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Forums: Index > Help desk > Backtrace limit exceeded during parsing!


Here's an error message that's new to me. Appeared at the top of the screen, repeated, after I entered a short name in the "create person page" form:

Semantic Forms error: backtrace limit exceeded during parsing! Please increase the value of pcre.backtrack-limit in the PHP settings.

Do we have a new problem?

-- Robin Patterson (Talk) 08:44, December 26, 2012 (UTC)

It's still happening. It may indicate that we are losing more functionality than usual. I checked the indicated link; a discussion there suggested that the limit can be raised enormously without detriment. But I've no idea who can change PHP settings. Any ideas, or do we Contact Wikia? -- Robin Patterson (Talk) 03:09, January 9, 2013 (UTC)

I think that is definitely in the Wikia admin department. Thurstan (talk) 03:16, January 9, 2013 (UTC)

It's in the php.ini file in the public-html directory, that's the directory that contains the wiki (public_html/wiki). But a familypedia administrator would have to have ftp access to change it (Edit with a plain text editor). The code to change there is:

[Pcre]
;PCRE library backtracking limit.
;pcre.backtrack_limit=100000

I don't know what the new limit should be. Whroll (talk) 15:19, March 11, 2013 (UTC) :)

Here's the full error message taken from html page source:

Semantic Forms error: backtrace limit exceeded during parsing! Please increase the value of <a href="http://www.php.net/manual/en/pcre.configuration.php#ini.pcre.backtrack-limit">pcre.backtrack-limit</a> in the PHP settings.Semantic Forms error: backtrace limit exceeded during parsing! Please increase the value of <a href="http://www.php.net/manual/en/pcre.configuration.php#ini.pcre.backtrack-limit">pcre.backtrack-limit</a> in the PHP settings.

The link offers some suggestions about the what the new setting should be. http://www.php.net/manual/en/pcre.configuration.php#ini.pcre.backtrack-limit Whroll (talk) 15:44, March 11, 2013 (UTC)

The directory familypedia that you see in the url is an alias. The name of the directory on the wikia server is public_html. The root directory for "familypedia" should be one level above public_html. Whroll (talk) 16:24, March 11, 2013 (UTC)

I don't believe that anyone but central Wikia operators get FTP access. Thurstan (talk) 19:37, March 11, 2013 (UTC)
OK, chaps, one of you could use "Contact Wikia", referring to this page. You clearly know more about the technicalities than I do, and I've already bothered staff with a "Contact" complaint in the last 24 hours! -- Robin Patterson (Talk) 01:23, March 12, 2013 (UTC)
Not me: we just lose our "custom settings" every upgrade. That is what happened last July. Thurstan (talk) 03:31, March 12, 2013 (UTC)

I don't know a great deal about wikis, just some things I have learned while fiddling with my own Wikimedia site at Bluehost. I don't know the differences between Wikia's wikis and normal Wikipedia installations yet. In the next couple of days I will start a temporary wiki on Wikia and examine the access that an administrator has here. I always hesitate to ask for help, because it has proven much easier to just search with Google for the needed information myself! A persistent error message is not good for publicity even is it is benign. Whroll (talk) 14:34, March 22, 2013 (UTC)

Well...I set up a wikia wiki. It looks like bureaucrats and administrators here have precious little access to the inner workings of their own wiki. Where do I contact someone who has the ability to make this measly change in php.ini? By the way PHP is a script that throws together various elements, on the fly, into viewable web pages as you request them. Whroll (talk) 20:41, March 22, 2013 (UTC)

"Contact Wikia" (suggested above) is a simple form-based procedure, which can be accessed in a number of ways, the most obvious probably being the link in the middle of the blue links at the bottom of many pages. (I have one on "My Tools" in my bottom toolbar.) "Be bold". You should refer them to this forum. I agree that error messages are best cut out if we don't have to repeat the cure every few days. -- Robin Patterson (Talk) 00:23, March 23, 2013 (UTC)

I put it to the experts[]

Here's my set of questions and the replies from Yaron, one of the designers of SF:


Hi Robin,


Let me just note that trying to isolate the issue, or issues, in the form shouldn't take thousands of hours, at least assuming that that "backtrace limit" error message is at least somewhat reproducible. What I would suggest is to create a copy of the form, to be used as your test form, then eliminate and re-add parts of it, checking for that message each time, to try to get a sense for which section(s) of the form are the likely culprit. If you can get the error to consistently display, at least on certain pages, with the current form, the whole process might not take more than an hour or two. If you can't, though, it's probably a different story.


-Yaron


On Sun, Sep 27, 2015 at 9:52 PM, Robin Patterson <Robin-P@slingshot.co.nz> wrote:

It's great to get a reply from a real expert. Thank you, Yaron.

However, your reply doesn't take us far.

  1. 1: There are so many unsatisfactory aspects of our use of the form and the resulting displays that we ordinary amateur genealogists have no way of telling whether the backtrace limit "problem" is causing any of them. Even Wikia's best brains can't explain why we don't get all the results we should.
  1. 2 The form is indeed complex; that's because people are, and we want to display an individual's page with as much detail as possible. Showing the date and place (street address, locality+county+state+nation, for example) of someone's tenth marriage isn't necessary for most people but is for a few, and the form tries to cover that and hundreds of similar properties.. And its complexity is a reason why we would not want to spend thousands of hours simplifying one part after another to see whether it might reduce the number of backtrace "errors" - especially if they aren't actually problems. If you, an SF expert, can only guess, what hope is there for us?
  1. 3 We can't approach the host asking for an increase in the limit unless we have some idea what that might do to the functioning of the wiki.

I've googled "set backtrace limit". Some of the more informative-looking hits in the top ten may help programmers but are of little or no help to amateur genealogists (nor, probably, to ordinary users of other SF sites where the same error message could appear). Some - such as http://www.slac.stanford.edu/comp/unix/package/rtems/doc/html/gdb/gdb.info.Backtrace.html - predate SF. But the error message says "Semantic Forms error". That text must surely have been created by someone who knew how the error could relate to a semantic form. If we could get hold of that person we might get further in deciding whether to continue ignoring the error message. Even talking to someone else who has experienced that error message might help. I hope some such person is reading this and will come forward.

Robin F Patterson, 88 Motuhara Road, Plimmerton, Porirua 5026, NZ

http://familypedia.wikia.com/wiki/User:Robin_Patterson


Original Message -----

From: Yaron Koren To: Robin Patterson Cc: Users, Semantic MediaWiki Sent: Monday, September 28, 2015 10:37 AM Subject: Re: [Semediawiki-user] [SF] backtrace limit


Hi Robin,


I would think you'd be the best person to judge #1, since you (or the wiki's users) would see any issues that come up. If you haven't seen any, then it might fine.


The form looks a little complex! It calls all sorts of templates and parser functions. I'm guessing that simplifying it would get rid of the error message. It could well be that just one of those calls is responsible for hitting the backtrace limit.


As for actually increasing the limit, that's up to the Wikia people.


-Yaron


On Fri, Sep 25, 2015 at 11:48 PM, Robin Patterson <Robin-P@slingshot.co.nz> wrote:

On Familypedia (wiki-of-the-month some years ago) we often see this when starting a new page with Form:Person:

Semantic Forms error: backtrace limit exceeded during parsing! Please increase the value of pcre.backtrack_limit in php.ini or LocalSettings.php.

Whatever it is, it seems not to spoil our page-creation process. Three questions:

1. Is the exceeding of the limit likely to affect anything an ordinary user does?

2. If we should attend to it, is it the sort of thing an admin can do or will it require a request for host (Wikia, Inc) staff to fix?

3. What determines the extent to which we should ideally increase the limit?

Robin F Patterson, 88 Motuhara Road, Plimmerton, Porirua 5026, NZ

http://familypedia.wikia.com/wiki/User:Robin_Patterson


-- Robin Patterson (Talk) 14:57, September 28, 2015 (UTC)

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