[PATCHES] Convert gencache to dbwrap to enable mutexes

[Stefan (metze) Metzmacher]

Am 24.06.2014 22:22, schrieb Christof Schmitt:
> On Tue, Jun 24, 2014 at 12:43:54PM -0700, Christof Schmitt wrote:
>> On Sat, Jun 21, 2014 at 10:20:44AM +0200, Stefan (metze) Metzmacher wrote:
>>> Hi Christof,
>>>
>>>>> While having a look at it I may found a problem with mutexes and ctdb.
>>>>>
>>>>>         /* only pass through specific flags */
>>>>>         tdb_flags &= TDB_SEQNUM|TDB_VOLATILE;
>>>>>
>>>>> in db_open_ctdb() seems to completely useless (or wrong).
>>>>> ctdbd_db_attach() is called before and gets the raw value of tdb_flags.
>>>>> It has only has effect for
>>>>>
>>>>>         db_ctdb->wtdb = tdb_wrap_open(db_ctdb, db_path, hash_size,
>>>>>                                       lpcfg_tdb_flags(lp_ctx, tdb_flags),
>>>>>                                       O_RDWR, 0);
>>>>>
>>>>> So I think we can just remove tdb_flags &= TDB_SEQNUM|TDB_VOLATILE; above
>>>>> and let lpcfg_tdb_flags() remove TDB_MUTEX_LOCKING when adding TDB_NOMMAP.
>>>>
>>>> The two patches at the end of the changeset implement those changes.
>>>
>>> Thanks! I'll try an autobuild on a machine with mutex support next week.
>>
>> I just discovered another issue. gencache opens databases with CLEAR_IF_FIRST.
>> That is not allowed with mutexes and it also triggers a warning in dbwrap when
>> transactions are being used.
>>
>> The easiest option would be using dbwrap only for gencache_notrans.tdb and
>> removing CLEAR_IF_FIRST for that database. For gencache.tdb, i am not sure how
>> to handle the case when tdb_check fails without CLEAR_IF_FIRST.
> 
> Sorry for the confusion. CLEAR_IF_FIRST has to be set for mutexes. The
> main issue is that transactions are not allowed in dbwrap if
> CLEAR_IF_FIRST is set. My idea here is to adapt dwrap to only warn if
> the database has been opened through db_open which allows the clustered
> usage. Databases opened directly with dbwrap_local_open should still
> allow transactions and CLEAR_IF_FIRST.

Transactions are not allowed with mutexes if I remember correctly.

metze