report a path, make it restartable

arangod/RocksDBEngine/RocksDBEngine.cpp

@@ -92,7 +92,15 @@ void RocksDBEngine::validateOptions(std::shared_ptr<options::ProgramOptions>) {}
 
 // preparation phase for storage engine. can be used for internal setup.
 // the storage engine must not start any threads here or write any files
-void RocksDBEngine::prepare() {}
+void RocksDBEngine::prepare() {
+  // get base path from DatabaseServerFeature
+  auto databasePathFeature =
+      application_features::ApplicationServer::getFeature<DatabasePathFeature>(
+          "DatabasePath");
+  _basePath = databasePathFeature->directory();
+  
+  TRI_ASSERT(!_basePath.empty());
+}
 
 void RocksDBEngine::start() {
   // it is already decided that rocksdb is used
@@ -342,7 +350,7 @@ int RocksDBEngine::getViews(TRI_vocbase_t* vocbase,
 }
 
 std::string RocksDBEngine::databasePath(TRI_vocbase_t const* vocbase) const {
-  return std::string();  // no path to be returned here!
+  return _basePath;
 }
 
 std::string RocksDBEngine::collectionPath(TRI_vocbase_t const* vocbase,

arangod/RocksDBEngine/RocksDBEngine.h

@@ -260,6 +260,7 @@ class RocksDBEngine final : public StorageEngine {
   rocksdb::Options _options;
   std::unique_ptr<RocksDBComparator> _cmp;
   std::string _path;
+  std::string _basePath;
 
   std::unique_ptr<RocksDBCounterManager> _counterManager;
 };

js/server/upgrade-database.js

@@ -94,10 +94,7 @@
     constant2name[DATABASE_EXISTING] = 'existing';
 
     // path to version file
-    let versionFile;
-    if (internal.db._path()) {
-      versionFile = internal.db._path() + '/VERSION';
-    }
+    let versionFile = internal.db._path() + '/VERSION';
 
     // all defined tasks
     const allTasks = [];
@@ -287,7 +284,7 @@
           lastTasks[task.name] = true;
 
           // save/update version info
-          if (isLocal && versionFile) {
+          if (isLocal) {
             fs.write(
               versionFile,
               JSON.stringify({
@@ -303,7 +300,7 @@
       }
 
       // save file so version gets saved even if there are no tasks
-      if (isLocal && versionFile) {
+      if (isLocal) {
         fs.write(
           versionFile,
           JSON.stringify({
@@ -350,7 +347,7 @@
       }
 
       // VERSION file exists, read its contents
-      if (versionFile && fs.exists(versionFile)) {
+      if (fs.exists(versionFile)) {
         var versionInfo = fs.read(versionFile);
 
         if (versionInfo === '') {
@@ -490,7 +487,7 @@
           return false;
         }
 
-        if (db._engine().name != "rocksdb") {
+        if (db._engine().name !== "rocksdb") {
           users.ensureIndex({
             type: 'hash',
             fields: ['user'],