Re: [openstack-dev] [Swift] 404 on geo-replicated clusters with write affinity

[Clay Gerrard]

Hi Bruno,

On Wed, May 17, 2017 at 3:47 PM, Bruno L  wrote:

>
> I see multiple bugs in launchpad that are related to this issue.
>

AFAIK, only one bug for this issue is still open, and has the most recent
thoughts added from the Forum

https://bugs.launchpad.net/swift/+bug/1503161

write a brief summary of the changes proposed,
>

I think the skinny of what's in the bug report is "make more backend DELETE
requests to handoffs".

Personally I was coming around to the idea that an explicit configurable
(i.e. similar to "request_node_count" for GET) would be easy to reason
about and give us a lot of flexibility (it would pair well per-policy
configuration WIP https://review.openstack.org/#/c/448240/).  It's possible
this could be implicit using some heuristic over the sort order of
primaries in the ring - but I think it'd be whole 'nother thing, and could
be added later as an "auto" sort of value for the option (i.e. workers =
[N|auto], or "replicas + 2" sort of syntax).

Additionally, it's been pointed out various times that collecting
X-Backend-Timestamp from the responses would allow for further reasoning
over the collected responses in addition to just the status codes (similar
to WIP for GET https://review.openstack.org/#/c/371150/ ) - but I'm
starting to think that'd be an enhancement to the extra handoff DELETE
requests rather than an complete alternative solution.

I don't think anyone really likes the idea of blindly translating a
majority 404 response on DELETE to 204 and calling it a win - so
unfortunately the fix is non-trival.  Glad to see you're interested in
getting your teeth into this one - let me know if there's anything I can do
to help!

Good Luck,

-Clay
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[openstack-dev] [Swift] 404 on geo-replicated clusters with write affinity

[Bruno L]

Hi everyone,

It was great to meet you at the Boston summit and agree on the best way to
fix the 404 error code bug on geo-replicated clusters with write affinity.

As you know, this is a topic that is dear to us at Catalyst, and we would
like to provide a patch to it. Since we are relatively new to the Swift
community, I'd like to ask for some guidance from the more experienced
developers, to ensure we are going in the right direction.

I see multiple bugs in launchpad that are related to this issue. Could we
agree which one we should use to progress with this?

Our discussion at the summit lead us to three ideas on how this could be
fixed. We decided we would combine two of them, to make sure all exceptions
and corner cases are covered. Could one of you (maybe Clay or John) write a
brief summary of the changes proposed, so we can use it as a specification
for our code changes?

Cheers,
Bruno
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