[Gluster-devel] break glusterd into small parts (Re: good job on fixing heavy hitters in spurious regressions)

[Kaushal M]

Modularising GlusterD is something we plan to do.  As of now, it's
just that a plan. We don't yet have a design to achieve it yet.

What Atin mentioned and what you've mentioned seem to be the same at a
high level. The core of GlusterD will be a co-ordinating engine, which
defines an interface for commands to use to do their work. The
commands will each be a seperate module implementing this interface.
Depending on how we implement, the actual names will be different.


On Sat, May 9, 2015 at 2:24 PM, Pranith Kumar Karampuri
<pkarampu at redhat.com> wrote:
>
> On 05/09/2015 02:21 PM, Atin Mukherjee wrote:
>>
>>
>> On 05/09/2015 01:36 PM, Pranith Kumar Karampuri wrote:
>>>
>>> On 05/09/2015 11:08 AM, Krishnan Parthasarathi wrote:
>>>>>
>>>>> Ah! now I understood the confusion. I never said maintainer should fix
>>>>> all the bugs in tests. I am only saying that they maintain tests, just
>>>>> like we maintain code. Whether you personally work on it or not, you at
>>>>> least have an idea of what is the problem and what is the solution so
>>>>> someone can come and ask you and you know the status of it. Expectation
>>>>> is not to fix every test failure that comes maintainer's way by
>>>>> maintainer alone. But he/she would know about problem/solution because
>>>>> he/she at least reviews it and merges it. We want to make sure that the
>>>>> tests are in good quality as well just like we make sure code is of
>>>>> good
>>>>> quality. Core is a special case. We will handle it separately.
>>>>
>>>> Glusterd is also a 'special' case. As a glusterd maintainer, I am
>>>> _not_ maintaining
>>>> <insert-your-favourite-gluster-command-here>'s implementation. So, I
>>>> don't
>>>> 'know'/'understand' how it has been implemented and by extension I
>>>> wouldn't be able
>>>> to fix it (forget maintaining it :-) ). Given the no. of gluster
>>>> commands, I won't be
>>>> surprised if I didn't have an inkling on how
>>>> <your-favourite-gluster-command> worked ;-)
>>>> I hope this encourages other contributors, i.e, any gluster (feature)
>>>> contributor,
>>>> to join Kaushal and me in maintaining glusterd.
>>>
>>> I understand the frustration kp :-). Human brain can only take so much.
>>> I think we are solving wrong problem by putting more people on the code.
>>> Why not break glusterd into small parts and distribute the load to
>>> different people? Did you guys plan anything for 4.0 for breaking
>>> glusterd?
>>> It is going to be a maintenance hell if we don't break it sooner.
>>>
>>> Glusterd does a lot of things: Lets see how we can break things up one
>>> thing at a time. I would love to spend some quality time thinking about
>>> this problem once I am done with ec work, but this is a rough idea I
>>> have for glusterd.
>>>
>>> 1) CLI handling:
>>> Glusterd-cli-xlator should act something like fuse in fs. It just gets
>>> the commands and passes it down, just like fuse gets the fops and passes
>>> it down. In glusterd process there should be snapshot.so, afr-cli.so,
>>> ec-cli.so, dht-cli.so loaded as management-xlators.
>>> Just like we have fops lets have mops (management operations).
>>> LOCK/STAGE/BRICK-OP/COMMIT-OP if there are more add them as well. Every
>>> time the top xlator in glusterd receives commands from cli, it converts
>>> the params into the arguments (req, op, dict etc) which are needed to
>>> carryout the cli. Now it winds the fop to all its children. One of the
>>> children is going to handle it locally, while the other child will send
>>> the cli to different glusterds that are in cluster. Second child of
>>> gluster-cli-xlator (give it a better name, but for now lets call it:
>>> mgmtcluster) will collate the responses and give the list of responses
>>> to glusterd-cli-xlator, it will call COLLATE mop on the first-child(lets
>>> call it local-handler) to collate the responses, i.e. logic for
>>> collating responses should also be in snapshot.so, afr-cli.so,
>>> dht-cli.so etc etc. Once the top translator does LOCK, STAGE, BRICK-OP,
>>> COMMIT-OP send response to CLI.
>>>
>>> 2) Volinfo should become more like inode_t in fs where each *-cli xlator
>>> can store their own ctx like snapshot-cli can store all snapshot related
>>> info for that volume in that context and afr can store afr-related info
>>> in the ctx. Volinfo data strcuture should have very minimal information.
>>> Maybe name, bricks etc.
>>>
>>> 3) Daemon handling:
>>>       Daemon-manager xlator should have MOPS like START/STOP/INFO and
>>> this xlator should be accessible for all the -cli xlators which want to
>>> do their own management of the daemons. i.e. ec-cli/afr-cli should do
>>> self-heal-daemon handling. dht should do rebalance process handling etc.
>>> to give an example:
>>> while winding START mop it has to specify the daemon as
>>> "self-heal-daemon" and give enough info etc.
>>>
>>> 4) Peer handling:
>>>      mgmtcluster(second child of top-xlator) should have MOPS like
>>> PEER_ADD/PEER_DEL/PEER_UPDATE etc to do the needful. top xlator is going
>>> to wind these operations based on the peer-cli-commands to this xlator.
>>>
>>> 5) volgen:
>>>      top xlator is going to wind MOP called GET_NODE_LINKS, which takes
>>> the type of volfile (i.e. mount/nfs/shd/brick etc) on which each *-cli
>>> will construct its node(s), stuff options and tell the parent xl-name to
>>> which it needs to be linked to. Top xlator is going to just link the
>>> nodes to construct the graph and does graph_print to generate the
>>> volfile.
>>>
>>> I am pretty sure I forgot some more aspects of what glusterd does but
>>> you get the picture right? Break each aspect into different xlator and
>>> have MOPS to solve them.
>>
>> Sounds interesting but needs to be thought out in details. For 4.0,wWe
>> do have a plan to make core glusterd algorithms work as a glusterd
>> engine and other features will work have interfaces to connect to it.
>> Your proposal looks another alternative. I would like to hear from the
>> community about it.
>
> Whatever works to reduce the burden on you folks :-).
>
> Pranith
>
>>> Pranith
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>>> Gluster-devel at gluster.org
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>
>
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