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

[Pranith Kumar Karampuri]

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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