Btrfs devel - Oct 2013 - question

when i read transaction_kthread function in disk-io.c 

delay = HZ * 30;

why commit transaction is 30 seconds,  Other values 20 seconds,10 seconds?
what considerations about the commit transaction interval?


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On Sun, Oct 20, 2013 at 11:19:26PM +0800, lilofile
wrote:
> 
> when i read transaction_kthread function in disk-io.c 
> 
> delay = HZ * 30;
> 
> why commit transaction is 30 seconds,  Other values 20 seconds,10 seconds?
> what considerations about the commit transaction interval?
   It''s a more or less arbitrary number. There''s been a patch
recently
(last couple of months) to allow modifying the value. If you make it
too large, you end up using lots of RAM for unflushed changes, you
risk losing those changes if the machine crashes. If you make it too
small, you end up writing lots more metadata, because that''s always
changing as the FS is modified.

   Hugo.

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