"Invisible" nodes

[roboticus]

G'morning all, I'm having a bit of trouble with perlmonks. This morning, I found that I get a blank page for a link, but if I changed the URL in the address bar from '.org' to '.com' I could access the page content.

I don't know if it's related to my being logged in or not, nor whether I'm getting a different server when I diddled the address. (I'm suspecting the former, though.)

Example: I started at this node, and when I clicked the link in the first reply, I get a blank page with http://www.perlmonks.org/?node_id=943568 in the address bar. On a whim, I changed the 'org' to 'com' and retried the link, and retried the link and got the expected page.

Browser:	Firefox 3.6.20 "Mozilla Firefox for Ubuntu canonical - 1.0"
uname -a	Linux Boink 2.6.32-33-generic #70-Ubuntu SMP Thu Jul 7 21:09:46 UTC 2011 i686 GNU/Linux

I'm going to stop until I get to work, and leave my browser sitting until I get home again. So if there's any information you'd like me to gather on my end, let me know. When I return from work, I'll go back and dig up the other node I saw that returns a blank page and try it, too.

Notes:

1. I've noticed nodes with empty content before, and it has been reproducible. This is, however, the first time I monkeyed with the address bar and got to the page.
2. I haven't cleared my browser cache or anything (just in case I can get some helpful data).

Update: I tried the example at work (on a different computer, OS, browser and network) and have similar results. Rather than a blank page, I get a "Network Error" page from our web filtering system.

Browser:	Firefox 7.0.1
OS:	Windows 7 Professional, 32-bit

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[choroba]

Probably the same as Is anyone at perlmonks aware that...?

[roboticus]

choroba:

I reviewed the thread, and I don't think it's the same error. I'll re-read the thread when I get home, and I'll check into it again. I'll bring this computer home and do a traceroute from both boxes to see what comes up.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[tye]

traceroute is likely of no use here. The variable of interest is which IP your browser is choosing to use at the time of the request for the hostname involved. As noted in that thread, more useful would be to look up the IPs associated with www.perlmonks.org and repeat the tests directly against the IPs and report which of them have and don't have the problem.

I believe that the two major problems covered in that thread are already fixed (and fixed a long time ago).

Fairly rarely I notice that certain nodes cause a Perl (inside mod_perl) core dump when viewed by certain people via certain web servers at certain times. When that happens, my browser gets a blank page in response. Sometimes I can make this symptom go away by restarting apache on that server. Sometimes the core dumps persist even after a restart but, again, only for certain nodes and only when viewed by certain people.

Switching from perlmonks.org to perlmonks.com might cause different behavior because at the time, your browser is choosing to use different IPs for those different host names (and not all of the servers are in a state where that problem happens). Or the change may be because you have a login cookie for one hostname but not for the other. The useful information is whether you are logged in or not and what IP the request went to. The host name is pretty much of no use at all, since I have no way of knowing what IP your browser was choosing to use for that hostname at that time.

When I run into the blank page problem and I can't be bothered to try restarting Apache (which is more work than I think it really should be), I can usually see the information I'm after by using a hostname that I don't have a login cookie for or by looking at the parent node in order to see the reply or by looking directly at the reply instead of at the parent.

This happens so rarely to me that I have not spent the likely great deal of time required to narrow down the problem further.

[tye]

Note that this problem appears to be fixed. See Broken link to "Cool Uses For Perl" for a more recent report of it where I originally replied about it having finally been fixed (I believe and hope, though it is somewhat difficult to verify conclusively).