Open fails when using DB_DIRECT_DB

Question

Hi,
I'm trying to use the DB_DIRECT_DB flag to bypass the filesystem cache for some experiments I'm running (to clarify results, not for performance reasons). I'm using BDB 4.5.20 (C++ API) with kernel version 2.6.17-1.2142_FC4smp on Fedora Core 4.
I initialize a database handle as follows:
    Db* db = new Db(NULL, 0);
    db->set_cachesize(0, 1024*CACHE_SIZE, 1); // in kB
    DbEnv* env = db->get_env();
    env->set_flags(DB_DIRECT_DB, 1);
    env->set_msgfile(stderr);
    env->set_errfile(stderr);
    db->set_bt_compare(compare_int);
    db->open(NULL, file, NULL, DB_BTREE, 0, 0);The file already exists (was created by the same version of Berkeley DB, although without the O_DIRECT flag) and is 37MB on disk. Calling db->open generates this error:
read: 0x86735f0, 4096: Invalid argument
terminate called after throwing an instance of 'DbException'
  what():  Db::open: Invalid argumentThat address doesn't seem to be aligned to anything...
Without DB_DIRECT_DB, everything works. I've google'd around but can't find anything useful--I'd appreciate any suggestions!
Thanks,
Daniel

Answer 1

hello,
You may find the information in the following post helpful as
it is on a related issue with read() and DB_DIRECT_DB.
Bug: Specifying DB_DIRECT_DB crashes BDB 4.4.20
thanks,
Sandra