Berkeley DB Family

Hello!

I use BDB 4.5.20 and tried to use a DB_HASH access method providing my own hash function, since I have very specific keys. Keys are UUID, and they all have the same length (16 bytes) and specific binary representation which can be used to generate hash code. After I set own hash function using Db::set_h_hash() I get the call of this function during database open with a very strange data I was not expected.

Backtrace is:

storaged.dll!tbricks::storage::StorageBDBBackend::bdb_hash_func(Db * db=0x01dba398, const void * key=0x1318326c, unsigned int size=12) Line 35 C++
libdb45d.dll!_db_h_hash_intercept_c(__db * cthis=0x01dba418, const void * data=0x1318326c, unsigned int len=12) Line 483 + 0x97 bytes C++
libdb45d.dll!__ham_init_meta(__db * dbp=0x01dba418, hashmeta33 * meta=0x01dbb120, unsigned int pgno=0, _db_lsn * lsnp=0x0013f10c) Line 291 + 0x13 bytes C
libdb45d.dll!__ham_new_file(__db * dbp=0x01dba418, __db_txn * txn=0x01dbacc8, __fh_t * fhp=0x01dbafb8, const char * name=0x01dbac60) Line 402 + 0x13 bytes C
libdb45d.dll!__db_new_file(__db * dbp=0x01dba418, __db_txn * txn=0x01dbacc8, __fh_t * fhp=0x01dbafb8, const char * name=0x01dbac60) Line 284 + 0x15 bytes C
libdb45d.dll!__fop_file_setup(__db * dbp=0x01dba418, __db_txn * txn=0x01dba9e0, const char * name=0x01585624, int mode=384, unsigned int flags=129, unsigned int * retidp=0x0013f458) Line 586 + 0x42 bytes C
libdb45d.dll!__db_open(__db * dbp=0x01dba418, __db_txn * txn=0x01dba9e0, const char * fname=0x01585624, const char * dname=0x00000000, DBTYPE type=DB_HASH, unsigned int flags=129, int mode=0, unsigned int meta_pgno=0) Line 154 + 0x1d bytes C
libdb45d.dll!__db_open_pp(__db * dbp=0x01dba418, __db_txn * txn=0x01dba9e0, const char * fname=0x01585624, const char * dname=0x00000000, DBTYPE type=DB_HASH, unsigned int flags=129, int mode=0) Line 1079 + 0x23 bytes C
libdb45d.dll!Db::open(DbTxn * txnid=0x00000000, const char * file=0x01585624, const char * database=0x00000000, DBTYPE type=DB_HASH, unsigned int flags=33554561, int mode=0) Line 313 + 0x30 bytes C++
storaged.dll!tbricks::storage::BDBBackend::open_db(Db & db={...}, const char * fileName=0x01585624, DBTYPE dbType=DB_HASH) Line 372 + 0x21 bytes C++

Db::set_h_hash() documentation says nothing about behaviour like this.

Why BDB calls my hash function during database open while I do not put()/get() any data?

Firstly I was implemented hash function aborting the application if key length is not equal 16, because it looks like application internal error, and for sure application was aborted because of that.

How should I treat this data and do I have to return any hash code at all in this case?