Re: GUADEC Hacking

[Jamie McCracken <jamiemcc blueyonder co uk>]

Matthias Clasen wrote:
> On Mon, 2005-04-11 at 18:21 +0100, Jamie McCracken wrote:
>
> > The culprit is pretty obviously GConf which is why I'm glad DConf is 
> > considering having a DB backend to address this. The short term fixes 
> > which Havoc has already suggested (moving the schema crap sideways and 
> > possibly mmap'ing some things) should cut some of that down but only a 
> > properly indexed database will give you both speed and memory efficiency 
> > (mmap'ing stuff is obviously wasteful memory wise).
>
>
> mmapping normally saves memory, since you can share the map between all
> apps, and only actually needed pages are in ram. The only thing wasted
> by a big mmap cache is address space, which is cheap.

Not really comparable to a DB which is designed for the cases where you 
need good random access performance but cant afford to bung it all in 
memory.

EG if you have a million records in GConf you will end up with a pretty 
large mutli megagbyte chunk of memory being allocated.

With a DB, random access to indexed keys is really quick and for most 
DBs you can tell it how much memory to use to cache the pages. The 
result is the most frequently used keys end up in the cache rather than 
all the keys if you mmap. The performance difference between the two is 
mostly neglible (assuming you will get a 90% cache hit ratio on your DB 
which should be possible if you allocate the right amount of cache)

jamie.

> Matthias