[Tilesathome] Proposal: Keeping tileset as one file

Michael Bergbauer listsub-osm at noname.franken.de
Mon Jun 9 11:43:57 BST 2008


On Mon Jun 09, 2008 at 12:0506PM +0200, spaetz wrote:
> On Mon, Jun 09, 2008 at 10:31:19AM +0200, Jiri Klement wrote:
> > Btw. Is tilesets unzipping done on hdd or ramdisc? Using ramdisc
> > should improve performance a bit without extra effort.
>  
> It's unzipped to the disk partition where the tiles are. So the final 
> mv to their end destination is cheap. Unzipping into RAM disk and 
> then moving them to the partition were equally expensive. We had 
> tried a RAM disk before on the dev server.

I had a look at the code recently, and I was quite surprised that the
unzipping is already done on the NFS storage and not locally. I'm not
sure if there wouldn't be a speedup when unzipping and doing the
verification of the tileset locally - as you (at least) save a few NFS
round trips when going through all files in the directory - and as far
as I remember, this is done a few times.

When doing this stuff on local disks, there wouldn't be much difference
when doing the extraction into a ram disk and operation on the files
there compared to extracting the files to the correct volume and doing
the necessary there. Directory Entries are held in the I/O cache of the
system and therefore, it's regardless whether the files are in a ram
disk or on a real disk. However, I would expect the system to send out
NFS requests to the server, when the same operation happens on a NFS
mount (because the nfs client *can't* know the directory didn't change!)
and therefore, this operation should be slower than local or ram disks. 

I wasn't able to do a verification of this theory so far, and it wouldn't
be a big speedup, but we're currently on the limit, so everything can
help. 


-- 
Michael Bergbauer <michael at noname.franken.de>

Munich, Germany




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