I have completed the patches and pushed for reviews. Please feel free to raise your review concerns/suggestions.

https://review.gluster.org/#/c/glusterfs/+/21868 <https://www.google.com/url?q=https%3A%2F%2Freview.gluster.org%2F%23%2Fc%2Fglusterfs%2F%2B%2F21868&sa=D&ust=1547360636897000&usg=AFQjCNFBLolUmZYRP05J_7GbdYXGSs_Wcg>

https://review.gluster.org/#/c/glusterfs/+/21907 <https://www.google.com/url?q=https%3A%2F%2Freview.gluster.org%2F%23%2Fc%2Fglusterfs%2F%2B%2F21907&sa=D&ust=1547360636897000&usg=AFQjCNFT0DYFibCGY_n8a3JdF53-5L1Jrw>

https://review.gluster.org/#/c/glusterfs/+/21960 <https://www.google.com/url?q=https%3A%2F%2Freview.gluster.org%2F%23%2Fc%2Fglusterfs%2F%2B%2F21960&sa=D&ust=1547360636897000&usg=AFQjCNEZUnX5MjDJNvowrRNQzIjnGX-Skg>

https://review.gluster.org/#/c/glusterfs/+/21989/ <https://www.google.com/url?q=https%3A%2F%2Freview.gluster.org%2F%23%2Fc%2Fglusterfs%2F%2B%2F21960&sa=D&ust=1547360636897000&usg=AFQjCNEZUnX5MjDJNvowrRNQzIjnGX-Skg>


Rafi KC

On 12/24/18 3:58 PM, RAFI KC wrote:

On 12/21/18 6:56 PM, Sankarshan Mukhopadhyay wrote:
On Fri, Dec 21, 2018 at 6:30 PM RAFI KC <rkavu...@redhat.com> wrote:
Hi All,

What is the problem?
As of now self-heal client is running as one daemon per node, this means
even if there are multiple volumes, there will only be one self-heal
daemon. So to take effect of each configuration changes in the cluster,
the self-heal has to be reconfigured. But it doesn't have ability to
dynamically reconfigure. Which means when you have lot of volumes in the cluster, every management operation that involves configurations changes
like volume start/stop, add/remove brick etc will result in self-heal
daemon restart. If such operation is executed more often, it is not only
slow down self-heal for a volume, but also increases the slef-heal logs
What is the value of the number of volumes when you write "lot of
volumes"? 1000 volumes, more etc

Yes, more than 1000 volumes. It also depends on how often you execute glusterd management operations (mentioned above). Each time self heal daemon is restarted, it prints the entire graph. This graph traces in the log will contribute the majority it's size.

How to fix it?

We are planning to follow a similar procedure as attach/detach graphs
dynamically which is similar to brick multiplex. The detailed steps is
as below,

1) First step is to make shd per volume daemon, to generate/reconfigure
volfiles per volume basis .

    1.1) This will help to attach the volfiles easily to existing shd daemon

    1.2) This will help to send notification to shd daemon as each
volinfo keeps the daemon object

    1.3) reconfiguring a particular subvolume is easier as we can check
the topology better

    1.4) With this change the volfiles will be moved to workdir/vols/

2) Writing new rpc requests like attach/detach_client_graph function to
support clients attach/detach

    2.1) Also functions like graph reconfigure, mgmt_getspec_cbk has to
be modified

3) Safely detaching a subvolume when there are pending frames to unwind.

    3.1) We can mark the client disconnected and make all the frames to
unwind with ENOTCONN

    3.2) We can wait all the i/o to unwind until the new updated subvol

4) Handle scenarios like glusterd restart, node reboot, etc

At the moment we are not planning to limit the number of heal subvolmes
per process as, because with the current approach also for every volume
heal was doing from a single process. We have not heared any major
complains on this?
Is the plan to not ever limit or, have a throttle set to a default
high(er) value? How would system resources be impacted if the proposed
design is implemented?

The plan is to implement in a way that it can support more than one multiplexed self-heal daemon. The throttling function as of now returns the same process to multiplex, but it can be easily modified to create a new process.

This multiplexing logic won't utilize any additional resources that it currently does.

Rafi KC

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