title: LMDB increase map_size
body: <p>I was working with LMDB++ (the C++ wrapper for LMDB) and I got this error:</p>
  
  <p><code>terminate called after throwing an instance of 'lmdb::map_full_error'
      what():  mdb_put: MDB_MAP_FULL: Environment mapsize limit reached
  </code></p>
  
  <p>Some googling told me that the default map_size is set low in LMDB. How do I go about increasing map_size?</p>