Venkat Murty wrote:

Hi all, I am inserting a non-zero length key into a database where I provide a

compare function. But I am seeing that MDB_val->mv_size = 0 in the compare function. Is that possible?

If you saw it, then it must be possible...

Branch pages all start with an empty key.

More details (LMDB 0.9.11 Release):

I have a database where I want to delete all elements that have the same prefix.

void eraseElements (KeyPrefix prefix, MDB_txn *txn, MDB_dbi database) { MDB_val k;

k.mv_data = &prefix; k.mv_size = sizeof (KeyPrefix);

MDB_val v;

MDB_cursor *cur; mdb_cursor_open (txn, database, &cur); while (! mdb_cursor_get (cur, &k, &v, MDB_SET_RANGE))

This loop is rather inefficient. Should just initialize once with SET_RANGE, and then loop using NEXT.

{ if (memcmp (&prefix, k.mv_data, sizeof (KeyPrefix)) != 0) break; mdb_cursor_del (cur, 0);

     k.mv_data = &prefix;
     k.mv_size  = sizeof (KeyPrefix);
 }
 mdb_cursor_close (cur);

}

Relevant stack trace DB::compare (a, b) and b->mv_size == 0 mdb_cursor_set(mc, key, data, op=MDB_SET_RANGE, exactp=0x0) at mdb.c:5348 mdb_cursor_get(mc,key,data,op=MDB_SET_RANGE) at mdb.c:5655 eraseElements(..)