[389-devel] RFC: New Design: Fine Grained ID List Size

[David Boreham]

On 9/14/2013 12:44 PM, Howard Chu wrote:
> Ah totally forgot about that, it's been a couple years since I looked 
> inside that code. LMDB updates record counts on every write op so 
> returning the count is zero-cost. (Ironically we don't use this fact 
> to optimize filter evaluation order in OpenLDAP. Probably should...) 
> Also due to the fact that writing a leaf page requires every page up 
> to the root to be updated (copy-on-write design), updating the counts 
> also comes "for free" since the root page had to be updated anyway. 
> (Or put another way, LMDB writes are already slow by design; updating 
> the counters doesn't make them any slower.) 

BDB has a similar feature. We're just having a little trouble finding it ;)