Launchpad itself

Bugs home page has inconsistent data due to caching

Bug #602936 reported by Paul Sladen
10
This bug affects 2 people
Affects Status Importance Assigned to Milestone
Launchpad itself
Fix Released
Low
Stuart Bishop
Launchpad itself 10.08

Bug Description

Malone will happily show self-inconsistent data (I thought I was hallucinating and doing things twice), but the screenshot confirms it:

  Number of New bugs: 0

and then happily lists half-a-dozen New bugs next to it!

Related branches

lp:~stub/launchpad/bug-602936-hotbug-caching
Robert Collins (community): Approve
Diff: 50 lines (+1/-21)
2 files modified
lib/lp/bugs/stories/bugs/xx-product-bugs-page.txt (+0/-18)
lib/lp/bugs/templates/bugtarget-bugs.pt (+1/-3)
Revision history for this message
Paul Sladen (sladen) wrote :
Revision history for this message
Paul Sladen (sladen) wrote :

And again, other way around now... more New bugs than what is being displayed...

Revision history for this message
Deryck Hodge (deryck) wrote :

Hi, Paul.

Thanks for the bug report!

The hot bugs list is cached, so there is a ten minute window in which changes are not reflected in the page. Bug 593054 is the general "we need cache invalidation" bug, but I think I'll keep this bug around about the specific issues here instead of duping. We could do some cheap fixes to cache the rest of the page, so at least the numbers are all in sync. It would still be mysterious why the page isn't updated, which is what Bug 593054 is about, but it might help slightly until that work gets in.

Cheers,
deryck

Changed in malone:
status: New → Triaged
importance: Undecided → Low
tags: added: caching trivial ui
summary: - Malone happily shows self-inconsistent data
+ Bugs home page has inconsistent data due to caching
Revision history for this message
Robert Collins (lifeless) wrote :

@deryck, cache invalidation being one of the two unsolved problems in computer science, might want to tackle the performance of the home page a different way :) - this isn't a good use of memcached because its hard for us to invalidate (impossible today) and users detect the skew trivially :(.

tags: added: memcache
removed: caching
Revision history for this message
Robert Collins (lifeless) wrote :

Bah, sorry for the out of line comment; I claim a long day + jetlag - please forgive me.

Revision history for this message
Deryck Hodge (deryck) wrote : Re: [Bug 602936] Re: Bugs home page has inconsistent data due to caching

On Wed, Aug 4, 2010 at 7:09 AM, Robert Collins
<email address hidden> wrote:
> Bah, sorry for the out of line comment; I claim a long day + jetlag -
> please forgive me.
>

No worries, all is cool. Thank you for the apology.

I know we've been chatting some on IRC, so just for the benefit of
others watching the bug...

I am happy to have this bit of caching turned off. I was under the
impression that the memcached infrastructure was evolving and that we
were looking to create some simple form of invalidation that would fix
this and other uses like this. If that work isn't or shouldn't be
done for a while, then we definitely don't want odd data when the
gains of memcached usage are not that high.

The caching of the hot bugs list was done initially as part of other
"the db is on fire!" work and was never meant as a replacement for
fixing other timeout issues.

Cheers,
deryck

Revision history for this message
Ursula Junque (ursinha) wrote : Bug fixed by a commit

Fixed in stable r11302 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/11302>.

tags: added: qa-needstesting
Ursula Junque (ursinha)
Changed in malone:
assignee: nobody → Stuart Bishop (stub)
milestone: none → 10.08
status: Triaged → Fix Committed
Stuart Bishop (stub)
tags: added: qa-untestable
removed: qa-needstesting
Julian Edwards (julian-edwards)
Changed in malone:
status: Fix Committed → Fix Released
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