(ITS#7667) performance degradation when using MDB_INTEGERKEY

[romange@gmail.com]

Full_Name: Roman Gershman
Version: 
OS: linux 3.8.0-25-generic
URL: 
Submission from: (NULL) (212.150.97.210)


The program writes into mdb database 100 million key,value pairs.
All keys are 64bit integers.
If we open the new database with mdb_dbi_open(txn, NULL, 0, &dbi);
it has excellent performance - writes are done very quickly.

However if we open it with "mdb_dbi_open(txn, NULL, MDB_INTEGERKEY, &dbi)"
(and this is the only change in the code) its performance quickly deteriorates
and after it writes several million items to the clean db the difference in
write times becomes 2 orders of magnitude or even more compared to the previous
setting. 

We used the source from git repository git://gitorious.org/mdb/mdb.git at commit
id  214e9ed07d566307f22e16d0c1f1f57be9504a3b