MultiGet support in ldb (#12283)

Summary:
While investigating test failures due to the inconsistency between `Get()` and `MultiGet()`, I realized that LDB currently doesn't support `MultiGet()`. This PR introduces the `MultiGet()` support in LDB. Tested the command manually. Unit test will follow in a separate PR.

Pull Request resolved: #12283

Test Plan:
When key not found
```
$> ./ldb --db=/data/users/jewoongh/rocksdb_test/T173992396/rocksdb_crashtest_blackbox --hex multi_get 0x0000000000000009000000000000012B00000000000002AB
Status for key 0x0000000000000009000000000000012B00000000000002AB: NotFound:
```
Compare the same key with get
```
$> ./ldb --db=/data/users/jewoongh/rocksdb_test/T173992396/rocksdb_crashtest_blackbox --hex get 0x0000000000000009000000000000012B00000000000002AB
Failed: Get failed: NotFound:
```

Multiple keys not found
```
$> ./ldb --db=/data/users/jewoongh/rocksdb_test/T173992396/rocksdb_crashtest_blackbox --hex multi_get 0x0000000000000009000000000000012B00000000000002AB 0x0000000000000009000000000000012B00000000000002AC                                                                                                                                                                                                        Status for key 0x0000000000000009000000000000012B00000000000002AB: NotFound:
Status for key 0x0000000000000009000000000000012B00000000000002AC: NotFound:
```

One of the keys found
```
$> ./ldb --db=/data/users/jewoongh/rocksdb_test/T173992396/rocksdb_crashtest_blackbox --hex multi_get 0x0000000000000009000000000000012B00000000000002AB 0x00000000000000090000000000000026787878787878
Status for key 0x0000000000000009000000000000012B00000000000002AB: NotFound:
0x22000000262724252A2B28292E2F2C2D32333031363734353A3B38393E3F3C3D02030001060704050A0B08090E0F0C0D12131011161714151A1B18191E1F1C1D
```

All of the keys found
```
$> ./ldb --db=/data/users/jewoongh/rocksdb_test/T173992396/rocksdb_crashtest_blackbox --hex multi_get 0x0000000000000009000000000000012B00000000000000D8 0x00000000000000090000000000000026787878787878                                                                                                                                                                                                            15:57:03
0x47000000434241404F4E4D4C4B4A494857565554535251505F5E5D5C5B5A595867666564636261606F6E6D6C6B6A696877767574737271707F7E7D7C7B7A797807060504030201000F0E0D0C0B0A090817161514131211101F1E1D1C1B1A1918
0x22000000262724252A2B28292E2F2C2D32333031363734353A3B38393E3F3C3D02030001060704050A0B08090E0F0C0D12131011161714151A1B18191E1F1C1D
```

Reviewed By: hx235

Differential Revision: D53048519

Pulled By: jaykorean

fbshipit-source-id: a6217905464c5f460a222e2b883bdff47b9dd9c7

tools/ldb_cmd.cc

@@ -208,6 +208,9 @@ LDBCommand* LDBCommand::SelectCommand(const ParsedParams& parsed_params) {
   if (parsed_params.cmd == GetCommand::Name()) {
     return new GetCommand(parsed_params.cmd_params, parsed_params.option_map,
                           parsed_params.flags);
+  } else if (parsed_params.cmd == MultiGetCommand::Name()) {
+    return new MultiGetCommand(parsed_params.cmd_params,
+                               parsed_params.option_map, parsed_params.flags);
   } else if (parsed_params.cmd == GetEntityCommand::Name()) {
     return new GetEntityCommand(parsed_params.cmd_params,
                                 parsed_params.option_map, parsed_params.flags);
@@ -2872,6 +2875,66 @@ void GetCommand::DoCommand() {
 
 // ----------------------------------------------------------------------------
 
+MultiGetCommand::MultiGetCommand(
+    const std::vector<std::string>& params,
+    const std::map<std::string, std::string>& options,
+    const std::vector<std::string>& flags)
+    : LDBCommand(options, flags, true,
+                 BuildCmdLineOptions({ARG_HEX, ARG_KEY_HEX, ARG_VALUE_HEX})) {
+  if (params.size() < 1) {
+    exec_state_ = LDBCommandExecuteResult::Failed(
+        "At least one <key> must be specified for multi_get.");
+  } else {
+    for (size_t i = 0; i < params.size(); ++i) {
+      std::string key = params.at(i);
+      keys_.emplace_back(is_key_hex_ ? HexToString(key) : key);
+    }
+  }
+}
+
+void MultiGetCommand::Help(std::string& ret) {
+  ret.append("  ");
+  ret.append(MultiGetCommand::Name());
+  ret.append(" <key_1> <key_2> <key_3> ...");
+  ret.append(" [--" + ARG_TTL + "]");
+  ret.append("\n");
+}
+
+void MultiGetCommand::DoCommand() {
+  if (!db_) {
+    assert(GetExecuteState().IsFailed());
+    return;
+  }
+  size_t num_keys = keys_.size();
+  std::vector<Slice> key_slices;
+  std::vector<PinnableSlice> values(num_keys);
+  std::vector<Status> statuses(num_keys);
+  for (const std::string& key : keys_) {
+    key_slices.emplace_back(key);
+  }
+  db_->MultiGet(ReadOptions(), GetCfHandle(), num_keys, key_slices.data(),
+                values.data(), statuses.data());
+
+  bool failed = false;
+  for (size_t i = 0; i < num_keys; ++i) {
+    if (statuses[i].ok()) {
+      fprintf(stdout, is_value_hex_ ? "0x%s\n" : "%s\n",
+              values[i].ToString(is_value_hex_).c_str());
+    } else {
+      fprintf(stderr, "Status for key %s: %s\n",
+              (is_key_hex_ ? StringToHex(keys_[i]) : keys_[i]).c_str(),
+              statuses[i].ToString().c_str());
+      failed = false;
+    }
+  }
+  if (failed) {
+    exec_state_ =
+        LDBCommandExecuteResult::Failed("one or more keys had non-okay status");
+  }
+}
+
+// ----------------------------------------------------------------------------
+
 GetEntityCommand::GetEntityCommand(
     const std::vector<std::string>& params,
     const std::map<std::string, std::string>& options,

tools/ldb_cmd_impl.h

@@ -403,6 +403,22 @@ class GetCommand : public LDBCommand {
   std::string key_;
 };
 
+class MultiGetCommand : public LDBCommand {
+ public:
+  static std::string Name() { return "multi_get"; }
+
+  MultiGetCommand(const std::vector<std::string>& params,
+                  const std::map<std::string, std::string>& options,
+                  const std::vector<std::string>& flags);
+
+  void DoCommand() override;
+
+  static void Help(std::string& ret);
+
+ private:
+  std::vector<std::string> keys_;
+};
+
 class GetEntityCommand : public LDBCommand {
  public:
   static std::string Name() { return "get_entity"; }