Re: back-mdb locking strategies

[Howard Chu <hyc@symas.com>]

Howard Chu wrote:
> There are two main problems being addressed by the mdb approach - eliminating
> multiple layers of cache copying, and eliminating multiple layers of locking.
>
> Currently we have per-entry mutexes and also BDB locks for every cached item.
> The mutex overhead is ridiculous, 40-some bytes per mutex x 10 million entries
> is a lot of wasted storage. Especially since a single slapd can only actually
> lock 2-3 items per thread - i.e., we only need on the order of 100 locks,
> ever. The sane thing to do here is continue to use the BDB approach to
> locking, but with fewer options.

Note that we can use this locking approach in back-bdb too, but aside from the 
memory savings I don't see it giving any performance gain. The real gain comes 
from completely eliminating one layer of locks, not just from streamlining one 
layer but keeping both layers.

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