Re: LMDB mmap usage

[Kristoffer Sjögren <stoffe@gmail.com>]

I'm not looking for fairies :-) I was just curious exactly how mmap
interacts with the OS in order to understand performance metrics
better.

On Sat, Feb 6, 2016 at 5:46 PM, Howard Chu <hyc@symas.com> wrote:
> Kristoffer Sjögren wrote:
>>
>> Thanks Howard. What's the best documentation on mmap you know, aside
>> from read kernel source code?
>
>
> Not sure what you're asking. Read the mmap(2) manpage and its related pages.
> If you're thinking there's something fancy hidden in there for you to take
> advantage of, I don't think you should be using mmap in the first place.
>
>
>> On Fri, Feb 5, 2016 at 10:33 PM, Howard Chu <hyc@symas.com> wrote:
>>>
>>> Kristoffer Sjögren wrote:
>>>>
>>>>
>>>> Hi
>>>>
>>>> Our application do lots of caching using vmtouch, up to a point where
>>>> there isn't a lot of memory left on the machine. We would like to use
>>>> LMDB on the same machine to store around 40GiB data of a few hundred
>>>> million entries.
>>>>
>>>> How can we best understand the interaction and behavior of the OS
>>>> cache and sharing of memory between processes? Is LMDB doing something
>>>> to help the OS?
>>>
>>>
>>>
>>> Nope, LMDB does nothing special with its mmap.
>>>
>>> --
>>>    -- Howard Chu
>>>    CTO, Symas Corp.           http://www.symas.com
>>>    Director, Highland Sun     http://highlandsun.com/hyc/
>>>    Chief Architect, OpenLDAP  http://www.openldap.org/project/
>>
>>
>
>
> --
>   -- Howard Chu
>   CTO, Symas Corp.           http://www.symas.com
>   Director, Highland Sun     http://highlandsun.com/hyc/
>   Chief Architect, OpenLDAP  http://www.openldap.org/project/