Top posting a solution -- I think I may have found a reason and a (temporary) solution. Actually, I didn't find it, but a helpful person at Stackoverflow suggested that I may be creating a $dbh that might be getting shared by different Starman preforked children (see link below). I think that was the case. I am still testing it by moving the $dbh creation in the subs. http://stackoverflow.com/questions/6721057/asynchronous-queries-with-mysql-p... So, instead of package mypackage; use Dancer ':syntax'; use DBI; my $dbh = DBI->connect(".."); get '/' => sub { template 'index'; }; get '/points.:format' => sub { my $bbox = params->{'BBOX'}; my $callback = params->{'callback'}; return $callback . '(' . to_json(points_within_bbox($bbox)) . ')'; }; get '/polys.:format' => sub { my $bbox = params->{'BBOX'}; my $callback = params->{'callback'}; return $callback . '(' . to_json(polys_within_bbox($bbox)) . ')'; }; sub points_within_bbox { my ($bbox) = @_; my $sth = $dbh->prepare(".."); $sth->execute($bbox); return $sth->fetchall_arrayref({}); } sub polys_within_bbox { my ($bbox) = @_; my $sth = $dbh->prepare(".."); $sth->execute($bbox); return $sth->fetchall_arrayref({}); } I now do the following package mypackage; use Dancer ':syntax'; use DBI; get '/' => sub { template 'index'; }; get '/points.:format' => sub { my $bbox = params->{'BBOX'}; my $callback = params->{'callback'}; return $callback . '(' . to_json(points_within_bbox($bbox)) . ')'; }; get '/polys.:format' => sub { my $bbox = params->{'BBOX'}; my $callback = params->{'callback'}; return $callback . '(' . to_json(polys_within_bbox($bbox)) . ')'; }; sub points_within_bbox { my ($bbox) = @_; my $dbh = DBI->connect(".."); my $sth = $dbh->prepare(".."); $sth->execute($bbox); return $sth->fetchall_arrayref({}); } sub polys_within_bbox { my ($bbox) = @_; my $dbh = DBI->connect(".."); my $sth = $dbh->prepare(".."); $sth->execute($bbox); return $sth->fetchall_arrayref({}); } It seems to be holding up. I am going to add another web service to the app, and see if it works. On Jul 16, 2011, at 8:05 PM, Mr. Puneet Kishor 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.