Re: (ITS#9027) LMDB: API to retrieve map address

[hyc@symas.com]

github@nicwatson.org wrote:
> Full_Name: Nic Watson
> Version: 
> OS: Linux
> URL: ftp://ftp.openldap.org/incoming/
> Submission from: (NULL) (73.132.68.128)
> 
> 
> Goal:
> I'd like a clean way to get at the address of the data memory map in LMDB.
> 
> MDB_envinfo.me_mapaddr only returns the map address if MAP_FIXED is used.
> 
> Current Workarounds:
> * Use OS-specific mechanism to retrieve all memory maps (e.g.
> /proc/<pid>/smaps). 
> * Defeat opaque handle and reach into the MDB_env struct directly and grab the
> me_map field.
> 
> Justification:
> In my current application, I notice a significant performance increase if I
> mlock the mapfile.  In order to do that cleanly, I need the address of the map.

That sounds odd. Is there a lot of memory pressure from other processes on the machine?
Where is the performance loss or gain coming from?

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