#defineMDB_FIXEDMAP0x01
mmap at a fixed address (experimental)
#defineMDB_NOSUBDIR0x4000
no environment directory
#defineMDB_NOSYNC0x10000
don't fsync after commit
#defineMDB_RDONLY0x20000
read only
#defineMDB_NOMETASYNC0x40000
don't fsync metapage after commit
#defineMDB_WRITEMAP0x80000
use writable mmap
#defineMDB_MAPASYNC0x100000
use asynchronous msync when MDB_WRITEMAP is used
#defineMDB_NOTLS0x200000
tie reader locktable slots to MDB_txn objects instead of to threads
#defineMDB_NOLOCK0x400000
don't do any locking, caller must manage their own locks
#defineMDB_NORDAHEAD0x800000
don't do readahead (no effect on Windows)
#defineMDB_NOMEMINIT0x1000000
don't initialize malloc'd memory before writing to datafile