On Sun, Oct 18, 2009 at 3:56 AM, Theodore Tso <tytso@xxxxxxx> wrote:
> On Sat, Oct 17, 2009 at 11:26:04PM +0530, Viji V Nair wrote:
>> these files are not in a single directory, this is a pyramid
>> structure. There are total 15 pyramids and coming down from top to
>> bottom the sub directories and files are multiplied by a factor of 4.
>>
>> The IO is scattered all over!!!! and this is a single disk file system.
>>
>> Since the python application is creating files, it is creating
>> multiple files to multiple sub directories at a time.
>
> What is the application trying to do, at a high level? Sometimes it's
> not possible to optimize a filesystem against a badly designed
> application. :-(
The application is reading the gis data from a data source and
plotting the map tiles (256x256, png images) for different zoom
levels. The tree output of the first zoom level is as follows
/tiles/00
`-- 000
`-- 000
|-- 000
| `-- 000
| `-- 000
| |-- 000.png
| `-- 001.png
|-- 001
| `-- 000
| `-- 000
| |-- 000.png
| `-- 001.png
`-- 002
`-- 000
`-- 000
|-- 000.png
`-- 001.png
in each zoom level the fourth level directories are multiplied by a
factor of four. Also the number of png images are multiplied by the
same number.
>
> It sounds like it is generating files distributed in subdirectories in
> a completely random order. How are the files going to be read
> afterwards? In the order they were created, or some other order
> different from the order in which they were read?
The application which we are using are modified versions of mapnik and
tilecache, these are single threaded so we are running 4 process at a
time. We can say only four images are created at a single point of
time. Some times a single image is taking around 20 sec to create. I
can see lots of system resources are free, memory, processors etc
(these are 4G, 2 x 5420 XEON)
I have checked the delay in the backend data source, it is on a 12Gbps
LAN and no delay at all.
These images are also read in the same manner.
>
> With a sufficiently bad access patterns, there may not be a lot you
> can do, other than (a) throw hardware at the problem, or (b) fix or
> redesign the application to be more intelligent (if possible).
>
> - Ted
>
The file system is crated with "-i 1024 -b 1024" for larger inode
number, 50% of the total images are less than 10KB. I have disabled
access time and given a large value to the commit also. Do you have
any other recommendation of the file system creation?
Viji
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