Re: Pre-approval request for dpkg sync() changes for squeeze

[Goswin von Brederlow <goswin-v-b@web.de>]

Phillip Susi <psusi@cfl.rr.com> writes:

> On 10/22/2010 5:35 AM, Guillem Jover wrote:
>>   1) Switch back from sync() to fsync() before rename() (while keeping
>
> Don't you WANT to use sync?  If you fsync every file that is going to be
> rather slow since it forces a disk write for every file, rather than
> allowing writes between each file to be combined and batched.  Ideally
> you want to unpack all files from all packages being installed/upgraded,
> then issue one big sync(), and finally all of the rename()s, with one
> final sync(), don't you?
>
> To throw out some numbers, it seems like it can easily take 60ms or more
> for an fsync(), between writing the file data, writing the journal,
> writing inode, writing the directory entry, then finally the journal
> again.  If you are replacing 1000 files then you are spending 60 seconds
> just on the fsync calls.  If you only use a single sync, then the whole
> thing could easily write all of the file data, adjacent inodes, journal
> commits, etc in 1-2 seconds with only 2-3 seeks.

Or 5 minutes because sync() also needs to write out the 16GB cache data
to my usb 1.0 drive that is not involved with dpkg at all.

MfG
        Goswin