SERVER-42526 IndexBuildInterceptor should store KeyString keys

2 files changed, 49 insertions, 28 deletions

diff --git a/src/mongo/db/index/index_build_interceptor.cpp b/src/mongo/db/index/index_build_interceptor.cpp
index 510f275ce7b..a6a53894d1b 100644
--- a/src/mongo/db/index/index_build_interceptor.cpp
+++ b/src/mongo/db/index/index_build_interceptor.cpp
@@ -247,17 +247,20 @@ Status IndexBuildInterceptor::_applyWrite(OperationContext* opCtx,
                                           const InsertDeleteOptions& options,
                                           int64_t* const keysInserted,
                                           int64_t* const keysDeleted) {
-    const BSONObj key = operation["key"].Obj();
-    const RecordId opRecordId = RecordId(operation["recordId"].Long());
+    // Deserialize the encoded KeyString::Value.
+    int keyLen;
+    const char* binKey = operation["key"].binData(keyLen);
+    BufReader reader(binKey, keyLen);
+    const KeyString::Value keyString = KeyString::Value::deserialize(
+        reader,
+        _indexCatalogEntry->accessMethod()->getSortedDataInterface()->getKeyStringVersion());
+
     const Op opType =
         (strcmp(operation.getStringField("op"), "i") == 0) ? Op::kInsert : Op::kDelete;
 
-    KeyString::HeapBuilder keyString(
-        _indexCatalogEntry->accessMethod()->getSortedDataInterface()->getKeyStringVersion(),
-        key,
-        _indexCatalogEntry->ordering(),
-        opRecordId);
-    const KeyStringSet keySet{keyString.release()};
+    const KeyStringSet keySet{keyString};
+    const RecordId opRecordId =
+        KeyString::decodeRecordIdAtEnd(keyString.getBuffer(), keyString.getSize());
 
     auto accessMethod = _indexCatalogEntry->accessMethod();
     if (opType == Op::kInsert) {
@@ -398,6 +401,8 @@ Status IndexBuildInterceptor::sideWrite(OperationContext* opCtx,
         return Status::OK();
     }
 
+    // Reuse the same builder to avoid an allocation per key.
+    BufBuilder builder;
     std::vector<BSONObj> toInsert;
     for (const auto& keyString : keys) {
         // Documents inserted into this table must be consumed in insert-order.
@@ -405,9 +410,14 @@ Status IndexBuildInterceptor::sideWrite(OperationContext* opCtx,
         // other writes making up this operation are given. When index builds can cope with
         // replication rollbacks, side table writes associated with a CUD operation should
         // remain/rollback along with the corresponding oplog entry.
-        auto key = KeyString::toBson(keyString, _indexCatalogEntry->ordering());
-        toInsert.emplace_back(BSON("op" << (op == Op::kInsert ? "i" : "d") << "key" << key
-                                        << "recordId" << loc.repr()));
+
+        // Serialize the KeyString::Value into a binary format for storage. Since the
+        // KeyString::Value also contains TypeBits information, it is not sufficient to just read
+        // from getBuffer().
+        builder.reset();
+        keyString.serialize(builder);
+        BSONBinData binData(builder.buf(), builder.getSize(), BinDataGeneral);
+        toInsert.emplace_back(BSON("op" << (op == Op::kInsert ? "i" : "d") << "key" << binData));
     }
 
     if (op == Op::kInsert) {
@@ -415,12 +425,12 @@ Status IndexBuildInterceptor::sideWrite(OperationContext* opCtx,
         // document, to the index itself. Multikey information is never deleted, so we only need
         // to add this data on the insert path.
         for (const auto& keyString : multikeyMetadataKeys) {
-            auto key = KeyString::toBson(keyString, _indexCatalogEntry->ordering());
+            builder.reset();
+            keyString.serialize(builder);
+            BSONBinData binData(builder.buf(), builder.getSize(), BinDataGeneral);
             toInsert.emplace_back(BSON("op"
                                        << "i"
-                                       << "key" << key << "recordId"
-                                       << static_cast<int64_t>(
-                                              RecordId::ReservedId::kWildcardMultikeyMetadataId)));
+                                       << "key" << binData));
         }
     }
 
diff --git a/src/mongo/db/storage/key_string.h b/src/mongo/db/storage/key_string.h
index 404f4d9a30c..74fd5fd4d91 100644
--- a/src/mongo/db/storage/key_string.h
+++ b/src/mongo/db/storage/key_string.h
@@ -347,32 +347,43 @@ public:
      */
     std::string toString() const;
 
-    /// Members for Sorter
-    struct SorterDeserializeSettings {
-        SorterDeserializeSettings(Version version) : keyStringVersion(version) {}
-        Version keyStringVersion;
-    };
-
-    void serializeForSorter(BufBuilder& buf) const {
-        buf.appendNum(_ksSize);                                      // Serialize size of Keystring
-        buf.appendBuf(_buffer.get(), _ksSize);                       // Serialize Keystring
-        buf.appendBuf(_buffer.get() + _ksSize, _bufSize - _ksSize);  // Serialize Typebits
+    // Serializes this Value into a storable format with TypeBits information. The serialized
+    // format takes the following form:
+    //   [keystring size][keystring encoding][typebits encoding]
+    void serialize(BufBuilder& buf) const {
+        buf.appendNum(_ksSize);                  // Serialize size of Keystring
+        buf.appendBuf(_buffer.get(), _bufSize);  // Serialize Keystring + Typebits
     }
 
-    static Value deserializeForSorter(BufReader& buf, const SorterDeserializeSettings& settings) {
+    // Deserialize the Value from a serialized format.
+    static Value deserialize(BufReader& buf, KeyString::Version version) {
         const int32_t sizeOfKeystring = buf.read<LittleEndian<int32_t>>();
         const void* keystringPtr = buf.skip(sizeOfKeystring);
 
         BufBuilder newBuf;
         newBuf.appendBuf(keystringPtr, sizeOfKeystring);
 
-        auto typeBits = TypeBits::fromBuffer(settings.keyStringVersion, &buf);  // advances the buf
+        auto typeBits = TypeBits::fromBuffer(version, &buf);  // advances the buf
         if (typeBits.isAllZeros()) {
             newBuf.appendChar(0);
         } else {
             newBuf.appendBuf(typeBits.getBuffer(), typeBits.getSize());
         }
-        return {settings.keyStringVersion, sizeOfKeystring, newBuf.len(), newBuf.release()};
+        return {version, sizeOfKeystring, newBuf.len(), newBuf.release()};
+    }
+
+    /// Members for Sorter
+    struct SorterDeserializeSettings {
+        SorterDeserializeSettings(Version version) : keyStringVersion(version) {}
+        Version keyStringVersion;
+    };
+
+    void serializeForSorter(BufBuilder& buf) const {
+        serialize(buf);
+    }
+
+    static Value deserializeForSorter(BufReader& buf, const SorterDeserializeSettings& settings) {
+        return deserialize(buf, settings.keyStringVersion);
     }
 
     int memUsageForSorter() const {