[Dancer-users] Follow-up: mysterious behavior putting Dancer app in production on Starman
Mr. Puneet Kishor
punk.kish at gmail.com
Sun Jul 17 16:58:39 CEST 2011
Knock knock? Anyone, any ideas? I realize not much time has passed since I posted this, but I have until tomorrow to get a concept demo ready. So, I have to decide today whether or not to continue on this path or cut bait.
On Jul 16, 2011, at 8:05 PM, Mr. Puneet Kishor <punk.kish at gmail.com> wrote:
> Following with more investigation and observation (please see below) --
>
> On Jul 15, 2011, at 9:07 AM, Mr. Puneet Kishor wrote:
>
>>
>> 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?
>>
>
> A simple script like so works like a champ... no async nonsense, no errors. All 1000 requests are effortlessly returned by the same set up.
>
> use LWP::UserAgent;
>
> my $BBOX = "-96.09299316406248+38.96034339396338%2C+83.39279785156248+38.96034339396338%2C+-83.39279785156248+44.33256692562997%2C+96.09299316406248+44.33256692562997%2C+-96.09299316406248+38.96034339396338";
>
> for (1 .. 1000) {
> open my $fh, ">>", 'foo.txt';
>
> my $ua = LWP::UserAgent->new;
> $ua->agent("MyApp/0.1 ");
>
> my $req = HTTP::Request->new(GET => "http://localhost:5001/points.json?callback=foo&BBOX=$BBOX");
> my $res = $ua->request($req);
>
> # Check the outcome of the response
> if ($res->is_success) {
> say $fh $res->content;
> }
> else {
> say $fh $res->status_line;
> }
>
> close $fh;
> }
>
> So, it seems that both MySQL and Starman are very capable of handling this. The only element missing here is Dancer, and the browser. Thoughts anyone? I am just interested in finding out the issues here, and creating a robust, workable app.
>
> Many thanks in advance.
>
> Puneet.
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