On 06/03/2015 09:21 PM, fanghuang.data@xxxxxxxxx wrote:
On Wednesday, 3 June 2015, 19:43, "fanghuang.data@xxxxxxxxx" <fanghuang.data@xxxxxxxxx> wrote:
On Wednesday, 3 June 2015, 15:22, Xavier Hernandez <xhernandez@xxxxxxxxxx>
wrote:
On 06/03/2015 05:40 AM, Pranith Kumar Karampuri wrote:
On 06/02/2015 08:08 PM, fanghuang.data@xxxxxxxxx wrote:
Hi all,
As I reading the source codes of EC xlator, I am confused by the
cbk_list and answer_list defined in struct _ec_fop_data. Why do we
need two lists to combine the results of callback?
Especially for the answer_list, it is initialized
in ec_fop_data_allocate, then the nodes are added
in ec_cbk_data_allocate. Without being any accessed during the
lifetime of fop, the whole list finally is released in
ec_fop_cleanup.
Do I miss something for the answer_list?
+Xavi.
hi,
The only reason I found is that It is easier to cleanup cbks using
answers_list. You can check ec_fop_cleanup() function on latest master
to check how this is.
You are right. Currently answer_list is only used to cleanup all cbks
received while cbk_list is used to track groups of consistent answers.
Although currently doesn't happen, if error coercing or special
attribute handling are implemented, it could be possible that one cbk
gets referenced more than once in cbk_list, making answer_list
absolutely necessary.
That's a good point to put all the cbks into one group and put those with
consistent answers into the other group. But this designing policy cannot
be understood easily from the comments, source codes or the list names
(cbk_list,
answer_list). Could we rename the cbk_list to consist_list or something else
easier to be followed?
Combining of cbks is a bit involved until you
understand it but once you do, it is amazing. I tried to add comments
for this part of code and sent a patch, but we forgot to merge it :-)
http://review.gluster.org/9982. If you think we can add more
comments/change this part of code in a way it makes it easier, let us
know. We would love your feedback :-). Wait for Xavi's response as
well.
This patch is much clearer. For the function ec_combine_update_groups,
since we only operate on one list, should we use ec_combine_update_group? The
word "groups" is confusing for readers who may think there are two or
more groups.
I got it finally. The cbk-list actually maintains multi-groups of the same answer sorted
by the count. As Xavi said, one cbk may exist in different groups. So we need an
answer_list to do cleanup job. Pranith's patch explains it clearly. Well it is
really amazing.
Told ya! :-). I will resend the patch with updated comments about how
the groups work.
Pranith
--
Fang Huang
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