On 19/08/15 15:57, Niels de Vos wrote:
On Tue, Aug 18, 2015 at 04:51:58PM +0530, Jiffin Tony Thottan wrote:
Comments inline.
On 18/08/15 09:54, Niels de Vos wrote:
On Mon, Aug 17, 2015 at 06:20:50PM +0530, Anoop C S wrote:
Hi all,
As we move forward, in order to fix the limitations with current trash
translator we are planning to replace the existing criteria for trashed
files inside trash directory with a general flat hierarchy as described
in the following sections. Please have your thoughts on following
design considerations.
Current implementation
======================
* Trash translator resides on glusterfs server stack just above posix.
* Trash directory (.trashcan) is created during volume start and is
visible under root of the volume.
* Each trashed file is moved (renamed) to trash directory with an
appended time stamp in the file name.
* Exact directory hierarchy (w.r.t the root of volume) is maintained
inside trash directory whenever a file is deleted/truncated from a
directory
Outstanding issues
==================
* Since renaming occurs at the server side, client-side is unaware of
trash doing rename or create operations.
* As a result files/directories may not be visible from mount point.
This might be something upcall could help with. If the trash xlator is
placed above upcall, any clients interested in the .trashcan directory
(or subdirs) could get an in/revalidation request.
* Files/Directories created from from trash translator will not have
gfid associated with it until lookup is performed.
When a client receives an invalidation of the parent directory (from
upcall), a LOOKUP will follow on the next request.
If I understand it correctly , solution become more complex if integrate
both translator and upcall together.
1.) Upcall notification can be send to a client only if it has accessed
.trashcan
Correct, and those are the only clients we care about. Clients that do
not have the .trashcan directory entries cached do not need to
invalidate that cache.
2.) There should be translator at client side to initiate lookup after
receiving upcall notification
No, that is not needed. A LOOKUP will happen when the directory/inode
needs a revalidate. After an invalidate from upcall, the next revalidate
will cause a LOOKUP.
3.) Performance hit. Say file `foo`is present in a/b/c/. We need to create
path a/b/c/ inside trash directory.
So ideally trash xlator will first create directory 'a' , then send upcall
notification to all of the client and then clients will initiate lookup on
'a',
perform gfid healing on that directory. After that it will create `b` and
repeat the same procedure.
Yes, directories are more tricky. But I think this is still a better
approach then renaming a file to include the full path.
Proposed Flat hierarchy
=======================
I'm missing a bit of info here, what limitations need to be addressed?
all above mentioned outstanding issues can be addressed by the flat
hierarchy.
But you also introduce new issues. A huge directory to browse would be
major concern. Users like doing directory listings and that is one of
the worst workloads we have on Gluster :-/
* Instead of creating the whole directory under trash, we will rename
the file and place it directly under trash directory (of course with
appended time stamp).
* Directory hierarchy can be stored via either of the following two
approaches:
(a) File name will contain the whole path with time stamp
appended
(b) Store whole hierarchy as an xattr
If this is needed, definitely go with (b). Filenames have a limit, and
the full path (directories + filename + timestamp) could surely hit
that.
Thanks for the suggestion.
Other enhancements
==================
Have these been filed as bugs/RFEs? If not, please do so and include a
good description of the work that is needed. Maybe others in the Gluster
community are interested in providing patches, and details on what to do
is very helpful.
Sure. We will file different RFE's as soon as possible and sent it in
different mail.
Thanks!
The RFEs opened for trash xlator are listed below :
1.) https://bugzilla.redhat.com/show_bug.cgi?id=1264847 - flat
hierarchy for files inside trash directory
2.) https://bugzilla.redhat.com/show_bug.cgi?id=1264849 - Create trash
directory only when its is enabled
3.) https://bugzilla.redhat.com/show_bug.cgi?id=1264853 - trash helper
translator at client-side
4.) https://bugzilla.redhat.com/show_bug.cgi?id=1264857 - Restore
operation for files under trash directory
Contributions are mostly welcome.
With Regards,
Jiffin
Thanks,
Niels
* Create the trash directory only
when trash xlator is enabled.
* Operations such as unlink, rename etc
will be prevented on trash
directory only when trash xlator is
enabled.
* A new trash helper translator on client side(loaded only when
trash
is enabled) to resolve split brain issues with truncation of
files.
* Restore files from trash with the help of an explicit setfattr
call.
Thanks & Regards,
-Anoop C S
-Jiffin Tony Thottan
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Jiffin
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