Re: LMDB crash after power failure

[Howard Chu <hyc@symas.com>]

Abilio Marques wrote:
> Hello,
> 
> I've successfully ported a particular piece of software from multiple plain files in disk to LMDB. There were multiple reasons to do so (i.e., performance and
> maintenance).
> 
> The program is making individual calls to a storage API, that in turn creates files or reads them (through a cache). There is no concept of transaction. For
> performance and lifetime reasons, the original code avoids to perform a fsync every time it writes to a file by queuing renames (for atomic writes) and deletes,
> which in turn are executed by a background thread after 2 seconds idling (or a max of 15 sec after first write/delete).
> 
> Replacing such a monster "files + cache" with LMDB was a breeze. I kept the API intact, and to deal with the price of fsyncs, I thought of opening with
> MDB_NOSYNC, and sync after 2 seconds of inactivity.

As documented, MDB_NOSYNC is only safe for power failure if the filesystem guarantees that it preserves the order of writes.
Otherwise all bets are off.

-- 
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/