Hi,
We made few changes in the design of the lease-locks as per the latest
discussion we had (thanks to everyone involved). Please find the details
in the below section and provide your comments.
http://www.gluster.org/community/documentation/index.php/Features/Upcall-infrastructure#delegations.2Flease-locks
In addition, (thanks to AFR team), we have formulated an approach to
filter out duplicate callback notifications.
http://www.gluster.org/community/documentation/index.php/Features/Upcall-infrastructure#Dependencies
<<<<
Filter-out duplicate notifications
Incase of replica bricks maintained by AFR/EC, the upcalls state is
maintained and processed on all the replica bricks. This will result in
duplicate notifications to be sent by all those bricks incase of
non-idempotent fops. Also in case of distributed volumes, cache
invalidation notifications on a directory entry will be sent by all the
bricks part of that volume. Hence We need support to filter out such
duplicate callback notifications.
The approach we shall take to address it is that,
add a new xlator on the client-side to track all the fops. Maybe
create a unique transaction id and send it to the server.
Server needs to store this transaction id in the client info as
part of upcall state.
While sending any notifications, add this transaction id too to the
request.
Client (the new xlator) has to filter out duplicate requests based
on the transaction ids received.
>>>>
Due to time-constraints, we may add the support to filter out duplicate
notifications in the subsequent releases of 3.7.
Below link contains the list of TODO items related to this feature -
http://www.gluster.org/community/documentation/index.php/Features/Upcall-infrastructure#TODO
Let me know if any of you are interested to work on any of those items.
Would be happy to assist you :)
Thanks,
Soumya
On 01/22/2015 02:31 PM, Soumya Koduri wrote:
Hi,
I have updated the feature page with more design details and the
dependencies/limitations this support has.
http://www.gluster.org/community/documentation/index.php/Features/Upcall-infrastructure#Dependencies
Kindly check the same and provide your inputs.
Few of them which may be addressed for 3.7 release are -
*AFR/EC*
- Incase of replica bricks maintained by AFR, the upcalls state is
maintained and processed on all the replica bricks. This will result in
duplicate notifications sent by all those bricks incase of
non-idempotent fops.
- Hence we need support on AFR to filter out such duplicate
callback notifications. Similar support is needed for EC as well.
- One of the approaches suggested by the AFR team is to cache the
upcall notifications received for around 1min (their current lifetime)
to detect & filter out the duplicate notifications sent by the replica
bricks.
*Cleanup during network disconnect - protocol/server*
- At present, incase of network disconnects between the
glusterfs-server and the client, the protocol/server looks up the fd
table associated with that client and sends 'flush' op for each of those
fds to cleanup the locks associated with it.
- We need similar support to flush the lease locks taken. Hence,
while granting the lease-lock, we plan to associate that upcall_entry
with the corresponding fd_ctx or inode_ctx so that they can be easily
tracked if needed to be cleaned up. Also it will help in faster lookup
of the upcall entries while trying to process the fops using the same
fd/inode.
Note: Above cleanup is done for the upcall state associated with only
lease-locks. For the other entries maintained (for eg:, for
cache-invalidations), the reaper thread (which will be used to cleanup
the expired entries in this xlator) will clean-up those states as well
once they get expired.
*Replay of the lease-locks state*
- At present, replay of locks by the client xlator (after network
disconnect and reconnect) seems to have been disabled.
- But when it is being enabled, we need to add support to replay
lease-locks taken as well.
- Till then, this will be considered as a limitation and will be
documented as suggested by KP.
Thanks,
Soumya
On 12/16/2014 09:36 AM, Krishnan Parthasarathi wrote:
- Is there a new connection from glusterfsd (upcall xlator) to
a client accessing a file? If so, how does the upcall xlator reuse
connections when the same client accesses multiple files, or
does it?
No. We are using the same connection which client initiates to send-in
fops. Thanks to you for pointing me initially to the 'client_t'
structure. As these connection details are available only in the server
xlator, I am passing these to upcall xlator by storing them in
'frame->root->client'.
- In the event of a network separation (i.e, a partition) between a
client
and a server, how does the client discover or detect that the
server
has 'freed' up its previously registerd upcall notification?
The rpc connection details of each client are stored based on its
client-uid. So incase of network partition, when client comes back
online, IMO it re-initiates the connection (along with new client-uid).
How would a client discover that a server has purged its upcall entries?
For instance, a client could assume that the server would notify it about
changes as before (while the server has purged the client's upcall
entries)
and assume that it still holds the lease/lock. How would you avoid that?
Please correct me if that's not the case. So there will new entries
created/added in this xlator. However, we still need to decide on how to
cleanup the old-timed-out and stale entries
* either clean-up the entries as and when we find any expired
entry or
stale entry (in case if notification fails).
* or by spawning a new thread which periodically scans through this
list and cleans up those entries.
There are couple of things to resource cleanup in this context.
1) Time to cleanup; For e.g, on expiry of a timer.
2) Order of cleaning up; This involves clearly establishing relationships
among inode, upcall entry and client_t(s). We should document this.
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