Re: DBI Mysql Driver Handle Mysteriously Changes!

On Thu, Mar 27, 2014 at 04:43:41PM +1300, Duncan McEwan wrote:
> 
> > > I've got 1000's of lines of debugging showing this happening.  Some of it
> > > is my own, inserted as print statements or cluck calls directly into DBI.pm
> > > and some of it the standard DBI debugging set to level 9.  There is way too
> > > much to include in this message, but I've included some small extracts below
> > > to illustrate what I am seeing.
> > 
> > What you've included doesn't show the drh changing.
> 
> Then maybe I'm mis-interpreting the debugging I'm seeing?

No, nevermind, I was. Thanks.

> > I suggest you focus on that. Specifically the code path taken by the
> > request that notices that the drh has changed, _and_ the code path taken
> > by the _previous_ request _in the same process_.
> 
> Yes.  I had been looking at that.  Within DBI.pm I've inserted calls to
> cluck so I could see the stack trace both the case when a cached database
> handle is returned and when a new one is created.  There were *sometimes*
> differences in the call stack between those times, but sometimes not.
> 
> At the moment I only turn DBI tracing on in the connect_cached() call and
> turn it off again before the call returns.  I did that because I was worried
> about the amount of output that would be produced if I left tracing on.
> But perhaps that is what I will have to do.

Perhaps you don't need to output it. Call $stacktrace = Carp::longmess
and only output it if the stacktrace is different to the last one, or
some similar logic.

Also try turning on $drh->{TraceLevel} after the $dbh is created.
That'll then log just future connect_cached calls *and* handle
destruction, which might be useful.

> A potential further complication that I didn't mention previously is that
> our application (which I *did* mention is written as a foswiki plugin)
> uses the CGI::Application perl package.  From a very quick look at its
> code, it does seem to know about the DBI and could perhaps be doing something
> "too clever" which is causing us problems.  I'll look more into that as
> well.

I didn't see anything suspicious in CGI::Application
https://metacpan.org/source/MARKSTOS/CGI-Application-4.50/lib/CGI/Application.pm
or CGI::Application::Plugin::DBH
https://metacpan.org/source/FREW/CGI-Application-Plugin-DBH-4.04/lib/CGI/Application/Plugin/DBH.pm

For more areas to dig, note the mention of dbi_connect_method
in https://metacpan.org/pod/DBI#connect and
https://metacpan.org/source/TIMB/DBI-1.631/DBI.pm#L571

Keep focused on why a new drh appears.

See https://metacpan.org/source/TIMB/DBI-1.631/DBI.pm#L652
Perhaps something is altering %DBI::installed_drh

Tim.