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Re: mdb database protected against any power cut?
Hallvard Breien Furuseth wrote:
> I wrote:
>> Francois Gnu writes:
>>> Is the mechanism of recovery mdb database working fine?
>> MDB needs no recovery. You may lose the last commit or two, but the
>> database will be consistent if the filesystem is correct.
> Whoops - to clarify: You may lose the _last_ one or two commits, until
> they get flushed to disk. The one in progress, and maybe the last
> successful commit. Not just any random commit:-)
> You can set up checkpointing to limit how long the last successful
> commit can be endangered. ...unless I read the code wrong. The
> manpage says "checkpoint" is only needed with "dbnosync". Hmm.
In the default mode (fully synchronous) you can only lose the in-progress
transaction. With dbnosync you can lose whatever hasn't been checkpointed yet.
There is another mode (recently added, not yet exposed in back-mdb) that only
flushes the data, not the metadata. With that mode, you might lose the
in-progress transaction and the immediately preceding commit. This mode is
slightly faster than fully-synchronous, and slightly slower than fully asynch.
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/