[Dancer-users] Follow-up: mysterious behavior putting Dancer app in production on Starman

[Mr. Puneet Kishor]

On Jul 14, 2011, at 8:55 PM, Mr. Puneet Kishor wrote:

> Check out the following [http://teststrata.geology.wisc.edu/macromap]. It should be working -- it should show a Google map backdrop with a bunch of polygons and a few points. As you pan and zoom, polys and points for the new viewport should be retrieved.
> 
> The polys and points are retrieved via ajax from [http://teststrata.geology.wisc.edu/mstrat/] that is serving them from a MySQL db as a REST service.
> 
> Both apps are Dancer based, and are running on Starman using the following invocation
> 
> $ plackup -p <port> -E production -s Starman -w 10 -a bin/app.pl
> 
> The first app (macromap) also has the -D switch added to the above plackup command so plackup runs in the background as a daemon (or a faceless app, or whatever is the correct terminology).
> 
> Here is the interesting thing -- if I add the -D switch to the second app as well, it fails to return the polys and the points. It fails with the error
> 
> {"error":"Warning caught during route execution: DBD::mysql::st fetchall_arrayref failed: fetch() without execute() at <path/to>/macrostrat.pm line 79.\n"}
> 
> The offending lines are
> 
> 	71> my $sql = qq{
> 	72> 	..
> 	73>
> 	74>
> 	75> };
> 	76> 
> 	77> my $sth = $dbh->prepare($sql);
> 	78> $sth->execute();
> 	79> my $res = $sth->fetchall_arrayref({});
> 
> The above could be just correlation rather than causal, but it definitely seems to be a pattern. First, this is bizarre, and why so? And, two... this is totally bogus... how can execute() not take place above? Perl doesn't have a habit of jumping over lines, does it?
> 
> Absolutely mystified in Madison.
> 


Following Paul Findlay's advice, I launched my offending app with the following invocation

	$DBI_TRACE=2=logs/dbi.log plackup -E production -p 5001 -s Starman -w 10 -a bin/app.pl

And, following is what stood out to me as the potential culprit in the log file

	> Handle is not in asynchronous mode error 2000 recorded: Handle is 
	> not in asynchronous mode
	>    !! ERROR: 2000 CLEARED by call to fetch method


(I am shooting in the dark here) I believe Dancer uses a lot of global variables. Would that be connected to this error? On occasion, I am also seeing another mysterious behavior, so mysterious that I feel I am smoking something --

One request to the web server pulls in points, and another request pulls in polys. They are called like so

	http://webserver/points.json
	http://webserver/polys.json

They are both separate asynchronous requests, sent via separate $.ajax() jQuery calls from the browser. On occasion, and I swear I am not making this up, I see points json stream returned via the polys request. Of course, because points.json returns different data than polys.json, I get an error.

For what its worth, and this is highly unscientific, this doesn't happen if plackup is in `-E development` mode. It only happens in the `-E production -D` mode. But, I could be wrong about this as I don't have a large enough sample set to confirm this finding conclusively.

Thoughts?