Adding gluster-devel.
On 03/06/2014 01:15 PM, Krishnan Parthasarathi wrote:
All,
In recent discussions around design (and implementation) of the barrier
feature, couple of things came to light.
1) changelog xlator needs barrier xlator to block unlink and rename FOPs
in the call path. This is apart from the current list of FOPs that are
blocked
in their call back path.
This is to make sure that the changelog has a bounded queue of unlink and
rename FOPs,
from the time barriering is enabled, to be drained, committed to changelog
file and published.
2) It is possible in a pure distribute volume that the following sequence of
FOPs could result
in snapshots of bricks disagreeing on inode type for a file or directory.
t1: snap b1
t2: unlink /a
t3: mkdir /a
t4: snap b2
where, b1 and b2 are bricks of a pure distribute volume V.
The above sequence can happen with the current barrier xlator design, since we
allow unlink FOPs
to go through to the disk and only block their acknowledgement to the
application. This implies
a concurrent mkdir on the same name could succeed, since DHT doesn't serialize
unlink and mkdir FOPs,
unlike AFR.
Avati,
I hear that you have a solution for problem 2). Could you please start the
discussion on this thread?
It would help us to decide how to go about with the barrier xlator
implementation.
thanks,
Krish
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