Index: clang-tools-extra/trunk/clangd/index/Index.h
===================================================================
--- clang-tools-extra/trunk/clangd/index/Index.h
+++ clang-tools-extra/trunk/clangd/index/Index.h
@@ -116,8 +116,7 @@
 
   // The stored hash is truncated to RawSize bytes.
   // This trades off memory against the number of symbols we can handle.
-  // FIXME: can we reduce this further to 8 bytes?
-  constexpr static size_t RawSize = 16;
+  constexpr static size_t RawSize = 8;
   llvm::StringRef raw() const {
     return StringRef(reinterpret_cast<const char *>(HashValue.data()), RawSize);
   }
Index: clang-tools-extra/trunk/clangd/index/Serialization.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/index/Serialization.cpp
+++ clang-tools-extra/trunk/clangd/index/Serialization.cpp
@@ -300,7 +300,7 @@
 
 // REFS ENCODING
 // A refs section has data grouped by Symbol. Each symbol has:
-//  - SymbolID: 16 bytes
+//  - SymbolID: 8 bytes
 //  - NumRefs: varint
 //  - Ref[NumRefs]
 // Fields of Ref are encoded in turn, see implementation.
@@ -338,7 +338,7 @@
 // The current versioning scheme is simple - non-current versions are rejected.
 // If you make a breaking change, bump this version number to invalidate stored
 // data. Later we may want to support some backward compatibility.
-constexpr static uint32_t Version = 6;
+constexpr static uint32_t Version = 7;
 
 Expected<IndexFileIn> readRIFF(StringRef Data) {
   auto RIFF = riff::readFile(Data);
Index: clang-tools-extra/trunk/unittests/clangd/SerializationTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/SerializationTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/SerializationTests.cpp
@@ -27,7 +27,7 @@
 const char *YAML = R"(
 ---
 !Symbol
-ID: 057557CEBF6E6B2DD437FBF60CC58F35
+ID: 057557CEBF6E6B2D
 Name:   'Foo1'
 Scope:   'clang::'
 SymInfo:
@@ -53,7 +53,7 @@
 ...
 ---
 !Symbol
-ID: 057557CEBF6E6B2DD437FBF60CC58F36
+ID: 057557CEBF6E6B2E
 Name:   'Foo2'
 Scope:   'clang::'
 SymInfo:
@@ -72,7 +72,7 @@
 CompletionSnippetSuffix:    '-snippet'
 ...
 !Refs
-ID: 057557CEBF6E6B2DD437FBF60CC58F35
+ID: 057557CEBF6E6B2D
 References:
   - Kind: 4
     Location:
@@ -99,13 +99,13 @@
   ASSERT_TRUE(bool(ParsedYAML)) << ParsedYAML.takeError();
   ASSERT_TRUE(bool(ParsedYAML->Symbols));
   EXPECT_THAT(*ParsedYAML->Symbols,
-              UnorderedElementsAre(ID("057557CEBF6E6B2DD437FBF60CC58F35"),
-                                   ID("057557CEBF6E6B2DD437FBF60CC58F36")));
+              UnorderedElementsAre(ID("057557CEBF6E6B2D"),
+                                   ID("057557CEBF6E6B2E")));
 
   auto Sym1 = *ParsedYAML->Symbols->find(
-      cantFail(SymbolID::fromStr("057557CEBF6E6B2DD437FBF60CC58F35")));
+      cantFail(SymbolID::fromStr("057557CEBF6E6B2D")));
   auto Sym2 = *ParsedYAML->Symbols->find(
-      cantFail(SymbolID::fromStr("057557CEBF6E6B2DD437FBF60CC58F36")));
+      cantFail(SymbolID::fromStr("057557CEBF6E6B2E")));
 
   EXPECT_THAT(Sym1, QName("clang::Foo1"));
   EXPECT_EQ(Sym1.Signature, "");
@@ -131,7 +131,7 @@
   EXPECT_THAT(
       *ParsedYAML->Refs,
       UnorderedElementsAre(
-          Pair(cantFail(SymbolID::fromStr("057557CEBF6E6B2DD437FBF60CC58F35")),
+          Pair(cantFail(SymbolID::fromStr("057557CEBF6E6B2D")),
                testing::SizeIs(1))));
   auto Ref1 = ParsedYAML->Refs->begin()->second.front();
   EXPECT_EQ(Ref1.Kind, RefKind::Reference);