Persistent data » History » Revision 12
Revision 11 (Greg Burri, 09/07/2009 05:35 PM) → Revision 12/18 (Greg Burri, 09/07/2009 05:36 PM)
h1. Persistent data
h2. Files cache
This file contains all the shared files and theirs SHA-1 hashes. This file is saved in user space after an update of the file list, it is completely loaded at the start of Aybabtu. If some paths of some files doesn't match the shared directory they are discarded.
This file is saved as a binary file serialized by protocol buffer.
You can see the proto file here : source:/application/Protos/files_cache.proto
h3. Size
Here is a size approximation for 50'000 files stored in 1 TB. The overhead of the file format is not taken in account.
<pre>
Nb of files : 50'0000
Total size : 1 TB
Chunk Size : 32 MB
Average file per directory : 50
Average filename and dirname length : 50 char
Size of a hash : 20B
</pre>
<pre>
AverageFileSize = 1*1024^4 / 50'000 = 21MB
Sha1Size = floor(AverageFileSize / 32MB) * 20 * 50'000 = 1 * 20 * 50'000 = 977kB
FilenameSize = 50'000 * 50 * 2 = 4.8MB (2 bytes per char)
DirnameSize = (50'000 / 50) * 50 * 2 = 97kB
TotalSize = 977kB + 4.8MB + 97kB = 5.9MB
</pre>
h2. Queued files and directories
A file containing the queued files and directories is saved in user space. An item from the list may contains a remote peer id and/or the hashes which identify a file.
As the file cache file (see above), this file is saved as a binary file serialized by protocol buffer.
For more details see the file : source:/application/Protos/queue.proto
h2. Configuration file
here are the persisted data :
* The nick
* The shared folders in read-only
* The shared folders in read-write
* Core address and password for remote core
There is two ways to persist theses data :
# Using of _QSettings_ : http://doc.trolltech.com/4.5/qsettings.html
# Using a custom file containing data serialized with _Protocol Buffer_ as the file cache
h3. Pros for the first method (_QSettings_)
* Easier to create, not necessary to create a file definition.
* Standard to Qt.
h3. Pros for the second method (_Protocol Buffer_)
* Same method as the two other files.
* All the persisted data is in the same place.