Re: Disk cache

On Apr 9, 2006, at 17:21, Felipe Magno de Almeida wrote:
> > Is there any points having a cache at all?
>
> IMHO, it is only possible to answer this with tests and see how better
> a cache could perform the I/O operations.
> I believe that other assumption could be that rarest blocks could stay
> in cache longer too, since they should be requested more often from
> peers.

Yes. But usually there isn't a single piece which is rarest, but a  
whole bunch of them. But a read cache should probably prioritize  
them, assuming all peers implement rarest-first.

> FWIW, Boost reviewed and accepted asio, a library for asynchronous
> I/O. It supports only sockets operations for now, but probably soon it
> will support files as well, which could have some impact in easy of
> use and CPU usage.

Yes, I'm following this progress. I'm already using asio for  
networking (not in the main branch yet, but soon).

> BitComet has this statistics in one torrent I'm downloading:
>
> Disk Read Statistics:  Request: 38982 (freq: 2.1/s), Actual Disk Read:
> 2542 (freq: 0.1/s), Hit Ratio: 93.4%
> Disk Write Statistics: Request: 9986 (freq: 1.2/s), Actual Disk Write:
> 184 (freq: 0.0/s), Hit Ratio: 98.1%
>
> It seems like pretty good numbers. Although we cant really know what
> Disk Write means here...

Yeah, I'm a bit interested in how that cache works as well. The stats  
for the read cache seems to suggest that either almost the entire  
torrent fits in the cache, or that the swarm is practically  
requesting the same pieces all the time.

--
Arvid Norberg




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