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

[Atin Mukherjee]

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.
> 
> Pranith
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-- 
~Atin