20170713.md

MongoDB

How to discover the storage engine

Using mongo shell

> db.serverStatus().storageEngine
> db.runCommand({serverStatus: 1}).storageEngine

Programmatically

g++ main.cpp -g3 -std=c++14 -I/usr/include/mongocxx/v_noabi -I/usr/include/bsoncxx/v_noabi -I/usr/include/libbson-1.0 -lbsoncxx -lmongocxx
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <mongocxx/uri.hpp>

#include <bsoncxx/json.hpp>
#include <bsoncxx/types.hpp>
#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
#include <iostream>

/**
 * this code was written to discover which storage engine the mongodb instance
 * is using
 */
int main (int argc, char** argv)
{
  if (argc < 2)
  {
    std::cout << "[bin] [dbName]" << std::endl;
    return 1;
  }

  try
  {
    std::string dbName(argv[1]);

    mongocxx::instance instance{};
    mongocxx::client conn{ mongocxx::uri{} };

    auto db = conn[dbName];

    // server status
    auto serverStatusComm = bsoncxx::builder::basic::document{};
    serverStatusComm.append(bsoncxx::builder::basic::kvp("serverStatus", 1));
    auto resp = db.run_command(serverStatusComm.view()).view();

    auto engine = resp["storageEngine"];
    std::string engineName(engine["name"].get_utf8().value);

    // print storageEngine document
    std::cout << bsoncxx::to_json(engine) << std::endl;

    std::cout << "This instance is running with '";
    std::cout << engineName << "' storage engine" << std::endl;
  }
  catch (const std::exception& e)
  {
    std::cout << e.what() << std::endl;
  }
}

References

• New C++ Mongo driver: how to see type and how to get string value
• check storage engine from shell