Index: clang-tools-extra/trunk/clangd/index/SymbolCollector.h
===================================================================
--- clang-tools-extra/trunk/clangd/index/SymbolCollector.h
+++ clang-tools-extra/trunk/clangd/index/SymbolCollector.h
@@ -60,6 +60,9 @@
     bool CountReferences = false;
     /// The symbol ref kinds that will be collected.
     /// If not set, SymbolCollector will not collect refs.
+    /// Note that references of namespace decls are not collected, as they
+    /// contribute large part of the index, and they are less useful compared
+    /// with other decls.
     RefKind RefFilter = RefKind::Unknown;
     /// If set to true, SymbolCollector will collect all refs (from main file
     /// and included headers); otherwise, only refs from main file will be
Index: clang-tools-extra/trunk/clangd/index/SymbolCollector.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/index/SymbolCollector.cpp
+++ clang-tools-extra/trunk/clangd/index/SymbolCollector.cpp
@@ -367,7 +367,7 @@
     return true;
   if (!shouldCollectSymbol(*ND, *ASTCtx, Opts))
     return true;
-  if (CollectRef &&
+  if (CollectRef && !isa<NamespaceDecl>(ND) &&
       (Opts.RefsInHeaders || SM.getFileID(SpellingLoc) == SM.getMainFileID()))
     DeclRefs[ND].emplace_back(SpellingLoc, Roles);
   // Don't continue indexing if this is a mere reference.
Index: clang-tools-extra/trunk/unittests/clangd/SymbolCollectorTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/SymbolCollectorTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/SymbolCollectorTests.cpp
@@ -443,6 +443,8 @@
   };
   class $bar[[Bar]];
   void $func[[func]]();
+
+  namespace $ns[[NS]] {} // namespace ref is ignored
   )");
   Annotations Main(R"(
   class $bar[[Bar]] {};
@@ -474,6 +476,7 @@
                                   HaveRanges(Main.ranges("bar")))));
   EXPECT_THAT(Refs, Contains(Pair(findSymbol(Symbols, "func").ID,
                                   HaveRanges(Main.ranges("func")))));
+  EXPECT_THAT(Refs, Not(Contains(Pair(findSymbol(Symbols, "NS").ID, _))));
   // Symbols *only* in the main file (a, b, c) had no refs collected.
   auto MainSymbols =
       TestTU::withHeaderCode(SymbolsOnlyInMainCode.code()).headerSymbols();