add create_column_family and drop_column_family cmd to ldb tool (#5503)

Summary:
`create_column_family` cmd already exists but was somehow missed in the help message.
also add `drop_column_family` cmd which can drop a cf without opening db.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5503

Test Plan: Updated existing ldb_test.py to test deleting a column family.

Differential Revision: D16018414

Pulled By: lightmark

fbshipit-source-id: 1fc33680b742104fea86b10efc8499f79e722301

tools/ldb_cmd.cc

@@ -223,6 +223,10 @@ LDBCommand* LDBCommand::SelectCommand(const ParsedParams& parsed_params) {
     return new CreateColumnFamilyCommand(parsed_params.cmd_params,
                                          parsed_params.option_map,
                                          parsed_params.flags);
+  } else if (parsed_params.cmd == DropColumnFamilyCommand::Name()) {
+    return new DropColumnFamilyCommand(parsed_params.cmd_params,
+                                         parsed_params.option_map,
+                                         parsed_params.flags);
   } else if (parsed_params.cmd == DBFileDumperCommand::Name()) {
     return new DBFileDumperCommand(parsed_params.cmd_params,
                                    parsed_params.option_map,
@@ -1125,6 +1129,44 @@ void CreateColumnFamilyCommand::DoCommand() {
   CloseDB();
 }
 
+void DropColumnFamilyCommand::Help(std::string& ret) {
+  ret.append("  ");
+  ret.append(DropColumnFamilyCommand::Name());
+  ret.append(" --db=<db_path> <column_family_name_to_drop>");
+  ret.append("\n");
+}
+
+DropColumnFamilyCommand::DropColumnFamilyCommand(
+    const std::vector<std::string>& params,
+    const std::map<std::string, std::string>& options,
+    const std::vector<std::string>& flags)
+  : LDBCommand(options, flags, true, {ARG_DB}) {
+  if (params.size() != 1) {
+    exec_state_ = LDBCommandExecuteResult::Failed(
+        "The name of column family to drop must be specified");
+  } else {
+    cf_name_to_drop_ = params[0];
+  }
+}
+
+void DropColumnFamilyCommand::DoCommand() {
+  auto iter = cf_handles_.find(cf_name_to_drop_);
+  if (iter == cf_handles_.end()) {
+    exec_state_ = LDBCommandExecuteResult::Failed(
+        "Column family: " + cf_name_to_drop_ + " doesn't exist in db.");
+    return;
+  }
+  ColumnFamilyHandle* cf_handle_to_drop = iter->second;
+  Status st = db_->DropColumnFamily(cf_handle_to_drop);
+  if (st.ok()) {
+    fprintf(stdout, "OK\n");
+  } else {
+    exec_state_ = LDBCommandExecuteResult::Failed(
+        "Fail to drop column family: " + st.ToString());
+  }
+  CloseDB();
+}
+
 // ----------------------------------------------------------------------------
 
 namespace {

tools/ldb_cmd_impl.h

@@ -205,6 +205,23 @@ class CreateColumnFamilyCommand : public LDBCommand {
   std::string new_cf_name_;
 };
 
+class DropColumnFamilyCommand : public LDBCommand {
+ public:
+  static std::string Name() { return "drop_column_family"; }
+
+  DropColumnFamilyCommand(const std::vector<std::string>& params,
+                          const std::map<std::string, std::string>& options,
+                          const std::vector<std::string>& flags);
+
+  static void Help(std::string& ret);
+  virtual void DoCommand() override;
+
+  virtual bool NoDBOpen() override { return false; }
+
+ private:
+  std::string cf_name_to_drop_;
+};
+
 class ReduceDBLevelsCommand : public LDBCommand {
  public:
   static std::string Name() { return "reduce_levels"; }

tools/ldb_test.py

@@ -553,8 +553,10 @@ class LDBTestCase(unittest.TestCase):
                          "1")
         self.assertRunOK("get cf3_1 --column_family=three",
                          "3")
+        self.assertRunOK("drop_column_family three", "OK")
         # non-existing column family.
         self.assertRunFAIL("get cf3_1 --column_family=four")
+        self.assertRunFAIL("drop_column_family four")
 
     def testIngestExternalSst(self):
         print "Running testIngestExternalSst..."

tools/ldb_tool.cc

@@ -82,6 +82,8 @@ void LDBCommandRunner::PrintHelp(const LDBOptions& ldb_options,
   DBLoaderCommand::Help(ret);
   ManifestDumpCommand::Help(ret);
   ListColumnFamiliesCommand::Help(ret);
+  CreateColumnFamilyCommand::Help(ret);
+  DropColumnFamilyCommand::Help(ret);
   DBFileDumperCommand::Help(ret);
   InternalDumpCommand::Help(ret);
   RepairCommand::Help(ret);