[Koha-devel] Cache::Memory must be removed (21955)

[Fridolin SOMERS]

Indeed, this is a big behavior error we found a few month ago.
I think we shared it in mailing but I can find how.
This is a big issue when you change an HTML systempreference like 
"opacnav", you see the change and when refresh its gone (you see the 
other plack worker).
We solved by installing memached everywhere.

Maybe we can just disable Cache::Memory when Plack mode is used.
Then I say we need a C4::Context->is_psgi() method :
https://bugs.koha-community.org/bugzilla3/attachment.cgi?id=76477

Programing is sometimes so wierd ;)

Regards,

Le 05/12/2018 à 20:20, Jonathan Druart a écrit :
> Hi devs,
> 
> I am still recovering from my holidays and I think I caught a quite big fish.
> 
> After an interesting track game I will explain why I am suggesting to
> remove Cache::Memory that is currently used as fallback for the L2
> cache.
> 
> What I tried to fix:
> Jenkins is complaining about selenium tests (regressions.t) failing on
> 18.05, it is a succession of events and bugs that were not linked at
> first glance.
> 
> Here are the different steps I went though:
> - On bug 21426 we noticed that USE_MEMCACHED was not taken into
> account. If set to "no" the default memcached config was defined in
> the koha-config.xml file anyway
> - A new regression selenium test was added on bug 21777 to catch the
> presence of an audio alert on the circulation page
> - Investigating the failing tests I noticed that koha-testing-docker
> was not setting the memcached config on the 18.05 branches (I guess
> the image has not been rebuilt yet)
> search_utf8.t output "Warning: script running in daemon mode, without
> recommended caching system (memcached)."
> - I also find that [% Koha.Preference('AudioAlerts') %] did not return
> the value set by the tests, but the value that the DB has before the
> tests were launched
> => It is a cache issue!
> - ...but only when memcached is not set...
> - Reading Koha::Cache->new we can notice that Cache::Memory is used
> for the L2 cache when memcached is not defined in the config
> 
> And so we have the problem: If a value is set in the cache by a Plack
> worker, it will not be available from another one, as the L2 cache is
> not shared (!)
> 
> To recreate easily the problem you can:
> - remove the memcached config
> - edit intranet-bottom.inc and add
> ===[% Koha.Preference('AudioAlerts') %]===
> - restart plack
> - Modify the value of AudioAlerts (using the UI)
> - Reload the page (reload several times if the value is still correct,
> it will depend on which worker will serve the request)
> 
> Solution:
> I am considering removing Cache::Memory unless somebody else has a better idea
> Bug 21955 - Cache::Memory should not be used as L2 cache
> 
> Note that it should not affect a lot of people as everybody is
> supposed to have memcached configured and working correctly!
> 
> Cheers,
> Jonathan
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> 

-- 
Fridolin SOMERS <fridolin.somers at biblibre.com>
BibLibre, France - software and system maintainer