Re: best practices WRT resizing a MDB backend?

[Brian Reichert <reichert@numachi.com>]

On Thu, Aug 21, 2014 at 03:28:42PM -0700, Howard Chu wrote:
> maxsize is the back-mdb keyword. mapsize is the LMDB API property. They 
> both refer to the same thing. We used the word "maxsize" for back-mdb to 
> impress upon sysadmins that this really is a long-term maximum, and not a 
> setting that should be tuned on an ongoing basis.

Ok, that explains the terminology.

> >Can 'maxsize' ever be reduced after the fact?  If so, is their
> >guidance as to how much it can change (perhaps based on mdb_stat)?
> 
> Read the LMDB documentation.

What, this: http://symas.com/mdb/doc/ ?

A search for 'maxsize' or 'mapsize' yeilds no hits.

The mdb_stats manpage tells me how to invoke it, but not how to
interpret the results.  I have seen other messages to this mailing
list provide some guidance, but nothing that seemed to directly
apply to my questions.  Perhaps I'm missing some keyword somewhere.

> >My naive use of the LDMB backend has me assume the worst case, and
> >now everyone is equally punished for having a 'big' (albeit sparse)
> >database.
> 
> "Punished"? There is no penalty for configuring a large maxsize, no matter 
> how small the actual data.

The 'punishment' is multifold:

- consumption of diskspace for storage (our database is stored on
  the same partition as our backups; perhaps not the best of plans).
- the time it takes to compress/uncompress a backup.
- the network bandwidth cost of transmitting a file that's larger than
  it needs to be.

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

-- 
Brian Reichert				<reichert@numachi.com>
BSD admin/developer at large