Bigstrings are used to transfer the raw serialised data into and out of the database. They may point directly to a memory-mapped region of the database file.

Flags describing the (sorting) properties of keys and values of a map.

make ~serialise ~deserialise creates a converter from a serialising and a deserialising function

• parameter serialise

  serialise alloc x may call alloc len once to allocate a bigstring of size len. It then must fill the serialised data of x into this bigstring and return exactly this bigstring. If serialise didn't call alloc it may return any bigstring. alloc may return uninitialised memory. It is therefore recommended that serialise overwrites all allocated memory to avoid leaking possibly sensitive memory content into the database.

If serialise calls alloc the library may utilise the MDB_RESERVE interface when appropriate to avoid calls to malloc and memcpy.

• parameter deserialise

  The passed bigstring is only valid as long as the current transaction. It is therefore strongly recommended not to leak it out of deserialise.

• parameter flags

  Flags to be set on a map using this converter.

Depending on the use of a converter as key or value Map.create and Map.open_existing will select the correct set of flags: _key flags will be used for keys and _dup flags will be used for values on maps supporting duplicates.

The bigstring converter returns bigstrings as returned by the lmdb backend. These bigstrings point into the environment memory-map and are therefore only guaranteed to be valid until the transaction ends. If you need longer-lived values then use the string converter, make a copy or write a custom converter.

The string converter simply copies the raw database content from / to OCaml strings.