtype == MatchExpression::EQ;
        }
        else if (IndexNames::GEO_2DSPHERE == indexedFieldType) {
            if (exprtype == MatchExpression::GEO) {
                // within or intersect.
                GeoMatchExpression* gme = static_cast<GeoMatchExpression*>(node);
                const GeoExpression& gq = gme->getGeoExpression();
                const GeometryContainer& gc = gq.getGeometry();
                return gc.hasS2Region();
            }
            else if (exprtype == MatchExpression::GEO_NEAR) {
                GeoNearMatchExpression* gnme = static_cast<GeoNearMatchExpression*>(node);
                // Make sure the near query is compatible with 2dsphere.
                return gnme->getData().centroid->crs == SPHERE;
            }
            return false;
        }
        else if (IndexNames::GEO_2D == indexedFieldType) {
            if (exprtype == MatchExpression::GEO_NEAR) {
                GeoNearMatchExpression* gnme = static_cast<GeoNearMatchExpression*>(node);
                // Make sure the near query is compatible with 2d index
                return gnme->getData().centroid->crs == FLAT || !gnme->getData().isWrappingQuery;
            }
            else if (exprtype == MatchExpression::GEO) {
                // 2d only supports within.
                GeoMatchExpression* gme = static_cast<GeoMatchExpression*>(node);
                const GeoExpression& gq = gme->getGeoExpression();
                if (GeoExpression::WITHIN != gq.getPred()) {
                    return false;
                }

                const GeometryContainer& gc = gq.getGeometry();

                // 2d indices require an R2 covering
                if (gc.hasR2Region()) {
                    return true;
                }

                const CapWithCRS* cap = gc.getCapGeometryHack();

                // 2d indices can answer centerSphere queries.
                if (NULL == cap) {
                    return false;
                }

                verify(SPHERE == cap->crs);
                const Circle& circle = cap->circle;

                // No wrapping around the edge of the world is allowed in 2d centerSphere.
                return twoDWontWrap(circle, index);
            }
            return false;
        }
        else if (IndexNames::TEXT == indexedFieldType) {
            return (exprtype == MatchExpression::TEXT);
        }
        else if (IndexNames::GEO_HAYSTACK == indexedFieldType) {
            return false;
        }
        else {
            warning() << "Unknown indexing for node " << node->toString()
                      << " and field " << elt.toString() << endl;
            verify(0);
        }
    }

    // static
    void QueryPlannerIXSelect::rateIndices(MatchExpression* node,
                                           string prefix,
                                           const vector<IndexEntry>& indices) {
        // Do not traverse tree beyond logical NOR node
        MatchExpression::MatchType exprtype = node->matchType();
        if (exprtype == MatchExpression::NOR) {
            return;
        }

        // Every indexable node is tagged even when no compatible index is
        // available.
        if (Indexability::isBoundsGenerating(node)) {
            string fullPath;
            if (MatchExpression::NOT == node->matchType()) {
                fullPath = prefix + node->getChild(0)->path().toString();
            }
            else {
                fullPath = prefix + node->path().toString();
            }

            verify(NULL == node->getTag());
            RelevantTag* rt = new RelevantTag();
            node->setTag(rt);
            rt->path = fullPath;

            // TODO: This is slow, with all the string compares.
            for (size_t i = 0; i < indices.size(); ++i) {
                BSONObjIterator it(indices[i].keyPattern);
                BSONElement elt = it.next();
                if (elt.fieldName() == fullPath && compatible(elt, indices[i], node)) {
                    rt->first.push_back(i);
                }
                while (it.more()) {
                    elt = it.next();
                    if (elt.fieldName() == fullPath && compatible(elt, indices[i], node)) {
                        rt->notFirst.push_back(i);
                    }
                }
            }

            // If this is a NOT, we have to clone the tag and attach
            // it to the NOT's child.
            if (MatchExpression::NOT == node->matchType()) {
                RelevantTag* childRt = static_cast<RelevantTag*>(rt->clone());
                childRt->path = rt->path;
                node->getChild(0)->setTag(childRt);
            }
        }
        else if (Indexability::arrayUsesIndexOnChildren(node)) {
            // See comment in getFields about all/elemMatch and paths.
            if (!node->path().empty()) {
                prefix += node->path().toString() + ".";
            }
            for (size_t i = 0; i < node->numChildren(); ++i) {
                rateIndices(node->getChild(i), prefix, indices);
            }
        }
        else if (node->isLogical()) {
            for (size_t i = 0; i < node->numChildren(); ++i) {
                rateIndices(node->getChild(i), prefix, indices);
            }
        }
    }

    // static
    void QueryPlannerIXSelect::stripInvalidAssignments(MatchExpression* node,
                                                       const vector<IndexEntry>& indices) {

        stripInvalidAssignmentsToTextIndexes(node, indices);

        if (MatchExpression::GEO != node->matchType() &&
            MatchExpression::GEO_NEAR != node->matchType()) {

            stripInvalidAssignmentsTo2dsphereIndices(node, indices);
        }
    }

    namespace {

        /**
         * For every node in the subtree rooted at 'node' that has a RelevantTag, removes index
         * assignments from that tag.
         *
         * Used as a helper for stripUnneededAssignments().
         */
        void clearAssignments(MatchExpression* node) {
            if (node->getTag()) {
                RelevantTag* rt = static_cast<RelevantTag*>(node->getTag());
                rt->first.clear();
                rt->notFirst.clear();
            }

            for (size_t i = 0; i < node->numChildren(); i++) {
                clearAssignments(node->getChild(i));
            }
        }

    } // namespace

    // static
    void QueryPlannerIXSelect::stripUnneededAssignments(MatchExpression* node,
                                                        const std::vector<IndexEntry>& indices) {
        if (MatchExpression::AND == node->matchType()) {
            for (size_t i = 0; i < node->numChildren(); i++) {
                MatchExpression* child = node->getChild(i);

                if (MatchExpression::EQ != child->matchType()) {
                    continue;
                }

                if (!child->getTag()) {
                    continue;
                }

                // We found a EQ child of an AND which is tagged.
                RelevantTag* rt = static_cast<RelevantTag*>(child->getTag());

                // Look through all of the indices for which this predicate can be answered with
                // the leading field of the index.
                for (std::vector<size_t>::const_iterator i = rt->first.begin();
                        i != rt->first.end(); ++i) {
                    size_t index = *i;

                    if (indices[index].unique && 1 == indices[index].keyPattern.nFields()) {
                        // Found an EQ predicate which can use a single-field unique index.
                        // Clear assignments from the entire tree, and add back a single assignment
                        // for 'child' to the unique index.
                        clearAssignments(node);
                        RelevantTag* newRt = static_cast<RelevantTag*>(child->getTag());
                        newRt->first.push_back(index);

                        // Tag state has been reset in the entire subtree at 'root'; nothing
                        // else for us to do.
                        return;
                    }
                }
            }
        }

        for (size_t i = 0; i < node->numChildren(); i++) {
            stripUnneededAssignments(node->getChild(i), indices);
        }
    }

    //
    // Helpers used by stripInvalidAssignments
    //

    /**
     * Remove 'idx' from the RelevantTag lists for 'node'.  'node' must be a leaf.
     */
    static void removeIndexRelevantTag(MatchExpression* node, size_t idx) {
        RelevantTag* tag = static_cast<RelevantTag*>(node->getTag());
        verify(tag);
        vector<size_t>::iterator firstIt = std::find(tag->first.begin(),
                                                     tag->first.end(),
                                                     idx);
        if (firstIt != tag->first.end()) {
            tag->first.erase(firstIt);
        }

        vector<size_t>::iterator notFirstIt = std::find(tag->notFirst.begin(),
                                                        tag->notFirst.end(),
                                                        idx);
        if (notFirstIt != tag->notFirst.end()) {
            tag->notFirst.erase(notFirstIt);
        }
    }

    //
    // Text index quirks
    //

    /**
     * Traverse the subtree rooted at 'node' to remove invalid RelevantTag assignments to text index
     * 'idx', which has prefix paths 'prefixPaths'.
     */
    static void stripInvalidAssignmentsToTextIndex(MatchExpression* node,
                                                   size_t idx,
            const unordered_set<StringData, StringData::Hasher>& prefixPaths) {

        // If we're here, there are prefixPaths and node is either:
        // 1. a text pred which we can't use as we have nothing over its prefix, or
        // 2. a non-text pred which we can't use as we don't have a text pred AND-related.
        if (Indexability::nodeCanUseIndexOnOwnField(node)) {
            removeIndexRelevantTag(node, idx);
            return;
        }

        // Do not traverse tree beyond negation node.
        if (node->matchType() == MatchExpression::NOT
            || node->matchType() == MatchExpression::NOR) {

            return;
        }

        // For anything to use a text index with prefixes, we require that:
        // 1. The text pred exists in an AND,
        // 2. The non-text preds that use the text index's prefixes are also in that AND.

        if (node->matchType() != MatchExpression::AND) {
            // It's an OR or some kind of array operator.
            for (size_t i = 0; i < node->numChildren(); ++i) {
                stripInvalidAssignmentsToTextIndex(node->getChild(i), idx, prefixPaths);
            }
            return;
        }

        // If we're here, we're an AND.  Determine whether the children satisfy the index prefix for
        // the text index.
        invariant(node->matchType() == MatchExpression::AND);

        bool hasText = false;

        // The AND must have an EQ predicate for each prefix path.  When we encounter a child with a
        // tag we remove it from childrenPrefixPaths.  All children exist if this set is empty at
        // the end.
        unordered_set<StringData, StringData::Hasher> childrenPrefixPaths = prefixPaths;

        for (size_t i = 0; i < node->numChildren(); ++i) {
            MatchExpression* child = node->getChild(i);
            RelevantTag* tag = static_cast<RelevantTag*>(child->getTag());

            if (NULL == tag) {
                // 'child' could be a logical operator.  Maybe there are some assignments hiding
                // inside.
                stripInvalidAssignmentsToTextIndex(child, idx, prefixPaths);
                continue;
            }

            bool inFirst = tag->first.end() != std::find(tag->first.begin(),
                                                         tag->first.end(),
                                                         idx);

            bool inNotFirst = tag->notFirst.end() != std::find(tag->notFirst.begin(),
                                                               tag->notFirst.end(),
                                                               idx);

            if (inFirst || inNotFirst) {
                // Great!  'child' was assigned to our index.
                if (child->matchType() == MatchExpression::TEXT) {
                    hasText = true;
                }
                else {
                    childrenPrefixPaths.erase(child->path());
                    // One fewer prefix we're looking for, possibly.  Note that we could have a
                    // suffix assignment on the index and wind up here.  In this case the erase
                    // above won't do anything since a suffix isn't a prefix.
                }
            }
            else {
                // Recurse on the children to ensure that they're not hiding any assignments
                // to idx.
                stripInvalidAssignmentsToTextIndex(child, idx, prefixPaths);
            }
        }

        // Our prereqs for using the text index were not satisfied so we remove the assignments from
        // all children of the AND.
        if (!hasText || !childrenPrefixPaths.empty()) {
            for (size_t i = 0; i < node->numChildren(); ++i) {
                stripInvalidAssignmentsToTextIndex(node->getChild(i), idx, prefixPaths);
            }
        }
    }

    // static
    void QueryPlannerIXSelect::stripInvalidAssignmentsToTextIndexes(
        MatchExpression* node,
        const vector<IndexEntry>& indices) {

        for (size_t i = 0; i < indices.size(); ++i) {
            const IndexEntry& index = indices[i];

            // We only care about text indices.
            if (INDEX_TEXT != index.type) {
                continue;
            }

            // Gather the set of paths that comprise the index prefix for this text index.
            // Each of those paths must have an equality assignment, otherwise we can't assign
            // *anything* to this index.
            unordered_set<StringData, StringData::Hasher> textIndexPrefixPaths;
            BSONObjIterator it(index.keyPattern);

            // We stop when we see the first string in the key pattern.  We know that
            // the prefix precedes "text".
            for (BSONElement elt = it.next(); elt.type() != String; elt = it.next()) {
                textIndexPrefixPaths.insert(elt.fieldName());
                verify(it.more());
            }

            // If the index prefix is non-empty, remove invalid assignments to it.
            if (!textIndexPrefixPaths.empty()) {
                stripInvalidAssignmentsToTextIndex(node, i, textIndexPrefixPaths);
            }
        }
    }

    //
    // 2dsphere V2 sparse quirks
    //

    static void stripInvalidAssignmentsTo2dsphereIndex(MatchExpression* node, size_t idx) {

        if (Indexability::nodeCanUseIndexOnOwnField(node)
            && MatchExpression::GEO != node->matchType()
            && MatchExpression::GEO_NEAR != node->matchType()) {
            // We found a non-geo predicate tagged to use a V2 2dsphere index which is not
            // and-related to a geo predicate that can use the index.
            removeIndexRelevantTag(node, idx);
            return;
        }

        const MatchExpression::MatchType nodeType = node->matchType();

        // Don't bother peeking inside of negations.
        if (MatchExpression::NOT == nodeType || MatchExpression::NOR == nodeType) {
            return;
        }

        if (MatchExpression::AND != nodeType) {
            // It's an OR or some kind of array operator.
            for (size_t i = 0; i < node->numChildren(); ++i) {
                stripInvalidAssignmentsTo2dsphereIndex(node->getChild(i), idx);
            }
            return;
        }

        bool hasGeoField = false;

        for (size_t i = 0; i < node->numChildren(); ++i) {
            MatchExpression* child = node->getChild(i);
            RelevantTag* tag = static_cast<RelevantTag*>(child->getTag());

            if (NULL == tag) {
                // 'child' could be a logical operator.  Maybe there are some assignments hiding
                // inside.
                stripInvalidAssignmentsTo2dsphereIndex(child, idx);
                continue;
            }

            bool inFirst = tag->first.end() != std::find(tag->first.begin(),
                                                         tag->first.end(),
                                                         idx);

            bool inNotFirst = tag->notFirst.end() != std::find(tag->notFirst.begin(),
                                                               tag->notFirst.end(),
                                                               idx);

            // If there is an index assignment...
            if (inFirst || inNotFirst) {
                // And it's a geo predicate...
                if (MatchExpression::GEO == child->matchType() ||
                    MatchExpression::GEO_NEAR == child->matchType()) {

                    hasGeoField = true;
                }
            }
            else {
                // Recurse on the children to ensure that they're not hiding any assignments
                // to idx.
                stripInvalidAssignmentsTo2dsphereIndex(child, idx);
            }
        }

        // If there isn't a geo predicate our results aren't a subset of what's in the geo index, so
        // if we use the index we'll miss results.
        if (!hasGeoField) {
            for (size_t i = 0; i < node->numChildren(); ++i) {
                stripInvalidAssignmentsTo2dsphereIndex(node->getChild(i), idx);
            }
        }
    }

    // static
    void QueryPlannerIXSelect::stripInvalidAssignmentsTo2dsphereIndices(
        MatchExpression* node,
        const vector<IndexEntry>& indices) {

        for (size_t i = 0; i < indices.size(); ++i) {
            const IndexEntry& index = indices[i];

            // We only worry about 2dsphere indices.
            if (INDEX_2DSPHERE != index.type) {
                continue;
            }

            // They also have to be V2.  Both ignore the sparse flag but V1 is
            // never-sparse, V2 geo-sparse.
            BSONElement elt = index.infoObj["2dsphereIndexVersion"];
            if (elt.eoo()) {
                continue;
            }
            if (!elt.isNumber()) {
                continue;
            }
            if (2 != elt.numberInt()) {
                continue;
            }

            // If every field is geo don't bother doing anything.
            bool allFieldsGeo = true;
            BSONObjIterator it(index.keyPattern);
            while (it.more()) {
                BSONElement elt = it.next();
                if (String != elt.type()) {
                    allFieldsGeo = false;
                    break;
                }
            }
            if (allFieldsGeo) {
                continue;
            }

            // Remove bad assignments from this index.
            stripInvalidAssignmentsTo2dsphereIndex(node, i);
        }
    }

}  // namespace mongo