On 27/05/15 09:00, sergej.jurecko@gmail.com wrote:

Using a dupsort and writing a large value (which is still bellow maxkeysize) will result in MDB_PAGE_FULL. (...) maxkeysize=10000

Too big MDB_MAXKEYSIZE. Its doc says: "Keys and MDB_DUPSORT data items must fit on a node in a regular page."

But the doc should clarify that MDB_MAXKEYSIZE can be set big enough to break lmdb.

Or mdb_env_open() can fail if the computed me_maxkey would be smaller.

Or compute a safe MIN_PAGESIZE from MDB_MAXKEYSIZE and use that, and then fail if the page size would be unsupported. (MIN_PAGESIZE can be computed at compile time, with some ugly macros.)

lmdb sets the max safe maxkeysize if you define MDB_MAXKEYSIZE=0. Some time ago, that was 1/3 of the size you could reasonably use (to allow 1 key + sub-page with 2 dupsort values), so it could make sense to define MDB_MAXKEYSIZE above the safe max. Today lmdb uses a sub-DB at once if a sub-page would be too small, though. So I don't see much need to support maxkeysize > safe max.