SERVER-38091 IndexCatalog iterators and accessors should return const entries

43 files changed, 210 insertions, 186 deletions

diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index a874c594874..6a782ac4df7 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -147,7 +147,7 @@ StatusWith<CollModRequest> parseCollModRequest(OperationContext* opCtx,
                                                 << nss.ns());
                 }
             } else {
-                std::vector<IndexDescriptor*> indexes;
+                std::vector<const IndexDescriptor*> indexes;
                 coll->getIndexCatalog()->findIndexesByKeyPattern(
                     opCtx, keyPattern, false, &indexes);
 
diff --git a/src/mongo/db/catalog/collection_compact.cpp b/src/mongo/db/catalog/collection_compact.cpp
index a7d13797fea..6170ac334d1 100644
--- a/src/mongo/db/catalog/collection_compact.cpp
+++ b/src/mongo/db/catalog/collection_compact.cpp
@@ -66,20 +66,9 @@ StatusWith<CompactStats> compactCollection(OperationContext* opCtx,
             return StatusWith<CompactStats>(status);
 
         // Compact all indexes (not including unfinished indexes)
-        std::unique_ptr<IndexCatalog::IndexIterator> ii(
-            indexCatalog->getIndexIterator(opCtx, false));
-        while (ii->more()) {
-            IndexCatalogEntry* entry = ii->next();
-            IndexDescriptor* descriptor = entry->descriptor();
-            IndexAccessMethod* iam = entry->accessMethod();
-
-            LOG(1) << "compacting index: " << descriptor->toString();
-            Status status = iam->compact(opCtx);
-            if (!status.isOK()) {
-                error() << "failed to compact index: " << descriptor->toString();
-                return status;
-            }
-        }
+        status = indexCatalog->compactIndexes(opCtx);
+        if (!status.isOK())
+            return StatusWith<CompactStats>(status);
 
         return StatusWith<CompactStats>(stats);
     }
@@ -93,7 +82,7 @@ StatusWith<CompactStats> compactCollection(OperationContext* opCtx,
         std::unique_ptr<IndexCatalog::IndexIterator> ii(
             indexCatalog->getIndexIterator(opCtx, false));
         while (ii->more()) {
-            IndexDescriptor* descriptor = ii->next()->descriptor();
+            const IndexDescriptor* descriptor = ii->next()->descriptor();
 
             // Compact always creates the new index in the foreground.
             const BSONObj spec =
diff --git a/src/mongo/db/catalog/collection_impl.cpp b/src/mongo/db/catalog/collection_impl.cpp
index 377fb669bd0..79503488959 100644
--- a/src/mongo/db/catalog/collection_impl.cpp
+++ b/src/mongo/db/catalog/collection_impl.cpp
@@ -757,9 +757,9 @@ uint64_t CollectionImpl::getIndexSize(OperationContext* opCtx, BSONObjBuilder* d
     uint64_t totalSize = 0;
 
     while (ii->more()) {
-        IndexCatalogEntry* entry = ii->next();
-        IndexDescriptor* descriptor = entry->descriptor();
-        IndexAccessMethod* iam = entry->accessMethod();
+        const IndexCatalogEntry* entry = ii->next();
+        const IndexDescriptor* descriptor = entry->descriptor();
+        const IndexAccessMethod* iam = entry->accessMethod();
 
         long long ds = iam->getSpaceUsedBytes(opCtx);
 
@@ -996,9 +996,9 @@ void _validateIndexes(OperationContext* opCtx,
     // Validate Indexes.
     while (it->more()) {
         opCtx->checkForInterrupt();
-        IndexCatalogEntry* entry = it->next();
-        IndexDescriptor* descriptor = entry->descriptor();
-        IndexAccessMethod* iam = entry->accessMethod();
+        const IndexCatalogEntry* entry = it->next();
+        const IndexDescriptor* descriptor = entry->descriptor();
+        const IndexAccessMethod* iam = entry->accessMethod();
 
         log(LogComponent::kIndex) << "validating index " << descriptor->indexNamespace() << endl;
         ValidateResults& curIndexResults = (*indexNsResultsMap)[descriptor->indexNamespace()];
@@ -1060,7 +1060,7 @@ void _validateIndexKeyCount(OperationContext* opCtx,
     std::unique_ptr<IndexCatalog::IndexIterator> indexIterator =
         indexCatalog->getIndexIterator(opCtx, false);
     while (indexIterator->more()) {
-        IndexDescriptor* descriptor = indexIterator->next()->descriptor();
+        const IndexDescriptor* descriptor = indexIterator->next()->descriptor();
         ValidateResults& curIndexResults = (*indexNsResultsMap)[descriptor->indexNamespace()];
 
         if (curIndexResults.valid) {
@@ -1253,8 +1253,8 @@ Status CollectionImpl::touch(OperationContext* opCtx,
         std::unique_ptr<IndexCatalog::IndexIterator> ii =
             _indexCatalog->getIndexIterator(opCtx, false);
         while (ii->more()) {
-            IndexCatalogEntry* entry = ii->next();
-            IndexAccessMethod* iam = entry->accessMethod();
+            const IndexCatalogEntry* entry = ii->next();
+            const IndexAccessMethod* iam = entry->accessMethod();
             Status status = iam->touch(opCtx);
             if (!status.isOK())
                 return status;
diff --git a/src/mongo/db/catalog/collection_info_cache_impl.cpp b/src/mongo/db/catalog/collection_info_cache_impl.cpp
index ecbca8a8509..0065fd0ad01 100644
--- a/src/mongo/db/catalog/collection_info_cache_impl.cpp
+++ b/src/mongo/db/catalog/collection_info_cache_impl.cpp
@@ -84,13 +84,14 @@ void CollectionInfoCacheImpl::computeIndexKeys(OperationContext* opCtx) {
     std::unique_ptr<IndexCatalog::IndexIterator> it =
         _collection->getIndexCatalog()->getIndexIterator(opCtx, true);
     while (it->more()) {
-        IndexCatalogEntry* entry = it->next();
-        IndexDescriptor* descriptor = entry->descriptor();
-        IndexAccessMethod* iam = entry->accessMethod();
+        const IndexCatalogEntry* entry = it->next();
+        const IndexDescriptor* descriptor = entry->descriptor();
+        const IndexAccessMethod* iam = entry->accessMethod();
 
         if (descriptor->getAccessMethodName() == IndexNames::WILDCARD) {
             // Obtain the projection used by the $** index's key generator.
-            const auto* pathProj = static_cast<WildcardAccessMethod*>(iam)->getProjectionExec();
+            const auto* pathProj =
+                static_cast<const WildcardAccessMethod*>(iam)->getProjectionExec();
             // If the projection is an exclusion, then we must check the new document's keys on all
             // updates, since we do not exhaustively know the set of paths to be indexed.
             if (pathProj->getType() == ProjectionExecAgg::ProjectionType::kExclusionProjection) {
diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index 70e14b77e18..1eaa1b2934c 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -572,7 +572,7 @@ Status DatabaseImpl::dropCollectionEvenIfSystem(OperationContext* opCtx,
         // rename. In the case that this collection drop gets rolled back, this will incur a
         // performance hit, since those indexes will have to be rebuilt from scratch, but data
         // integrity is maintained.
-        std::vector<IndexDescriptor*> indexesToDrop;
+        std::vector<const IndexDescriptor*> indexesToDrop;
         auto indexIter = collection->getIndexCatalog()->getIndexIterator(opCtx, true);
 
         // Determine which index names are too long. Since we don't have the collection drop optime
diff --git a/src/mongo/db/catalog/drop_indexes.cpp b/src/mongo/db/catalog/drop_indexes.cpp
index 2c25819720b..34f3875155c 100644
--- a/src/mongo/db/catalog/drop_indexes.cpp
+++ b/src/mongo/db/catalog/drop_indexes.cpp
@@ -116,7 +116,7 @@ Status wrappedRun(OperationContext* opCtx,
     }
 
     if (indexElem.type() == Object) {
-        std::vector<IndexDescriptor*> indexes;
+        std::vector<const IndexDescriptor*> indexes;
         collection->getIndexCatalog()->findIndexesByKeyPattern(
             opCtx, indexElem.embeddedObject(), false, &indexes);
         if (indexes.empty()) {
@@ -134,7 +134,7 @@ Status wrappedRun(OperationContext* opCtx,
                                         << indexes[1]->infoObj());
         }
 
-        IndexDescriptor* desc = indexes[0];
+        const IndexDescriptor* desc = indexes[0];
         if (desc->isIdIndex()) {
             return Status(ErrorCodes::InvalidOptions, "cannot drop _id index");
         }
diff --git a/src/mongo/db/catalog/index_catalog.cpp b/src/mongo/db/catalog/index_catalog.cpp
index 7f68b7ef77c..5dc19d473a2 100644
--- a/src/mongo/db/catalog/index_catalog.cpp
+++ b/src/mongo/db/catalog/index_catalog.cpp
@@ -49,7 +49,7 @@ bool IndexIterator::more() {
     return _next != nullptr;
 }
 
-IndexCatalogEntry* IndexIterator::next() {
+const IndexCatalogEntry* IndexIterator::next() {
     if (!more())
         return nullptr;
     _prev = _next;
@@ -62,7 +62,7 @@ ReadyIndexesIterator::ReadyIndexesIterator(OperationContext* const opCtx,
                                            IndexCatalogEntryContainer::const_iterator endIterator)
     : _opCtx(opCtx), _iterator(beginIterator), _endIterator(endIterator) {}
 
-IndexCatalogEntry* ReadyIndexesIterator::_advance() {
+const IndexCatalogEntry* ReadyIndexesIterator::_advance() {
     while (_iterator != _endIterator) {
         IndexCatalogEntry* entry = _iterator->get();
         ++_iterator;
@@ -90,7 +90,7 @@ AllIndexesIterator::AllIndexesIterator(
     _endIterator = _ownedContainer->end();
 }
 
-IndexCatalogEntry* AllIndexesIterator::_advance() {
+const IndexCatalogEntry* AllIndexesIterator::_advance() {
     if (_iterator == _endIterator) {
         return nullptr;
     }
diff --git a/src/mongo/db/catalog/index_catalog.h b/src/mongo/db/catalog/index_catalog.h
index 9d5faf431b8..32fe911962c 100644
--- a/src/mongo/db/catalog/index_catalog.h
+++ b/src/mongo/db/catalog/index_catalog.h
@@ -47,7 +47,6 @@ class Client;
 class Collection;
 
 class IndexDescriptor;
-class IndexAccessMethod;
 struct InsertDeleteOptions;
 
 struct BsonRecord {
@@ -80,19 +79,19 @@ public:
     public:
         virtual ~IndexIterator() = default;
         bool more();
-        IndexCatalogEntry* next();
+        const IndexCatalogEntry* next();
 
     protected:
         /**
          * Advance the underlying iterator and returns the next index entry. Returns nullptr when
          * the iterator is exhausted.
          */
-        virtual IndexCatalogEntry* _advance() = 0;
+        virtual const IndexCatalogEntry* _advance() = 0;
 
     private:
         bool _start = true;
-        IndexCatalogEntry* _prev = nullptr;
-        IndexCatalogEntry* _next = nullptr;
+        const IndexCatalogEntry* _prev = nullptr;
+        const IndexCatalogEntry* _next = nullptr;
     };
 
     class ReadyIndexesIterator : public IndexIterator {
@@ -102,7 +101,7 @@ public:
                              IndexCatalogEntryContainer::const_iterator endIterator);
 
     private:
-        IndexCatalogEntry* _advance() override;
+        const IndexCatalogEntry* _advance() override;
 
         OperationContext* const _opCtx;
         IndexCatalogEntryContainer::const_iterator _iterator;
@@ -120,7 +119,7 @@ public:
                            std::unique_ptr<std::vector<IndexCatalogEntry*>> ownedContainer);
 
     private:
-        IndexCatalogEntry* _advance() override;
+        const IndexCatalogEntry* _advance() override;
 
         OperationContext* const _opCtx;
         std::vector<IndexCatalogEntry*>::const_iterator _iterator;
@@ -205,16 +204,17 @@ public:
      */
     virtual BSONObj getDefaultIdIndexSpec() const = 0;
 
-    virtual IndexDescriptor* findIdIndex(OperationContext* const opCtx) const = 0;
+    virtual const IndexDescriptor* findIdIndex(OperationContext* const opCtx) const = 0;
 
     /**
      * Find index by name.  The index name uniquely identifies an index.
      *
      * @return null if cannot find
      */
-    virtual IndexDescriptor* findIndexByName(OperationContext* const opCtx,
-                                             const StringData name,
-                                             const bool includeUnfinishedIndexes = false) const = 0;
+    virtual const IndexDescriptor* findIndexByName(
+        OperationContext* const opCtx,
+        const StringData name,
+        const bool includeUnfinishedIndexes = false) const = 0;
 
     /**
      * Find index by matching key pattern and collation spec.  The key pattern and collation spec
@@ -226,7 +226,7 @@ public:
      * @return null if cannot find index, otherwise the index with a matching key pattern and
      * collation.
      */
-    virtual IndexDescriptor* findIndexByKeyPatternAndCollationSpec(
+    virtual const IndexDescriptor* findIndexByKeyPatternAndCollationSpec(
         OperationContext* const opCtx,
         const BSONObj& key,
         const BSONObj& collationSpec,
@@ -238,10 +238,11 @@ public:
      *
      * Consider using 'findIndexByName' if expecting to match one index.
      */
-    virtual void findIndexesByKeyPattern(OperationContext* const opCtx,
-                                         const BSONObj& key,
-                                         const bool includeUnfinishedIndexes,
-                                         std::vector<IndexDescriptor*>* const matches) const = 0;
+    virtual void findIndexesByKeyPattern(
+        OperationContext* const opCtx,
+        const BSONObj& key,
+        const bool includeUnfinishedIndexes,
+        std::vector<const IndexDescriptor*>* const matches) const = 0;
 
     /**
      * Returns an index suitable for shard key range scans.
@@ -256,13 +257,13 @@ public:
      *
      * If no such index exists, returns NULL.
      */
-    virtual IndexDescriptor* findShardKeyPrefixedIndex(OperationContext* const opCtx,
-                                                       const BSONObj& shardKey,
-                                                       const bool requireSingleKey) const = 0;
+    virtual const IndexDescriptor* findShardKeyPrefixedIndex(OperationContext* const opCtx,
+                                                             const BSONObj& shardKey,
+                                                             const bool requireSingleKey) const = 0;
 
     virtual void findIndexByType(OperationContext* const opCtx,
                                  const std::string& type,
-                                 std::vector<IndexDescriptor*>& matches,
+                                 std::vector<const IndexDescriptor*>& matches,
                                  const bool includeUnfinishedIndexes = false) const = 0;
 
     /**
@@ -298,10 +299,6 @@ public:
     virtual std::vector<std::shared_ptr<const IndexCatalogEntry>> getAllReadyEntriesShared()
         const = 0;
 
-    virtual IndexAccessMethod* getIndex(const IndexDescriptor* const desc) = 0;
-
-    virtual const IndexAccessMethod* getIndex(const IndexDescriptor* const desc) const = 0;
-
     /**
      * Returns a not-ok Status if there are any unfinished index builds. No new indexes should
      * be built when in this state.
@@ -344,7 +341,7 @@ public:
                                 stdx::function<void(const IndexDescriptor*)> onDropFn) = 0;
     virtual void dropAllIndexes(OperationContext* opCtx, bool includingIdIndex) = 0;
 
-    virtual Status dropIndex(OperationContext* const opCtx, IndexDescriptor* const desc) = 0;
+    virtual Status dropIndex(OperationContext* const opCtx, const IndexDescriptor* const desc) = 0;
 
     /**
      * Drops all incomplete indexes and returns specs. After this, the indexes can be rebuilt.
@@ -370,6 +367,15 @@ public:
     virtual MultikeyPaths getMultikeyPaths(OperationContext* const opCtx,
                                            const IndexDescriptor* const idx) = 0;
 
+    /**
+     * Sets the index 'desc' to be multikey with the provided 'multikeyPaths'.
+     *
+     * See IndexCatalogEntry::setMultikey().
+     */
+    virtual void setMultikeyPaths(OperationContext* const opCtx,
+                                  const IndexDescriptor* const desc,
+                                  const MultikeyPaths& multikeyPaths) = 0;
+
     // ----- data modifiers ------
 
     /**
@@ -405,6 +411,12 @@ public:
                                const bool noWarn,
                                int64_t* const keysDeletedOut) = 0;
 
+    /*
+     * Attempt compaction on all ready indexes to regain disk space, if the storage engine's index
+     * supports compaction in-place.
+     */
+    virtual Status compactIndexes(OperationContext* opCtx) = 0;
+
     virtual std::string getAccessMethodName(const BSONObj& keyPattern) = 0;
 
     /**
diff --git a/src/mongo/db/catalog/index_catalog_impl.cpp b/src/mongo/db/catalog/index_catalog_impl.cpp
index 2d656ba43df..610d199137d 100644
--- a/src/mongo/db/catalog/index_catalog_impl.cpp
+++ b/src/mongo/db/catalog/index_catalog_impl.cpp
@@ -701,7 +701,7 @@ Status IndexCatalogImpl::_doesSpecConflictWithExisting(OperationContext* opCtx,
     // Collections should only have one text index.
     string pluginName = IndexNames::findPluginName(key);
     if (pluginName == IndexNames::TEXT) {
-        vector<IndexDescriptor*> textIndexes;
+        vector<const IndexDescriptor*> textIndexes;
         const bool includeUnfinishedIndexes = true;
         findIndexByType(opCtx, IndexNames::TEXT, textIndexes, includeUnfinishedIndexes);
         if (textIndexes.size() > 0) {
@@ -758,7 +758,7 @@ void IndexCatalogImpl::dropAllIndexes(OperationContext* opCtx,
         std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, true);
         while (ii->more()) {
             seen++;
-            IndexDescriptor* desc = ii->next()->descriptor();
+            const IndexDescriptor* desc = ii->next()->descriptor();
             if (desc->isIdIndex() && includingIdIndex == false) {
                 haveIdIndex = true;
                 continue;
@@ -770,7 +770,7 @@ void IndexCatalogImpl::dropAllIndexes(OperationContext* opCtx,
 
     for (size_t i = 0; i < indexNamesToDrop.size(); i++) {
         string indexName = indexNamesToDrop[i];
-        IndexDescriptor* desc = findIndexByName(opCtx, indexName, true);
+        const IndexDescriptor* desc = findIndexByName(opCtx, indexName, true);
         invariant(desc);
         LOG(1) << "\t dropAllIndexes dropping: " << desc->toString();
         IndexCatalogEntry* entry = _readyIndexes.find(desc);
@@ -813,7 +813,7 @@ void IndexCatalogImpl::dropAllIndexes(OperationContext* opCtx, bool includingIdI
     dropAllIndexes(opCtx, includingIdIndex, {});
 }
 
-Status IndexCatalogImpl::dropIndex(OperationContext* opCtx, IndexDescriptor* desc) {
+Status IndexCatalogImpl::dropIndex(OperationContext* opCtx, const IndexDescriptor* desc) {
     invariant(opCtx->lockState()->isCollectionLockedForMode(_collection->ns().toString(), MODE_X));
     BackgroundOperation::assertNoBgOpInProgForNs(_collection->ns().ns());
     invariant(_buildingIndexes.size() == 0);
@@ -951,6 +951,17 @@ MultikeyPaths IndexCatalogImpl::getMultikeyPaths(OperationContext* opCtx,
     return entry->getMultikeyPaths(opCtx);
 }
 
+void IndexCatalogImpl::setMultikeyPaths(OperationContext* const opCtx,
+                                        const IndexDescriptor* desc,
+                                        const MultikeyPaths& multikeyPaths) {
+    IndexCatalogEntry* entry = _readyIndexes.find(desc);
+    if (!entry) {
+        entry = _buildingIndexes.find(desc);
+    }
+    invariant(entry);
+    entry->setMultikey(opCtx, multikeyPaths);
+};
+
 // ---------------------------
 
 bool IndexCatalogImpl::haveAnyIndexes() const {
@@ -964,7 +975,7 @@ int IndexCatalogImpl::numIndexesTotal(OperationContext* opCtx) const {
 }
 
 int IndexCatalogImpl::numIndexesReady(OperationContext* opCtx) const {
-    std::vector<IndexDescriptor*> itIndexes;
+    std::vector<const IndexDescriptor*> itIndexes;
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, /*includeUnfinished*/ false);
     while (ii->more()) {
         itIndexes.push_back(ii->next()->descriptor());
@@ -977,7 +988,7 @@ int IndexCatalogImpl::numIndexesReady(OperationContext* opCtx) const {
         // entry and the index catalog differ. Log as much information as possible here.
         if (itIndexes.size() != completedIndexes.size()) {
             log() << "index catalog reports: ";
-            for (IndexDescriptor* i : itIndexes) {
+            for (const IndexDescriptor* i : itIndexes) {
                 log() << "  index: " << i->toString();
             }
 
@@ -998,36 +1009,36 @@ bool IndexCatalogImpl::haveIdIndex(OperationContext* opCtx) const {
     return findIdIndex(opCtx) != nullptr;
 }
 
-IndexDescriptor* IndexCatalogImpl::findIdIndex(OperationContext* opCtx) const {
+const IndexDescriptor* IndexCatalogImpl::findIdIndex(OperationContext* opCtx) const {
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, false);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         if (desc->isIdIndex())
             return desc;
     }
     return nullptr;
 }
 
-IndexDescriptor* IndexCatalogImpl::findIndexByName(OperationContext* opCtx,
-                                                   StringData name,
-                                                   bool includeUnfinishedIndexes) const {
+const IndexDescriptor* IndexCatalogImpl::findIndexByName(OperationContext* opCtx,
+                                                         StringData name,
+                                                         bool includeUnfinishedIndexes) const {
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, includeUnfinishedIndexes);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         if (desc->indexName() == name)
             return desc;
     }
     return nullptr;
 }
 
-IndexDescriptor* IndexCatalogImpl::findIndexByKeyPatternAndCollationSpec(
+const IndexDescriptor* IndexCatalogImpl::findIndexByKeyPatternAndCollationSpec(
     OperationContext* opCtx,
     const BSONObj& key,
     const BSONObj& collationSpec,
     bool includeUnfinishedIndexes) const {
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, includeUnfinishedIndexes);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         if (SimpleBSONObjComparator::kInstance.evaluate(desc->keyPattern() == key) &&
             SimpleBSONObjComparator::kInstance.evaluate(
                 desc->infoObj().getObjectField("collation") == collationSpec)) {
@@ -1040,25 +1051,25 @@ IndexDescriptor* IndexCatalogImpl::findIndexByKeyPatternAndCollationSpec(
 void IndexCatalogImpl::findIndexesByKeyPattern(OperationContext* opCtx,
                                                const BSONObj& key,
                                                bool includeUnfinishedIndexes,
-                                               std::vector<IndexDescriptor*>* matches) const {
+                                               std::vector<const IndexDescriptor*>* matches) const {
     invariant(matches);
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, includeUnfinishedIndexes);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         if (SimpleBSONObjComparator::kInstance.evaluate(desc->keyPattern() == key)) {
             matches->push_back(desc);
         }
     }
 }
 
-IndexDescriptor* IndexCatalogImpl::findShardKeyPrefixedIndex(OperationContext* opCtx,
-                                                             const BSONObj& shardKey,
-                                                             bool requireSingleKey) const {
-    IndexDescriptor* best = nullptr;
+const IndexDescriptor* IndexCatalogImpl::findShardKeyPrefixedIndex(OperationContext* opCtx,
+                                                                   const BSONObj& shardKey,
+                                                                   bool requireSingleKey) const {
+    const IndexDescriptor* best = nullptr;
 
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, false);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         bool hasSimpleCollation = desc->infoObj().getObjectField("collation").isEmpty();
 
         if (desc->isPartial())
@@ -1079,31 +1090,17 @@ IndexDescriptor* IndexCatalogImpl::findShardKeyPrefixedIndex(OperationContext* o
 
 void IndexCatalogImpl::findIndexByType(OperationContext* opCtx,
                                        const string& type,
-                                       vector<IndexDescriptor*>& matches,
+                                       vector<const IndexDescriptor*>& matches,
                                        bool includeUnfinishedIndexes) const {
     std::unique_ptr<IndexIterator> ii = getIndexIterator(opCtx, includeUnfinishedIndexes);
     while (ii->more()) {
-        IndexDescriptor* desc = ii->next()->descriptor();
+        const IndexDescriptor* desc = ii->next()->descriptor();
         if (IndexNames::findPluginName(desc->keyPattern()) == type) {
             matches.push_back(desc);
         }
     }
 }
 
-IndexAccessMethod* IndexCatalogImpl::getIndex(const IndexDescriptor* desc) {
-    IndexCatalogEntry* entry = _readyIndexes.find(desc);
-    if (!entry) {
-        entry = _buildingIndexes.find(desc);
-    }
-
-    massert(17334, "cannot find index entry", entry);
-    return entry->accessMethod();
-}
-
-const IndexAccessMethod* IndexCatalogImpl::getIndex(const IndexDescriptor* desc) const {
-    return getEntry(desc)->accessMethod();
-}
-
 const IndexCatalogEntry* IndexCatalogImpl::getEntry(const IndexDescriptor* desc) const {
     const IndexCatalogEntry* entry = _readyIndexes.find(desc);
     if (!entry) {
@@ -1382,6 +1379,22 @@ void IndexCatalogImpl::unindexRecord(OperationContext* opCtx,
     }
 }
 
+Status IndexCatalogImpl::compactIndexes(OperationContext* opCtx) {
+    for (IndexCatalogEntryContainer::const_iterator it = _readyIndexes.begin();
+         it != _readyIndexes.end();
+         ++it) {
+        IndexCatalogEntry* entry = it->get();
+
+        LOG(1) << "compacting index: " << entry->descriptor()->toString();
+        Status status = entry->accessMethod()->compact(opCtx);
+        if (!status.isOK()) {
+            error() << "failed to compact index: " << entry->descriptor()->toString();
+            return status;
+        }
+    }
+    return Status::OK();
+}
+
 std::unique_ptr<IndexCatalog::IndexBuildBlockInterface> IndexCatalogImpl::createIndexBuildBlock(
     OperationContext* opCtx, const BSONObj& spec) {
     return std::make_unique<IndexBuildBlock>(opCtx, _collection, this, spec);
diff --git a/src/mongo/db/catalog/index_catalog_impl.h b/src/mongo/db/catalog/index_catalog_impl.h
index 5bd37d309f8..b07097957d2 100644
--- a/src/mongo/db/catalog/index_catalog_impl.h
+++ b/src/mongo/db/catalog/index_catalog_impl.h
@@ -49,7 +49,6 @@ class Client;
 class Collection;
 
 class IndexDescriptor;
-class IndexAccessMethod;
 struct InsertDeleteOptions;
 
 /**
@@ -87,16 +86,16 @@ public:
      */
     BSONObj getDefaultIdIndexSpec() const override;
 
-    IndexDescriptor* findIdIndex(OperationContext* opCtx) const override;
+    const IndexDescriptor* findIdIndex(OperationContext* opCtx) const override;
 
     /**
      * Find index by name.  The index name uniquely identifies an index.
      *
      * @return null if cannot find
      */
-    IndexDescriptor* findIndexByName(OperationContext* opCtx,
-                                     StringData name,
-                                     bool includeUnfinishedIndexes = false) const override;
+    const IndexDescriptor* findIndexByName(OperationContext* opCtx,
+                                           StringData name,
+                                           bool includeUnfinishedIndexes = false) const override;
 
     /**
      * Find index by matching key pattern and collation spec.  The key pattern and collation spec
@@ -108,7 +107,7 @@ public:
      * @return null if cannot find index, otherwise the index with a matching key pattern and
      * collation.
      */
-    IndexDescriptor* findIndexByKeyPatternAndCollationSpec(
+    const IndexDescriptor* findIndexByKeyPatternAndCollationSpec(
         OperationContext* opCtx,
         const BSONObj& key,
         const BSONObj& collationSpec,
@@ -123,7 +122,7 @@ public:
     void findIndexesByKeyPattern(OperationContext* opCtx,
                                  const BSONObj& key,
                                  bool includeUnfinishedIndexes,
-                                 std::vector<IndexDescriptor*>* matches) const override;
+                                 std::vector<const IndexDescriptor*>* matches) const override;
 
     /**
      * Returns an index suitable for shard key range scans.
@@ -138,13 +137,13 @@ public:
      *
      * If no such index exists, returns NULL.
      */
-    IndexDescriptor* findShardKeyPrefixedIndex(OperationContext* opCtx,
-                                               const BSONObj& shardKey,
-                                               bool requireSingleKey) const override;
+    const IndexDescriptor* findShardKeyPrefixedIndex(OperationContext* opCtx,
+                                                     const BSONObj& shardKey,
+                                                     bool requireSingleKey) const override;
 
     void findIndexByType(OperationContext* opCtx,
                          const std::string& type,
-                         std::vector<IndexDescriptor*>& matches,
+                         std::vector<const IndexDescriptor*>& matches,
                          bool includeUnfinishedIndexes = false) const override;
 
 
@@ -168,9 +167,6 @@ public:
 
     std::vector<std::shared_ptr<const IndexCatalogEntry>> getAllReadyEntriesShared() const override;
 
-    IndexAccessMethod* getIndex(const IndexDescriptor* desc) override;
-    const IndexAccessMethod* getIndex(const IndexDescriptor* desc) const override;
-
     /**
      * Returns a not-ok Status if there are any unfinished index builds. No new indexes should
      * be built when in this state.
@@ -208,7 +204,7 @@ public:
                         stdx::function<void(const IndexDescriptor*)> onDropFn) override;
     void dropAllIndexes(OperationContext* opCtx, bool includingIdIndex) override;
 
-    Status dropIndex(OperationContext* opCtx, IndexDescriptor* desc) override;
+    Status dropIndex(OperationContext* opCtx, const IndexDescriptor* desc) override;
 
     /**
      * will drop all incompleted indexes and return specs
@@ -241,6 +237,10 @@ public:
      */
     MultikeyPaths getMultikeyPaths(OperationContext* opCtx, const IndexDescriptor* idx) override;
 
+    void setMultikeyPaths(OperationContext* const opCtx,
+                          const IndexDescriptor* desc,
+                          const MultikeyPaths& multikeyPaths) override;
+
     // --- these probably become private?
 
     class IndexBuildBlock : public IndexCatalog::IndexBuildBlockInterface {
@@ -330,6 +330,8 @@ public:
                        bool noWarn,
                        int64_t* keysDeletedOut) override;
 
+    Status compactIndexes(OperationContext* opCtx) override;
+
     inline std::string getAccessMethodName(const BSONObj& keyPattern) override {
         return _getAccessMethodName(keyPattern);
     }
diff --git a/src/mongo/db/catalog/index_catalog_noop.h b/src/mongo/db/catalog/index_catalog_noop.h
index 38ec89e7fc4..8005b1dc2a2 100644
--- a/src/mongo/db/catalog/index_catalog_noop.h
+++ b/src/mongo/db/catalog/index_catalog_noop.h
@@ -90,10 +90,11 @@ public:
         return nullptr;
     }
 
-    void findIndexesByKeyPattern(OperationContext* const opCtx,
-                                 const BSONObj& key,
-                                 const bool includeUnfinishedIndexes,
-                                 std::vector<IndexDescriptor*>* const matches) const override {}
+    void findIndexesByKeyPattern(
+        OperationContext* const opCtx,
+        const BSONObj& key,
+        const bool includeUnfinishedIndexes,
+        std::vector<const IndexDescriptor*>* const matches) const override {}
 
     IndexDescriptor* findShardKeyPrefixedIndex(OperationContext* const opCtx,
                                                const BSONObj& shardKey,
@@ -103,7 +104,7 @@ public:
 
     void findIndexByType(OperationContext* const opCtx,
                          const std::string& type,
-                         std::vector<IndexDescriptor*>& matches,
+                         std::vector<const IndexDescriptor*>& matches,
                          const bool includeUnfinishedIndexes = false) const override {}
 
     const IndexDescriptor* refreshEntry(OperationContext* const opCtx,
@@ -124,14 +125,6 @@ public:
         return {};
     }
 
-    IndexAccessMethod* getIndex(const IndexDescriptor* const desc) override {
-        return nullptr;
-    }
-
-    const IndexAccessMethod* getIndex(const IndexDescriptor* const desc) const override {
-        return nullptr;
-    }
-
     Status checkUnfinished() const override {
         return Status::OK();
     }
@@ -163,7 +156,7 @@ public:
 
     void dropAllIndexes(OperationContext* opCtx, bool includingIdIndex) override {}
 
-    Status dropIndex(OperationContext* const opCtx, IndexDescriptor* const desc) override {
+    Status dropIndex(OperationContext* const opCtx, const IndexDescriptor* const desc) override {
         return Status::OK();
     }
 
@@ -180,6 +173,10 @@ public:
         return {};
     }
 
+    void setMultikeyPaths(OperationContext* const opCtx,
+                          const IndexDescriptor* const desc,
+                          const MultikeyPaths& multikeyPaths) override {}
+
     Status indexRecords(OperationContext* const opCtx,
                         const std::vector<BsonRecord>& bsonRecords,
                         int64_t* const keysInsertedOut) override {
@@ -201,6 +198,10 @@ public:
                        const bool noWarn,
                        int64_t* const keysDeletedOut) override {}
 
+    virtual Status compactIndexes(OperationContext* opCtx) override {
+        return Status::OK();
+    }
+
     std::string getAccessMethodName(const BSONObj& keyPattern) override {
         return "";
     }
diff --git a/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp b/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
index 826cbbe4ebf..bc7dace1981 100644
--- a/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
+++ b/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
@@ -89,7 +89,7 @@ Status RecordStoreValidateAdaptor::validate(const RecordId& recordId,
         int indexNumber = _indexConsistency->getIndexNumber(indexNs);
         ValidateResults curRecordResults;
 
-        const IndexAccessMethod* iam = _indexCatalog->getIndex(descriptor);
+        const IndexAccessMethod* iam = _indexCatalog->getEntry(descriptor)->accessMethod();
 
         if (descriptor->isPartial()) {
             const IndexCatalogEntry* ice = _indexCatalog->getEntry(descriptor);
@@ -254,7 +254,7 @@ void RecordStoreValidateAdaptor::traverseRecordStore(RecordStore* recordStore,
     output->appendNumber("nrecords", nrecords);
 }
 
-void RecordStoreValidateAdaptor::validateIndexKeyCount(IndexDescriptor* idx,
+void RecordStoreValidateAdaptor::validateIndexKeyCount(const IndexDescriptor* idx,
                                                        int64_t numRecs,
                                                        ValidateResults& results) {
     const std::string indexNs = idx->indexNamespace();
diff --git a/src/mongo/db/catalog/private/record_store_validate_adaptor.h b/src/mongo/db/catalog/private/record_store_validate_adaptor.h
index 767f0f4562b..a62d0d89041 100644
--- a/src/mongo/db/catalog/private/record_store_validate_adaptor.h
+++ b/src/mongo/db/catalog/private/record_store_validate_adaptor.h
@@ -91,7 +91,9 @@ public:
     /**
      * Validate that the number of document keys matches the number of index keys.
      */
-    void validateIndexKeyCount(IndexDescriptor* idx, int64_t numRecs, ValidateResults& results);
+    void validateIndexKeyCount(const IndexDescriptor* idx,
+                               int64_t numRecs,
+                               ValidateResults& results);
 
 private:
     OperationContext* _opCtx;             // Not owned.
diff --git a/src/mongo/db/catalog/rename_collection.cpp b/src/mongo/db/catalog/rename_collection.cpp
index 07326f7b5b0..17511b348b5 100644
--- a/src/mongo/db/catalog/rename_collection.cpp
+++ b/src/mongo/db/catalog/rename_collection.cpp
@@ -299,7 +299,7 @@ Status renameCollectionCommon(OperationContext* opCtx,
                 // drop-pending rename. In the case that this collection drop gets rolled back, this
                 // will incur a performance hit, since those indexes will have to be rebuilt from
                 // scratch, but data integrity is maintained.
-                std::vector<IndexDescriptor*> indexesToDrop;
+                std::vector<const IndexDescriptor*> indexesToDrop;
                 auto indexIter = targetColl->getIndexCatalog()->getIndexIterator(opCtx, true);
 
                 // Determine which index names are too long. Since we don't have the collection
diff --git a/src/mongo/db/commands/dbcommands.cpp b/src/mongo/db/commands/dbcommands.cpp
index 5df659e062c..2190cdc3910 100644
--- a/src/mongo/db/commands/dbcommands.cpp
+++ b/src/mongo/db/commands/dbcommands.cpp
@@ -448,7 +448,7 @@ public:
                 keyPattern = Helpers::inferKeyPattern(min);
             }
 
-            IndexDescriptor* idx =
+            const IndexDescriptor* idx =
                 collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx,
                                                                          keyPattern,
                                                                          true);  // requireSingleKey
diff --git a/src/mongo/db/commands/dbhash.cpp b/src/mongo/db/commands/dbhash.cpp
index e3abe5437b4..5cbcc0015ba 100644
--- a/src/mongo/db/commands/dbhash.cpp
+++ b/src/mongo/db/commands/dbhash.cpp
@@ -246,7 +246,7 @@ private:
             invariant(opCtx->lockState()->isDbLockedForMode(db->name(), MODE_S));
         }
 
-        IndexDescriptor* desc = collection->getIndexCatalog()->findIdIndex(opCtx);
+        auto desc = collection->getIndexCatalog()->findIdIndex(opCtx);
 
         std::unique_ptr<PlanExecutor, PlanExecutor::Deleter> exec;
         if (desc) {
diff --git a/src/mongo/db/commands/haystack.cpp b/src/mongo/db/commands/haystack.cpp
index 123e63d4e1c..56d145a3276 100644
--- a/src/mongo/db/commands/haystack.cpp
+++ b/src/mongo/db/commands/haystack.cpp
@@ -116,7 +116,7 @@ public:
             return false;
         }
 
-        vector<IndexDescriptor*> idxs;
+        vector<const IndexDescriptor*> idxs;
         collection->getIndexCatalog()->findIndexByType(opCtx, IndexNames::GEO_HAYSTACK, idxs);
         if (idxs.size() == 0) {
             errmsg = "no geoSearch index";
@@ -139,9 +139,9 @@ public:
         if (cmdObj["limit"].isNumber())
             limit = static_cast<unsigned>(cmdObj["limit"].numberInt());
 
-        IndexDescriptor* desc = idxs[0];
-        HaystackAccessMethod* ham =
-            static_cast<HaystackAccessMethod*>(collection->getIndexCatalog()->getIndex(desc));
+        const IndexDescriptor* desc = idxs[0];
+        auto ham = static_cast<const HaystackAccessMethod*>(
+            collection->getIndexCatalog()->getEntry(desc)->accessMethod());
         ham->searchCommand(opCtx,
                            collection,
                            nearElt.Obj(),
diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 0c3110cb97b..6d3ad0e9a50 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -536,7 +536,7 @@ void State::prepTempCollection() {
                 finalColl->getIndexCatalog()->getIndexIterator(_opCtx, true);
             // Iterate over finalColl's indexes.
             while (ii->more()) {
-                IndexDescriptor* currIndex = ii->next()->descriptor();
+                const IndexDescriptor* currIndex = ii->next()->descriptor();
                 BSONObjBuilder b;
                 b.append("ns", _config.tempNamespace.ns());
 
@@ -1124,7 +1124,7 @@ void State::finalReduce(OperationContext* opCtx, CurOp* curOp, ProgressMeterHold
             autoIncColl.getCollection()->getIndexCatalog()->getIndexIterator(_opCtx, true);
         // Iterate over incColl's indexes.
         while (ii->more()) {
-            IndexDescriptor* currIndex = ii->next()->descriptor();
+            const IndexDescriptor* currIndex = ii->next()->descriptor();
             BSONObj x = currIndex->infoObj();
             if (sortKey.woCompare(x["key"].embeddedObject()) == 0) {
                 foundIndex = true;
diff --git a/src/mongo/db/dbhelpers.cpp b/src/mongo/db/dbhelpers.cpp
index 4c547d68a7e..d1b5b9518fa 100644
--- a/src/mongo/db/dbhelpers.cpp
+++ b/src/mongo/db/dbhelpers.cpp
@@ -165,7 +165,7 @@ bool Helpers::findById(OperationContext* opCtx,
     if (indexFound)
         *indexFound = 1;
 
-    RecordId loc = catalog->getIndex(desc)->findSingle(opCtx, query["_id"].wrap());
+    RecordId loc = catalog->getEntry(desc)->accessMethod()->findSingle(opCtx, query["_id"].wrap());
     if (loc.isNull())
         return false;
     result = collection->docFor(opCtx, loc).value();
@@ -179,7 +179,7 @@ RecordId Helpers::findById(OperationContext* opCtx,
     IndexCatalog* catalog = collection->getIndexCatalog();
     const IndexDescriptor* desc = catalog->findIdIndex(opCtx);
     uassert(13430, "no _id index", desc);
-    return catalog->getIndex(desc)->findSingle(opCtx, idquery["_id"].wrap());
+    return catalog->getEntry(desc)->accessMethod()->findSingle(opCtx, idquery["_id"].wrap());
 }
 
 bool Helpers::getSingleton(OperationContext* opCtx, const char* ns, BSONObj& result) {
diff --git a/src/mongo/db/exec/stagedebug_cmd.cpp b/src/mongo/db/exec/stagedebug_cmd.cpp
index ebcd2208952..2a9aa368cf3 100644
--- a/src/mongo/db/exec/stagedebug_cmd.cpp
+++ b/src/mongo/db/exec/stagedebug_cmd.cpp
@@ -274,11 +274,11 @@ public:
         string nodeName = firstElt.fieldName();
 
         if ("ixscan" == nodeName) {
-            IndexDescriptor* desc;
+            const IndexDescriptor* desc;
             if (BSONElement keyPatternElement = nodeArgs["keyPattern"]) {
                 // This'll throw if it's not an obj but that's OK.
                 BSONObj keyPatternObj = keyPatternElement.Obj();
-                std::vector<IndexDescriptor*> indexes;
+                std::vector<const IndexDescriptor*> indexes;
                 collection->getIndexCatalog()->findIndexesByKeyPattern(
                     opCtx, keyPatternObj, false, &indexes);
                 uassert(16890,
@@ -453,13 +453,14 @@ public:
         } else if ("text" == nodeName) {
             string search = nodeArgs["search"].String();
 
-            vector<IndexDescriptor*> idxMatches;
+            vector<const IndexDescriptor*> idxMatches;
             collection->getIndexCatalog()->findIndexByType(opCtx, "text", idxMatches);
             uassert(17194, "Expected exactly one text index", idxMatches.size() == 1);
 
-            IndexDescriptor* index = idxMatches[0];
-            FTSAccessMethod* fam =
-                dynamic_cast<FTSAccessMethod*>(collection->getIndexCatalog()->getIndex(index));
+            const IndexDescriptor* index = idxMatches[0];
+            const FTSAccessMethod* fam = dynamic_cast<const FTSAccessMethod*>(
+                collection->getIndexCatalog()->getEntry(index)->accessMethod());
+            invariant(fam);
             TextStageParams params(fam->getSpec());
             params.index = index;
 
diff --git a/src/mongo/db/index/haystack_access_method.cpp b/src/mongo/db/index/haystack_access_method.cpp
index ed57097f0b5..117feda7bc8 100644
--- a/src/mongo/db/index/haystack_access_method.cpp
+++ b/src/mongo/db/index/haystack_access_method.cpp
@@ -78,7 +78,7 @@ void HaystackAccessMethod::searchCommand(OperationContext* opCtx,
                                          double maxDistance,
                                          const BSONObj& search,
                                          BSONObjBuilder* result,
-                                         unsigned limit) {
+                                         unsigned limit) const {
     Timer t;
 
     LOG(1) << "SEARCH near:" << redact(nearObj) << " maxDistance:" << maxDistance
diff --git a/src/mongo/db/index/haystack_access_method.h b/src/mongo/db/index/haystack_access_method.h
index bd328eb007a..547a0057785 100644
--- a/src/mongo/db/index/haystack_access_method.h
+++ b/src/mongo/db/index/haystack_access_method.h
@@ -68,7 +68,7 @@ protected:
                        double maxDistance,
                        const BSONObj& search,
                        BSONObjBuilder* result,
-                       unsigned limit);
+                       unsigned limit) const;
 
 private:
     /**
diff --git a/src/mongo/db/index/index_access_method.cpp b/src/mongo/db/index/index_access_method.cpp
index 47d9846d58b..4092077bbac 100644
--- a/src/mongo/db/index/index_access_method.cpp
+++ b/src/mongo/db/index/index_access_method.cpp
@@ -378,7 +378,7 @@ RecordId AbstractIndexAccessMethod::findSingle(OperationContext* opCtx,
 
 void AbstractIndexAccessMethod::validate(OperationContext* opCtx,
                                          int64_t* numKeys,
-                                         ValidateResults* fullResults) {
+                                         ValidateResults* fullResults) const {
     long long keys = 0;
     _newInterface->fullValidate(opCtx, &keys, fullResults);
     *numKeys = keys;
diff --git a/src/mongo/db/index/index_access_method.h b/src/mongo/db/index/index_access_method.h
index 3c466486410..1edf7fdd209 100644
--- a/src/mongo/db/index/index_access_method.h
+++ b/src/mongo/db/index/index_access_method.h
@@ -188,7 +188,7 @@ public:
      */
     virtual void validate(OperationContext* opCtx,
                           int64_t* numKeys,
-                          ValidateResults* fullResults) = 0;
+                          ValidateResults* fullResults) const = 0;
 
     /**
      * Add custom statistics about this index to BSON object builder, for display.
@@ -500,7 +500,9 @@ public:
 
     Status touch(OperationContext* opCtx) const final;
 
-    void validate(OperationContext* opCtx, int64_t* numKeys, ValidateResults* fullResults) final;
+    void validate(OperationContext* opCtx,
+                  int64_t* numKeys,
+                  ValidateResults* fullResults) const final;
 
     bool appendCustomStats(OperationContext* opCtx,
                            BSONObjBuilder* result,
diff --git a/src/mongo/db/matcher/expression_text.cpp b/src/mongo/db/matcher/expression_text.cpp
index 8f486314e5c..561aedd5465 100644
--- a/src/mongo/db/matcher/expression_text.cpp
+++ b/src/mongo/db/matcher/expression_text.cpp
@@ -77,7 +77,7 @@ TextMatchExpression::TextMatchExpression(OperationContext* opCtx,
                               << "')",
                 collection);
 
-        std::vector<IndexDescriptor*> idxMatches;
+        std::vector<const IndexDescriptor*> idxMatches;
         collection->getIndexCatalog()->findIndexByType(opCtx, IndexNames::TEXT, idxMatches);
 
         uassert(
@@ -87,9 +87,9 @@ TextMatchExpression::TextMatchExpression(OperationContext* opCtx,
                 idxMatches.size() < 2);
         invariant(idxMatches.size() == 1);
 
-        IndexDescriptor* index = idxMatches[0];
-        const FTSAccessMethod* fam =
-            static_cast<FTSAccessMethod*>(collection->getIndexCatalog()->getIndex(index));
+        const IndexDescriptor* index = idxMatches[0];
+        const FTSAccessMethod* fam = static_cast<const FTSAccessMethod*>(
+            collection->getIndexCatalog()->getEntry(index)->accessMethod());
         invariant(fam);
 
         // Extract version and default language from text index.
diff --git a/src/mongo/db/pipeline/pipeline_d.cpp b/src/mongo/db/pipeline/pipeline_d.cpp
index 9aaa69ce2c1..6e706c1e1f2 100644
--- a/src/mongo/db/pipeline/pipeline_d.cpp
+++ b/src/mongo/db/pipeline/pipeline_d.cpp
@@ -255,7 +255,7 @@ BSONObj removeSortKeyMetaProjection(BSONObj projectionObj) {
 StringData extractGeoNearFieldFromIndexes(OperationContext* opCtx, Collection* collection) {
     invariant(collection);
 
-    std::vector<IndexDescriptor*> idxs;
+    std::vector<const IndexDescriptor*> idxs;
     collection->getIndexCatalog()->findIndexByType(opCtx, IndexNames::GEO_2D, idxs);
     uassert(ErrorCodes::IndexNotFound,
             str::stream() << "There is more than one 2d index on " << collection->ns().ns()
diff --git a/src/mongo/db/pipeline/process_interface_standalone.cpp b/src/mongo/db/pipeline/process_interface_standalone.cpp
index bff692e7641..70330f1fe3b 100644
--- a/src/mongo/db/pipeline/process_interface_standalone.cpp
+++ b/src/mongo/db/pipeline/process_interface_standalone.cpp
@@ -505,7 +505,7 @@ bool MongoInterfaceStandalone::uniqueKeyIsSupportedByIndex(
 
     auto indexIterator = collection->getIndexCatalog()->getIndexIterator(opCtx, false);
     while (indexIterator->more()) {
-        IndexCatalogEntry* entry = indexIterator->next();
+        const IndexCatalogEntry* entry = indexIterator->next();
         if (supportsUniqueKey(expCtx, entry, uniqueKeyPaths)) {
             return true;
         }
diff --git a/src/mongo/db/query/get_executor.cpp b/src/mongo/db/query/get_executor.cpp
index 0e24ef31472..b9b1776f426 100644
--- a/src/mongo/db/query/get_executor.cpp
+++ b/src/mongo/db/query/get_executor.cpp
@@ -210,7 +210,7 @@ void fillOutPlannerParams(OperationContext* opCtx,
     std::unique_ptr<IndexCatalog::IndexIterator> ii =
         collection->getIndexCatalog()->getIndexIterator(opCtx, false);
     while (ii->more()) {
-        IndexCatalogEntry* ice = ii->next();
+        const IndexCatalogEntry* ice = ii->next();
         plannerParams->indices.push_back(
             indexEntryFromIndexCatalogEntry(opCtx, *ice, canonicalQuery));
     }
@@ -1516,7 +1516,7 @@ QueryPlannerParams fillOutPlannerParamsForDistinct(OperationContext* opCtx,
         collection->getIndexCatalog()->getIndexIterator(opCtx, false);
     auto query = parsedDistinct.getQuery()->getQueryRequest().getFilter();
     while (ii->more()) {
-        IndexCatalogEntry* ice = ii->next();
+        const IndexCatalogEntry* ice = ii->next();
         const IndexDescriptor* desc = ice->descriptor();
         if (desc->keyPattern().hasField(parsedDistinct.getKey())) {
             plannerParams.indices.push_back(
@@ -1524,7 +1524,7 @@ QueryPlannerParams fillOutPlannerParamsForDistinct(OperationContext* opCtx,
         } else if (desc->getIndexType() == IndexType::INDEX_WILDCARD && !query.isEmpty()) {
             // Check whether the $** projection captures the field over which we are distinct-ing.
             const auto* proj =
-                static_cast<WildcardAccessMethod*>(ice->accessMethod())->getProjectionExec();
+                static_cast<const WildcardAccessMethod*>(ice->accessMethod())->getProjectionExec();
             if (proj->applyProjectionToOneField(parsedDistinct.getKey())) {
                 plannerParams.indices.push_back(
                     indexEntryFromIndexCatalogEntry(opCtx, *ice, parsedDistinct.getQuery()));
diff --git a/src/mongo/db/query/stage_builder.cpp b/src/mongo/db/query/stage_builder.cpp
index c6ff07b9783..511c9c32c26 100644
--- a/src/mongo/db/query/stage_builder.cpp
+++ b/src/mongo/db/query/stage_builder.cpp
@@ -246,7 +246,7 @@ PlanStage* buildStages(OperationContext* opCtx,
             params.addPointMeta = node->addPointMeta;
             params.addDistMeta = node->addDistMeta;
 
-            IndexDescriptor* twoDIndex = collection->getIndexCatalog()->findIndexByName(
+            const IndexDescriptor* twoDIndex = collection->getIndexCatalog()->findIndexByName(
                 opCtx, node->index.identifier.catalogName);
             invariant(twoDIndex);
 
@@ -264,7 +264,7 @@ PlanStage* buildStages(OperationContext* opCtx,
             params.addPointMeta = node->addPointMeta;
             params.addDistMeta = node->addDistMeta;
 
-            IndexDescriptor* s2Index = collection->getIndexCatalog()->findIndexByName(
+            const IndexDescriptor* s2Index = collection->getIndexCatalog()->findIndexByName(
                 opCtx, node->index.identifier.catalogName);
             invariant(s2Index);
 
@@ -272,11 +272,11 @@ PlanStage* buildStages(OperationContext* opCtx,
         }
         case STAGE_TEXT: {
             const TextNode* node = static_cast<const TextNode*>(root);
-            IndexDescriptor* desc = collection->getIndexCatalog()->findIndexByName(
+            const IndexDescriptor* desc = collection->getIndexCatalog()->findIndexByName(
                 opCtx, node->index.identifier.catalogName);
             invariant(desc);
-            const FTSAccessMethod* fam =
-                static_cast<const FTSAccessMethod*>(collection->getIndexCatalog()->getIndex(desc));
+            const FTSAccessMethod* fam = static_cast<const FTSAccessMethod*>(
+                collection->getIndexCatalog()->getEntry(desc)->accessMethod());
             invariant(fam);
 
             TextStageParams params(fam->getSpec());
diff --git a/src/mongo/db/repl/dbcheck.cpp b/src/mongo/db/repl/dbcheck.cpp
index f07748076b0..798a751210a 100644
--- a/src/mongo/db/repl/dbcheck.cpp
+++ b/src/mongo/db/repl/dbcheck.cpp
@@ -190,7 +190,7 @@ DbCheckHasher::DbCheckHasher(OperationContext* opCtx,
     md5_init(&_state);
 
     // Get the _id index.
-    IndexDescriptor* desc = collection->getIndexCatalog()->findIdIndex(opCtx);
+    const IndexDescriptor* desc = collection->getIndexCatalog()->findIdIndex(opCtx);
 
     uassert(ErrorCodes::IndexNotFound, "dbCheck needs _id index", desc);
 
diff --git a/src/mongo/db/repl/idempotency_test_fixture.cpp b/src/mongo/db/repl/idempotency_test_fixture.cpp
index c95da4afa31..48e3d97f5c6 100644
--- a/src/mongo/db/repl/idempotency_test_fixture.cpp
+++ b/src/mongo/db/repl/idempotency_test_fixture.cpp
@@ -403,7 +403,7 @@ OplogEntry IdempotencyTest::dropIndex(const std::string& indexName) {
 }
 
 std::string IdempotencyTest::computeDataHash(Collection* collection) {
-    IndexDescriptor* desc = collection->getIndexCatalog()->findIdIndex(_opCtx.get());
+    auto desc = collection->getIndexCatalog()->findIdIndex(_opCtx.get());
     ASSERT_TRUE(desc);
     auto exec = InternalPlanner::indexScan(_opCtx.get(),
                                            collection,
diff --git a/src/mongo/db/repl/rs_rollback_test.cpp b/src/mongo/db/repl/rs_rollback_test.cpp
index c91e088be2d..51f266dfcf5 100644
--- a/src/mongo/db/repl/rs_rollback_test.cpp
+++ b/src/mongo/db/repl/rs_rollback_test.cpp
@@ -712,7 +712,7 @@ TEST_F(RSRollbackTest, RollingBackCreateIndexAndRenameWithLongName) {
         ASSERT(indexCatalog);
         ASSERT_EQUALS(1, indexCatalog->numIndexesReady(_opCtx.get()));
 
-        std::vector<IndexDescriptor*> indexes;
+        std::vector<const IndexDescriptor*> indexes;
         indexCatalog->findIndexesByKeyPattern(_opCtx.get(), BSON("b" << 1), false, &indexes);
         ASSERT(indexes.size() == 0);
     }
@@ -771,12 +771,12 @@ TEST_F(RSRollbackTest, RollingBackDropAndCreateOfSameIndexNameWithDifferentSpecs
                                               << ", UUID: "
                                               << options.uuid->toString()
                                               << ", index: a_1"));
-        std::vector<IndexDescriptor*> indexes;
+        std::vector<const IndexDescriptor*> indexes;
         indexCatalog->findIndexesByKeyPattern(_opCtx.get(), BSON("a" << 1), false, &indexes);
         ASSERT(indexes.size() == 1);
         ASSERT(indexes[0]->indexName() == "a_1");
 
-        std::vector<IndexDescriptor*> indexes2;
+        std::vector<const IndexDescriptor*> indexes2;
         indexCatalog->findIndexesByKeyPattern(_opCtx.get(), BSON("b" << 1), false, &indexes2);
         ASSERT(indexes2.size() == 0);
     }
diff --git a/src/mongo/db/repl/storage_interface_impl.cpp b/src/mongo/db/repl/storage_interface_impl.cpp
index a6ba88502bc..8d96d926e95 100644
--- a/src/mongo/db/repl/storage_interface_impl.cpp
+++ b/src/mongo/db/repl/storage_interface_impl.cpp
@@ -528,7 +528,7 @@ Status StorageInterfaceImpl::setIndexIsMultikey(OperationContext* opCtx,
                                         << nss.ns()
                                         << " to set to multikey.");
         }
-        collection->getIndexCatalog()->getIndex(idx)->setIndexIsMultikey(opCtx, paths);
+        collection->getIndexCatalog()->setMultikeyPaths(opCtx, idx, paths);
         wunit.commit();
         return Status::OK();
     });
@@ -609,7 +609,7 @@ StatusWith<std::vector<BSONObj>> _findOrDeleteDocuments(
                 auto indexCatalog = collection->getIndexCatalog();
                 invariant(indexCatalog);
                 bool includeUnfinishedIndexes = false;
-                IndexDescriptor* indexDescriptor =
+                const IndexDescriptor* indexDescriptor =
                     indexCatalog->findIndexByName(opCtx, *indexName, includeUnfinishedIndexes);
                 if (!indexDescriptor) {
                     return Result(ErrorCodes::IndexNotFound,
diff --git a/src/mongo/db/repl/storage_interface_impl_test.cpp b/src/mongo/db/repl/storage_interface_impl_test.cpp
index cc5702f542c..dbc679c9a4d 100644
--- a/src/mongo/db/repl/storage_interface_impl_test.cpp
+++ b/src/mongo/db/repl/storage_interface_impl_test.cpp
@@ -162,8 +162,8 @@ TimestampedBSONObj makeOplogEntry(OpTime opTime) {
 /**
  * Counts the number of keys in an index using an IndexAccessMethod::validate call.
  */
-int64_t getIndexKeyCount(OperationContext* opCtx, IndexCatalog* cat, IndexDescriptor* desc) {
-    auto idx = cat->getIndex(desc);
+int64_t getIndexKeyCount(OperationContext* opCtx, IndexCatalog* cat, const IndexDescriptor* desc) {
+    auto idx = cat->getEntry(desc)->accessMethod();
     int64_t numKeys;
     ValidateResults fullRes;
     idx->validate(opCtx, &numKeys, &fullRes);
diff --git a/src/mongo/db/s/check_sharding_index_command.cpp b/src/mongo/db/s/check_sharding_index_command.cpp
index 38e4b44a6d1..cf25be9b60e 100644
--- a/src/mongo/db/s/check_sharding_index_command.cpp
+++ b/src/mongo/db/s/check_sharding_index_command.cpp
@@ -118,7 +118,7 @@ public:
             return false;
         }
 
-        IndexDescriptor* idx =
+        const IndexDescriptor* idx =
             collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx,
                                                                      keyPattern,
                                                                      true);  // requireSingleKey
diff --git a/src/mongo/db/s/collection_range_deleter.cpp b/src/mongo/db/s/collection_range_deleter.cpp
index 8c9bfb4ccd7..8856d53d8a2 100644
--- a/src/mongo/db/s/collection_range_deleter.cpp
+++ b/src/mongo/db/s/collection_range_deleter.cpp
@@ -377,7 +377,8 @@ StatusWith<int> CollectionRangeDeleter::_doDeletion(OperationContext* opCtx,
     LOG(1) << "begin removal of " << min << " to " << max << " in " << nss.ns();
 
     const auto indexName = idx->indexName();
-    IndexDescriptor* descriptor = collection->getIndexCatalog()->findIndexByName(opCtx, indexName);
+    const IndexDescriptor* descriptor =
+        collection->getIndexCatalog()->findIndexByName(opCtx, indexName);
     if (!descriptor) {
         std::string msg = str::stream() << "shard key index with name " << indexName << " on '"
                                         << nss.ns() << "' was dropped";
diff --git a/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp b/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
index 2f1c79c58ad..716083aed25 100644
--- a/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
+++ b/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
@@ -548,7 +548,7 @@ Status MigrationChunkClonerSourceLegacy::_storeCurrentLocs(OperationContext* opC
 
     // Allow multiKey based on the invariant that shard keys must be single-valued. Therefore, any
     // multi-key index prefixed by shard key cannot be multikey over the shard key fields.
-    IndexDescriptor* const idx =
+    const IndexDescriptor* idx =
         collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx,
                                                                  _shardKeyPattern.toBSON(),
                                                                  false);  // requireSingleKey
diff --git a/src/mongo/db/s/split_chunk.cpp b/src/mongo/db/s/split_chunk.cpp
index d3c0a6908db..b1cb6c5a93e 100644
--- a/src/mongo/db/s/split_chunk.cpp
+++ b/src/mongo/db/s/split_chunk.cpp
@@ -230,7 +230,7 @@ StatusWith<boost::optional<ChunkRange>> splitChunk(OperationContext* opCtx,
 
     // Allow multiKey based on the invariant that shard keys must be single-valued. Therefore,
     // any multi-key index prefixed by shard key cannot be multikey over the shard key fields.
-    IndexDescriptor* idx =
+    const IndexDescriptor* idx =
         collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx, keyPatternObj, false);
     if (!idx) {
         return boost::optional<ChunkRange>(boost::none);
diff --git a/src/mongo/db/s/split_vector.cpp b/src/mongo/db/s/split_vector.cpp
index 91d6804176b..8d759163347 100644
--- a/src/mongo/db/s/split_vector.cpp
+++ b/src/mongo/db/s/split_vector.cpp
@@ -85,7 +85,7 @@ StatusWith<std::vector<BSONObj>> splitVector(OperationContext* opCtx,
 
         // Allow multiKey based on the invariant that shard keys must be single-valued. Therefore,
         // any multi-key index prefixed by shard key cannot be multikey over the shard key fields.
-        IndexDescriptor* idx =
+        const IndexDescriptor* idx =
             collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx, keyPattern, false);
         if (idx == NULL) {
             return {ErrorCodes::IndexNotFound,
diff --git a/src/mongo/db/stats/storage_stats.cpp b/src/mongo/db/stats/storage_stats.cpp
index 45db0f8439c..ca4d68e310a 100644
--- a/src/mongo/db/stats/storage_stats.cpp
+++ b/src/mongo/db/stats/storage_stats.cpp
@@ -93,9 +93,9 @@ Status appendCollectionStorageStats(OperationContext* opCtx,
 
     std::unique_ptr<IndexCatalog::IndexIterator> it = indexCatalog->getIndexIterator(opCtx, false);
     while (it->more()) {
-        IndexCatalogEntry* entry = it->next();
-        IndexDescriptor* descriptor = entry->descriptor();
-        IndexAccessMethod* iam = entry->accessMethod();
+        const IndexCatalogEntry* entry = it->next();
+        const IndexDescriptor* descriptor = entry->descriptor();
+        const IndexAccessMethod* iam = entry->accessMethod();
         invariant(iam);
 
         BSONObjBuilder bob;
diff --git a/src/mongo/db/system_index.cpp b/src/mongo/db/system_index.cpp
index 1b7676b0596..8a5c3d93df2 100644
--- a/src/mongo/db/system_index.cpp
+++ b/src/mongo/db/system_index.cpp
@@ -169,7 +169,7 @@ Status verifySystemIndexes(OperationContext* opCtx) {
             invariant(indexCatalog);
 
             // Make sure the old unique index from v2.4 on system.users doesn't exist.
-            std::vector<IndexDescriptor*> indexes;
+            std::vector<const IndexDescriptor*> indexes;
             indexCatalog->findIndexesByKeyPattern(opCtx, v1SystemUsersKeyPattern, false, &indexes);
 
             if (!indexes.empty()) {
@@ -198,7 +198,7 @@ Status verifySystemIndexes(OperationContext* opCtx) {
             IndexCatalog* indexCatalog = collection->getIndexCatalog();
             invariant(indexCatalog);
 
-            std::vector<IndexDescriptor*> indexes;
+            std::vector<const IndexDescriptor*> indexes;
             indexCatalog->findIndexesByKeyPattern(opCtx, v3SystemRolesKeyPattern, false, &indexes);
             if (indexes.empty()) {
                 try {
diff --git a/src/mongo/db/transaction_participant.cpp b/src/mongo/db/transaction_participant.cpp
index 5929c41f752..6a5cab4eba2 100644
--- a/src/mongo/db/transaction_participant.cpp
+++ b/src/mongo/db/transaction_participant.cpp
@@ -219,7 +219,7 @@ void updateSessionEntry(OperationContext* opCtx, const UpdateRequest& updateRequ
                           << NamespaceString::kSessionTransactionsTableNamespace.ns(),
             idIndex);
 
-    auto indexAccess = collection->getIndexCatalog()->getIndex(idIndex);
+    auto indexAccess = collection->getIndexCatalog()->getEntry(idIndex)->accessMethod();
     // Since we are looking up a key inside the _id index, create a key object consisting of only
     // the _id field.
     auto idToFetch = updateRequest.getQuery().firstElement();
diff --git a/src/mongo/db/ttl.cpp b/src/mongo/db/ttl.cpp
index 99a1ef15a9c..0ad9cb0af35 100644
--- a/src/mongo/db/ttl.cpp
+++ b/src/mongo/db/ttl.cpp
@@ -207,7 +207,7 @@ private:
             return;
         }
 
-        IndexDescriptor* desc = collection->getIndexCatalog()->findIndexByName(opCtx, name);
+        const IndexDescriptor* desc = collection->getIndexCatalog()->findIndexByName(opCtx, name);
         if (!desc) {
             LOG(1) << "index not found (index build in progress? index dropped?), skipping "
                    << "ttl job for: " << idx;