Hi Atin,
On 31/01/17 05:45, Atin Mukherjee wrote:
On Mon, Jan 30, 2017 at 9:02 PM, Xavier Hernandez <xhernandez@xxxxxxxxxx
<mailto:xhernandez@xxxxxxxxxx>> wrote:
Hi Atin,
On 30/01/17 15:25, Atin Mukherjee wrote:
On Mon, Jan 30, 2017 at 7:30 PM, Xavier Hernandez
<xhernandez@xxxxxxxxxx <mailto:xhernandez@xxxxxxxxxx>
<mailto:xhernandez@xxxxxxxxxx <mailto:xhernandez@xxxxxxxxxx>>>
wrote:
Hi,
I'm wondering how a new option needs to be created to be
available
to different versions of gluster.
When a new option is created for 3.7 for example, it needs
to have a
GD_OP_VERSION referencing the next 3.7 release. This ensures
that
there won't be any problem with previous versions.
However what happens with 3.8 ?
3.8.0 is greater than any 3.7.x, however the new option won't be
available until the next 3.8 release. How this needs to be
handled ?
I'd discourage to backport any new volume options from mainline
to the
stable releases branches like 3.7 & 3.8. This creates a lot of
backward
compatibility issues w.r.t clients. Any new option is actually
an RFE
and supposed to be slated for only upcoming releases.
Even if it's needed to solve an issue in all versions ?
For example, a hardcoded timeout is seen to be insufficient in some
configurations, so it needs to be increased, but increasing it will
be too much for many of the environments where the current timeout
has worked fine. It could even be not enough for other environments
still not tried, needed a future increase.
With a new option, this can be solved case by case and only when needed.
How can this be solved ?
Hi Xavi,
Let me try to explain this a bit in detail. A new option with an
op-version say 30721 (considering 3.7.21 is the next update of 3.7 which
is the oldest active branch) is introduced in mainline and then the same
is backported to 3.7 (slated for 3.7.21) & 3.8 branch (slated for
3.8.9). Now say if an user forms a cluster of three nodes with gluster
versions as 3.7.21, 3.8.9 & 3.8.8 respectively and tries to set this
option, volume set would always fail as in 3.8.8 this option is not
defined. Also any client running with 3.8 version would see a
compatibility issue here. Also the op-version number of the new option
has to be same across different release branches.
Thanks for the explanation. This confirms what I already thought. So the
question is: now that 3.10 has already been branched, does it mean that
any new option won't be available for LTS users until 3.12 is released ?
I think this is not acceptable, specially for changes intended to fix an
issue, not introducing new features.
With the current form of op-version management, I don't think this can
be solved, the only way is to ask users to upgrade to the latest.
As I said, someone using 3.10 LTS won't be able to upgrade until 3.12 is
released. What would we say to them when we add a new option to 3.11 ?
Maybe we should add a new kind of option that causes no failure if not
recognized. They are simply ignored. Many options do not cause any
visible functional change, so they could be defined even if some nodes
of the cluster don't recognize them (for example performance improvement
options or some timeout values).
Anyway, with the introduction of brick multiplexing, I think we should
reconsider how options are negotiated. I think that the op-version
infrastructure is not enough to handle multiplexed bricks because we
won't be able to upgrade a single volume that needs some new feature. We
would need to upgrade all volumes, including the clients, even if they
do not need anything new.
What do you think ?
Xavi
Kaushal - if you have any other ideas, please suggest.
Thanks,
Xavi
Thanks,
Xavi
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--
~ Atin (atinm)
--
~ Atin (atinm)
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