Object Cache + Memcached Breaks website

  • Resolved dev

    (@devksec)


    4 years, 1 month ago

    Hello,

    So we have a multisite setup (2 woocommerce subsites) with total cache which works fine using DB caching + memcached. When we disabled DB caching and try enable object caching instead, it breaks the backend of the WP sites which only responds with timeouts. The frontend seems to work fine however.

    Initially when this issue occurred we performed a manual clean remove/reinstall of total cache and just enabling object cache (with nothing else enabled) caused the issue to reoccur.

    We’ve restored our old settings and all works fine but only without object cache being enabled. The memcache server connection test, from within the object cache settings, passes and the settings are default.

    Any idea what could be causing enabling object caching to break the backend or are there some extra steps within the switch over that need to be completed ?

    Many Thanks!

Viewing 5 replies - 16 through 20 (of 20 total)
  • Plugin Contributor Marko Vasiljevic

    (@vmarko)

    Hello @devksec

    Thank you for the info. Sorry for the late reply I was trying to check more about this.
    The plugin can detect a connection issue with Memcached, and again, the issue happens in the back-end. This is strange because as per your configuration "objectcache.enabled_for_wp_admin": false, so the object cache should not be used there. So it’s a very strange issue.
    You can try inspecting what is being cached using memcached-tool, and maybe add to the Non-persistent groups in the settings, to exclude unwanted items.
    Thanks!

    Thread Starter dev

    (@devksec)

    No worries, thank you for your support.

    So when enabling object crashing eventually the whole multisite goes down not just the wordpress backend. This is where we start to see the issue before eventually the whole site does. A reboot of the server nor services brings it back and requires for it to be disabled within the master.php.

    We’ve been using memcached tools to check the contents. This is how we know with the previous RDS config pagecache had some data chunks in there and could confirm DB caching works correctly now with the RDS changes.

    Thread Starter dev

    (@devksec)

    So we’ve given it another go and the results were as follows:

    1.Disabled DB caching & enabled object caching.
    2. 2000+ objects with about 150Mb new usage on memcache. Cleared all caches
    3. 404 error pages on products, pages & blogs but not home page (Affects all subsites)
    4. Reset permalinks on one subsite but backend started to time out.
    5. Noticed some pages being accessible but then front & back end started to timeout on all sites. (steps 1-5 were over a 30/40 min period.)
    6. Restarted apache + phpfpm
    7. 404s on pages,products etc again on all subsites
    8. slow loading & timeouts on front-backend again
    9. left for 10~mins and total of 2500~ items in memcache with 200mbs mem used. Site still unusable and 404 pages on front end apart from homepage
    10. disabled object caching via master.php & restart apache + php-fpm
    11. 404 errors now on wordpress backend custom login pages & front end
    12. full cache clear
    13. reboot of services again as 404 issues not resolve
    14. reboot of memcache server

    Trying to now recover the site but no better to finding out what is causing it.

    Thread Starter dev

    (@devksec)

    Ithemes security (hide login) had to be disabled before we could gain access to WP backend and restore of the .htaccess file

    Not sure what caused the .htaccess file to break in the process but something removed the default wordpress lines.

    • This reply was modified 4 years, 1 month ago by dev.
    Plugin Contributor Marko Vasiljevic

    (@vmarko)

    Hello @devksec

    Thank you for the information. As I can see it’s best not to use Object Cache. The only thing I can offer you is our Professional support in Performance>Support so we can investigate the compatibility issue.
    The issue is related to the environment, and since we were not able to replicate the issue and this is the only issue of this kind reported there is no way we could know more without investigating this deeper.
    Thanks!

Viewing 5 replies - 16 through 20 (of 20 total)
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