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[resolved] Intermittent White Screen from Mis-formed Cache (3 posts)

  1. skoskie
    Member
    Posted 5 months ago #

    Hi,

    Recently I've been intermittently getting the white screen. Upon investigation, I found that perfect good cache (.html) files that are not at all expired, are being replaced by incorrectly regenerated files.

    Here is an example of the regenerated html file:

    </body>
    </html>
    <!-- Dynamic page generated in 0.713 seconds. -->
    <!-- Cached page generated by WP-Super-Cache on 2014-02-06 17:43:53 -->
    
    <!-- super cache -->

    Note the timestamp. Here is the corresponding debug log with unrelated pages stripped out:

    ## A NORMAL REQUEST FOR THE PAGE IS HANDLED ##
    
    22:43:52 /2014/02/an-open-letter-to-all-racers/ supercache dir: /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/
    22:43:52 /2014/02/an-open-letter-to-all-racers/ Fetched static page data from supercache file using PHP. File: /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/index.html
    
    ## A NORMAL REQUEST FOR THE PAGE IS HANDLED ##
    
    22:43:52 /2014/02/an-open-letter-to-all-racers/ supercache dir: /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/
    22:43:52 /2014/02/an-open-letter-to-all-racers/ Fetched static page data from supercache file using PHP. File: /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/index.html
    
    ## A FEEDBURNER REQUEST FOR THE PAGE IS HANDLED, LEAVING THE INDEX.HTML FILE CORRUPT ##
    
    22:43:52 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 supercache dir: /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/
    
    22:43:52 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 No wp-cache file exists. Must generate a new one.
    22:43:52 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 In WP Cache Phase 2
    22:43:52 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Setting up WordPress actions
    22:43:52 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Created output buffer
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Output buffer callback
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Anonymous user detected. Only creating Supercache file.
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Writing non-gzipped buffer to supercache file.
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Renamed temp supercache file to /nfs/c07/h01/mnt/123/domains/fitbottomedgirls.com/html/wp-content/cache/supercache/fitbottomedgirls.com/2014/02/an-open-letter-to-all-racers/index.html
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Sending buffer to browser
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 wp_cache_shutdown_callback: collecting meta data.
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Sending 'Content-Type: text/html; charset="UTF-8"' header.
    22:43:53 /2014/02/an-open-letter-to-all-racers/?utm_source=feedburner&utm_medium=twitter&utm_campaign=Feed%3A+FitBottomedGirls+%28Fit+Bottomed+Girls%29 Did not write meta file: wp-cache-a4b819c5a662f55209f5c233f6acf2e4.meta *1* *0* *1*

    At this point the file is now useless. I have to manually clear the cache for this page.

    If I clear the cache for this page (or the entire site) and try to trigger the error again by pasting the above URL in by browser, it re-creates the cache file and renders just fine.

    My settings (seen here: http://cl.ly/Tn5B) have always been set to NOT cache urls with query strings. However, it isn't limited to URLs with query strings. It's getting caught up on images and other files too. I have a directory in my supercache folder called apple-touch-icon.png with another mis-generated html file like the one above.

    This is a rather large site, so we are a little slower and more cautious about upgrading. We haven't upgraded any plugins or WP itself since well before the issue started. The only recent update we made, was manually adding some security settings to the .htaccess file to filter certain query strings. I've since reverted those changes just to ensure they are not the cause of our issues.

    Any ideas on what could be causing this to happen?

    https://wordpress.org/plugins/wp-super-cache/

  2. Donncha O Caoimh
    Member
    Plugin Author

    Posted 5 months ago #

    It looks like some other plugin is corrupting the output buffer. As it's intermittent it'll be hard to figure out which one.

    It could also be a memory or CPU load issue. I've seen weird things happen when memory gets tight.

    You could edit wp-cache-phase2.php and look for wp_cache_ob_callback. If the $buffer passed to that is

    </body>
    </html>

    then you should use error_log() to try and log as much information as possible about the cause. That may help figure out why this is happening.

  3. skoskie
    Member
    Posted 4 months ago #

    For what it's worth, I found the issue to be incompatibility with a compression setting in the .htaccess file. All compression of the text/html content type had to be removed, which resolved the issue immediately.

    So, remove the bottom line in this block....

    <IfModule filter_module>
        FilterDeclare   COMPRESS
        FilterProvider  COMPRESS  DEFLATE resp=Content-Type $text/html

    ... and in this block, remove the text/html content type...

    <IfModule !mod_filter.c>
        # Legacy versions of Apache
        AddOutputFilterByType DEFLATE text/html text/plain text/css application/json

    I hope this helps someone in the future.

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