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RSS feed not getting GC'd (6 posts)

  1. amattie
    Member
    Posted 1 year ago #

    We recently upgraded from an old version of WP Super Cache (0.9 I believe) to 1.2, and we're now having problems with our RSS feed being stale. I did some digging, and it looks to me like the garbage collector isn't cleaning up the feed perhaps due to a bug. Here's the relevant debug log:

    // hit feed for the first time w/ an empty cache dir
    15:43:19 /blog/feed/ supercache dir: [...]wp-content/cache/supercache/www.example.com/blog/feed/
    15:43:19 /blog/feed/ No wp-cache file exists. Must generate a new one.
    15:43:20 /blog/feed/ In WP Cache Phase 2
    15:43:20 /blog/feed/ Setting up WordPress actions
    15:43:20 /blog/feed/ Created output buffer
    15:43:23 /blog/feed/ Output buffer callback
    15:43:23 /blog/feed/ Feed detected. Writing legacy cache files.
    15:43:23 /blog/feed/ Supercache disabled: GET or feed detected or disabled by config.
    15:43:23 /blog/feed/ Writing non-gzipped buffer to wp-cache cache file.
    15:43:23 /blog/feed/ Renamed temp wp-cache file to [...]wp-content/cache/blogs/feed/wp-cache-feed0671fa3f67fb255e6141869e80660f1f.html
    15:43:23 /blog/feed/ Sending buffer to browser
    15:43:23 /blog/feed/ wp_cache_shutdown_callback: collecting meta data.
    15:43:23 /blog/feed/ Writing meta file: [...]wp-content/cache/blogs/feed/meta/wp-cache-feed0671fa3f67fb255e6141869e80660f1f.meta

    // hit feed after it's been primed in the cache
    15:44:09 /blog/feed/ wp-cache file exists: [...]wp-content\cache\blogs\feed\wp-cache-feed0671fa3f67fb255e6141869e80660f1f.html
    15:44:09 /blog/feed/ Serving wp-cache static file
    15:44:09 /blog/feed/ exit request

    // hit wp-cron when a GC is scheduled
    16:01:46 /blog/wp-cron.php In WP Cache Phase 2
    16:01:46 /blog/wp-cron.php Setting up WordPress actions
    16:01:46 /blog/wp-cron.php URI rejected. Not Caching
    16:01:46 /blog/wp-cron.php maybe_stop_gc: GC flag not found. GC will go ahead..
    16:01:46 /blog/wp-cron.php wp_cache_gc_cron: Set GC Flag. ([...]wp-content/cache/www.example.com/blog_wp_cache_gc.txt)
    16:01:46 /blog/wp-cron.php Cache garbage collection.
    16:01:46 /blog/wp-cron.php Cleaning expired cache files in [...]wp-content/cache/
    16:01:46 /blog/wp-cron.php Doing GC on supercache dir: [...]wp-content/cache/supercache
    16:01:46 /blog/wp-cron.php gc: deleted [...]wp-content/cache/supercache/www.example.com/blog/feed, older than 600 seconds
    16:01:46 /blog/wp-cron.php gc: could not delete [...]wp-content/cache/supercache/www.example.com as it's not empty: blog
    16:01:46 /blog/wp-cron.php GC completed. GC flag deleted.
    16:01:46 /blog/wp-cron.php scheduled wp_cache_gc for 10 seconds time.

    // hit the feed again just to show the cached file is still being served
    16:22:55 /blog/feed/ wp-cache file exists: [...]wp-content\cache\blogs\feed\wp-cache-feed0671fa3f67fb255e6141869e80660f1f.html
    16:22:55 /blog/feed/ Serving wp-cache static file
    16:22:55 /blog/feed/ exit request

    As you see, when the feed is requested, WP Super Cache generates the static cache file and then stores it in the wp-content\cache\blogs\feed\ dir. Later, when the GC uses wp_cache_phase2_clean_expired to clean up the expired files, the "while ... readdir" loop only looks at the files in that directory alone instead of recursing through all directories and files. The feed ultimately isn't GC'd then because it's in the blogs/feed/ folder instead of the top-level directory.

    Can someone confirm that this is actually a bug and not somehow a misconfiguration?

    http://wordpress.org/extend/plugins/wp-super-cache/

  2. _ck_
    Member
    Posted 1 year ago #

    Unless donncha has addressed it in newer versions, feeds aren't cached (any longer?) as static files because of the header difference for feeds.

    But I sure would like to fix that and make feeds static too.

  3. Donncha O Caoimh
    Member
    Plugin Author

    Posted 1 year ago #

    @amattie - is your blog installed in /blog/ ? The feed should be stored in ../cache/blogs/HOSTNAME/, and not in cache/blogs/feed/

    @_ck_ - they're cached, but using legacy caching so those headers can be sent :)

  4. _ck_
    Member
    Posted 1 year ago #

    "legacy caching" means php loads to send the headers and then dumps the static file?

    there has to be a way to avoid that - I'll study it this weekend, not sure why feeds would need any kind of special headers for logged out users

  5. amattie
    Member
    Posted 1 year ago #

    Yeah, our primary blog is installed in /blog/. Other blogs in our MU setup are on that same path prefix (/blog/blog2, /blog/blog3, etc). It appears that only the primary blog has feed caching broken for us.

    Is this setup not currently supported? It seems to be a problem with $blogcacheid assigned in wp-cache-base.php -- the value gets set to "feed/" on line 27 since the blog name isn't in the primary blog's URL.

  6. Jeremy Clarke
    Member
    Posted 11 months ago #

    Still a problem! I'm having exactly the same issue and it's starting to drive me crazy. It's a pretty serious issue because it's easy to not notice a stale RSS feed. It is likely affecting many more people than have noticed.

    Like amattie I have multisite running and the main site is set up as /blog/, my other sites are not /blog/$x/ though, they are root directories on the domain (domain.com/site2/).

    Like amattie I can see the cache file for the main feed in /wp-content/cache/blogs/feed/***

    If I push the "Delete cache" button on the main site it does not clear the cache for this RSS feed, however if I click the "Delete cache on all blogs" button in the "Contents" tab of Supercache it does refresh the RSS feed.

    I believe the core issue is that Supercache is treating /feed/ on sites with subdirectory-configs as a separate site and caching based on that assessment. We're noticing it because the "/feed/" subsite doesn't exist, so the garbage collection for it never runs.

    I think the fix will involve ensuring that /feed/ urls are correctly associated with the main site and their garbage collected during that site's run.

    Thanks for any help you can provide Donncha, I'm sure overall this is a rare and hard-to-reproduce bug. I had a hell of a time just finding this thread :)

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