Avoid create directory for every column families (#6358)

Summary:
A relatively recent regression causes for every CF, create and open directory is called for the DB directory, unless CF has a private directory. This doesn't scale well with large number of column families.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6358

Test Plan: Run all existing tests and see it pass. strace with db_bench --num_column_families and observe it doesn't open directory for number of column families.

Differential Revision: D19675141

fbshipit-source-id: da01d9216f1dae3f03d4064fbd88ce71245bd9be

db/column_family.cc

@@ -1320,17 +1320,26 @@ Env::WriteLifeTimeHint ColumnFamilyData::CalculateSSTWriteHint(int level) {
                             static_cast<int>(Env::WLTH_MEDIUM));
 }
 
-Status ColumnFamilyData::AddDirectories() {
+Status ColumnFamilyData::AddDirectories(
+    std::map<std::string, std::shared_ptr<Directory>>* created_dirs) {
   Status s;
+  assert(created_dirs != nullptr);
   assert(data_dirs_.empty());
   for (auto& p : ioptions_.cf_paths) {
-    std::unique_ptr<Directory> path_directory;
-    s = DBImpl::CreateAndNewDirectory(ioptions_.env, p.path, &path_directory);
-    if (!s.ok()) {
-      return s;
+    auto existing_dir = created_dirs->find(p.path);
+
+    if (existing_dir == created_dirs->end()) {
+      std::unique_ptr<Directory> path_directory;
+      s = DBImpl::CreateAndNewDirectory(ioptions_.env, p.path, &path_directory);
+      if (!s.ok()) {
+        return s;
+      }
+      assert(path_directory != nullptr);
+      data_dirs_.emplace_back(path_directory.release());
+      (*created_dirs)[p.path] = data_dirs_.back();
+    } else {
+      data_dirs_.emplace_back(existing_dir->second);
     }
-    assert(path_directory != nullptr);
-    data_dirs_.emplace_back(path_directory.release());
   }
   assert(data_dirs_.size() == ioptions_.cf_paths.size());
   return s;

db/column_family.h

@@ -497,7 +497,10 @@ class ColumnFamilyData {
 
   Env::WriteLifeTimeHint CalculateSSTWriteHint(int level);
 
-  Status AddDirectories();
+  // created_dirs remembers directory created, so that we don't need to call
+  // the same data creation operation again.
+  Status AddDirectories(
+      std::map<std::string, std::shared_ptr<Directory>>* created_dirs);
 
   Directory* GetDataDir(size_t path_id) const;
 
@@ -589,7 +592,7 @@ class ColumnFamilyData {
   std::atomic<uint64_t> last_memtable_id_;
 
   // Directories corresponding to cf_paths.
-  std::vector<std::unique_ptr<Directory>> data_dirs_;
+  std::vector<std::shared_ptr<Directory>> data_dirs_;
 };
 
 // ColumnFamilySet has interesting thread-safety requirements

db/db_impl/db_impl.cc

@@ -2301,7 +2301,8 @@ Status DBImpl::CreateColumnFamilyImpl(const ColumnFamilyOptions& cf_options,
       auto* cfd =
           versions_->GetColumnFamilySet()->GetColumnFamily(column_family_name);
       assert(cfd != nullptr);
-      s = cfd->AddDirectories();
+      std::map<std::string, std::shared_ptr<Directory>> dummy_created_dirs;
+      s = cfd->AddDirectories(&dummy_created_dirs);
     }
     if (s.ok()) {
       single_column_family_mode_ = false;

db/db_impl/db_impl.h

@@ -826,7 +826,6 @@ class DBImpl : public DB {
                      std::vector<ColumnFamilyHandle*>* handles, DB** dbptr,
                      const bool seq_per_batch, const bool batch_per_txn);
 
-
   static Status CreateAndNewDirectory(Env* env, const std::string& dirname,
                                       std::unique_ptr<Directory>* directory);
 

db/db_impl/db_impl_open.cc

@@ -454,8 +454,9 @@ Status DBImpl::Recover(
     s = CheckConsistency();
   }
   if (s.ok() && !read_only) {
+    std::map<std::string, std::shared_ptr<Directory>> created_dirs;
     for (auto cfd : *versions_->GetColumnFamilySet()) {
-      s = cfd->AddDirectories();
+      s = cfd->AddDirectories(&created_dirs);
       if (!s.ok()) {
         return s;
       }