Index: clangd/ClangdLSPServer.h
===================================================================
--- clangd/ClangdLSPServer.h
+++ clangd/ClangdLSPServer.h
@@ -35,7 +35,7 @@
   /// for compile_commands.json in all parent directories of each file.
   ClangdLSPServer(JSONOutput &Out, const clangd::CodeCompleteOptions &CCOpts,
                   llvm::Optional<Path> CompileCommandsDir,
-                  const ClangdServer::Options &Opts);
+                  const ClangdServer::Options &Opts, bool CacheCompileCommands);
 
   /// Run LSP server loop, receiving input for it from \p In. \p In must be
   /// opened in binary mode. Output will be written using Out variable passed to
@@ -101,7 +101,8 @@
   // Various ClangdServer parameters go here. It's important they're created
   // before ClangdServer.
   DirectoryBasedGlobalCompilationDatabase NonCachedCDB;
-  CachingCompilationDb CDB;
+  // Can be null if no caching was requested.
+  std::unique_ptr<CachingCompilationDb> CachedCDB;
 
   RealFileSystemProvider FSProvider;
   /// Options used for code completion
Index: clangd/ClangdLSPServer.cpp
===================================================================
--- clangd/ClangdLSPServer.cpp
+++ clangd/ClangdLSPServer.cpp
@@ -12,6 +12,7 @@
 #include "JSONRPCDispatcher.h"
 #include "SourceCode.h"
 #include "URI.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Path.h"
@@ -133,7 +134,8 @@
   if (Params.metadata && !Params.metadata->extraFlags.empty()) {
     NonCachedCDB.setExtraFlagsForFile(File,
                                       std::move(Params.metadata->extraFlags));
-    CDB.invalidate(File);
+    if (CachedCDB)
+      CachedCDB->invalidate(File);
   }
 
   std::string &Contents = Params.textDocument.text;
@@ -157,7 +159,8 @@
     // fail rather than giving wrong results.
     DraftMgr.removeDraft(File);
     Server.removeDocument(File);
-    CDB.invalidate(File);
+    if (CachedCDB)
+      CachedCDB->invalidate(File);
     log(llvm::toString(Contents.takeError()));
     return;
   }
@@ -388,7 +391,8 @@
   if (Settings.compilationDatabasePath.hasValue()) {
     NonCachedCDB.setCompileCommandsDir(
         Settings.compilationDatabasePath.getValue());
-    CDB.clear();
+    if (CachedCDB)
+      CachedCDB->clear();
 
     reparseOpenedFiles();
   }
@@ -397,10 +401,15 @@
 ClangdLSPServer::ClangdLSPServer(JSONOutput &Out,
                                  const clangd::CodeCompleteOptions &CCOpts,
                                  llvm::Optional<Path> CompileCommandsDir,
-                                 const ClangdServer::Options &Opts)
-    : Out(Out), NonCachedCDB(std::move(CompileCommandsDir)), CDB(NonCachedCDB),
+                                 const ClangdServer::Options &Opts,
+                                 bool CacheCompileCommands)
+    : Out(Out), NonCachedCDB(std::move(CompileCommandsDir)),
+      CachedCDB(CacheCompileCommands
+                    ? llvm::make_unique<CachingCompilationDb>(NonCachedCDB)
+                    : nullptr),
       CCOpts(CCOpts), SupportedSymbolKinds(defaultSymbolKinds()),
-      Server(CDB, FSProvider, /*DiagConsumer=*/*this, Opts) {}
+      Server(CachedCDB ? (GlobalCompilationDatabase&) *CachedCDB : NonCachedCDB, FSProvider,
+             /*DiagConsumer=*/*this, Opts) {}
 
 bool ClangdLSPServer::run(std::FILE *In, JSONStreamStyle InputStyle) {
   assert(!IsDone && "Run was called before");
Index: clangd/tool/ClangdMain.cpp
===================================================================
--- clangd/tool/ClangdMain.cpp
+++ clangd/tool/ClangdMain.cpp
@@ -134,6 +134,12 @@
         "eventually. Don't rely on it."),
     llvm::cl::init(""), llvm::cl::Hidden);
 
+static llvm::cl::opt<bool> CacheCompilationArgs(
+    "cache-compilation-args",
+    llvm::cl::desc("When true, clangd will cache compilation arguments that "
+                   "come from the compilation databases."),
+    llvm::cl::init(false), llvm::cl::Hidden);
+
 int main(int argc, char *argv[]) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
   llvm::cl::ParseCommandLineOptions(argc, argv, "clangd");
@@ -235,7 +241,8 @@
   CCOpts.Limit = LimitResults;
 
   // Initialize and run ClangdLSPServer.
-  ClangdLSPServer LSPServer(Out, CCOpts, CompileCommandsDirPath, Opts);
+  ClangdLSPServer LSPServer(Out, CCOpts, CompileCommandsDirPath, Opts,
+                            CacheCompilationArgs);
   constexpr int NoShutdownRequestErrorCode = 1;
   llvm::set_thread_name("clangd.main");
   // Change stdin to binary to not lose \r\n on windows.