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  • Matt Wanchap 5 posts 85 karma points
    30 days ago
    Matt Wanchap

    Recurring "Xml cache is corrupt" issues

    After fresh deployments of our production site (during which ~\App_Data\ is deleted), sometimes the frontend part of the site refuses to load and Umbraco throws this exception: "The Xml cache is corrupt. Use the Health Check data integrity dashboard to fix it". It's a bit of a show-stopper and it keeps happening, so I'm trying to figure out some way to prevent it from occurring at the root cause.

    The Health Check Data Integrity dashboard always shows all green ticks, which makes sense since it says right on the dashboard "This does not check the data integrity of the xml cache file", which is apparently what's causing the exception.

    We're using TLS as we normally would and have umbracoUseSSL = true, so it's not due to that. We have a functioning workaround, which is to empty the recycle bin and then hit that "republish entire site" button, which always sorts things out, until the error randomly happens again a few weeks later (after many, many successful redeployments, I might add).

    I would really appreciate any input or insight that anyone might have into

    • Why the issue could happen in the first place
    • How we can detect it in advance or investigate the problem in some other direction, or catch / log / measure correlated things
    • Ideally, how to find the root cause, handle that situation and prevent the whole issue

    Some other thoughts:

    We're running Umbraco 7.15.0. The site runs in a single-instance Azure Web App and we're using a CI/CD blue/green style deployment from Azure Devops. This means the whole site is redeployed from scratch after a merge is made into the master branch. There are two deployment slots, we deploy into a staging slot, warm it up, and then swap with the production slot. We have quite a few content editors so inevitably deployments occur while they're in the middle of their work. Typically this is fine, but I wonder whether a lot of preview/publish work at the same time as a deployment slot swap could have something to do with this?

  • Nathan Woulfe 370 posts 1385 karma points MVP 2x c-trib
    29 days ago
    Nathan Woulfe

    Any plugins/packages running on the site?

    I've seen that error a few times in the last few days, after installing uSync, starting the site, running an export, then restarting the site. Uninstall uSync, remove all related files, and site restarts fine.

    I don't think uSync is the cause, but it's causing something else to flip out...

  • Matt Wanchap 5 posts 85 karma points
    29 days ago
    Matt Wanchap

    Hmm, interesting! We use usync too, but I'm a little hesitant to just remove it as usync is extremely handy for treating config changes as code. Not without a viable alternative, anyway.

    The weird thing is that most of the time there aren't any issues, and the recent deployments that have had this Xml cache corruption issue contained no usync changes, so I figure it wouldn't have been doing anything differently to the previously-successful deployments...

  • Steve Megson 98 posts 480 karma points c-trib
    28 days ago
    Steve Megson

    Is it specifically your editors seeing this error, or does it happen for other users too? There was an issue with preview in 7.15.0 (fixed in 7.15.1) which would throw this exception when it failed to generate the preview version of the XML cache.

    I think that emptying the recycle bin would clear that problem, since it was related to wrongly trying to generate preview data for deleted items.

  • Matt Wanchap 5 posts 85 karma points
    23 days ago
    Matt Wanchap

    Thanks for the tip about 7.15.1, hopefully this is the issue you mentioned and it's an easy fix! It just happened again, we hadn't even done a deployment but the site took ages to load so it had somehow restarted (which is weird in itself...)

    Looks like at the moment the issue is just affecting editors, and only when previewing (either via the backoffice, or accessing the site directly in preview mode). I actually remembered to grab a database export and a copy of /App_Data/ this time before fixing the problem, so hopefully I get a bit further with repro.

    And as before, emptying the recycle bin sorted things out immediately.

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