Re: GUADEC Hacking

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)



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