Re: Using DBI

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Octavian Rasnita wrote:
> Hi all,
> 
> I am a new member on this list and after reading the posts from this list in
> the last few days, I don't even know if this is the apropriate place for
> asking questions about using mod_perl.
> If it is not, please tell me if there is another list which could be more
> useful for a mod_perl beginner.
> 
> I want to use the DBI module with mod_perl 2 with Perl 5.8.4, and for the
> moment... under Windows 2000.
> 
> I have tried:
> 
> In httpd.conf:
> PerlRequire [path]/preload.pl
> 
> in preload.pl:
> use Apache::DBI();
> use DBI ();
> DBI->install_driver("mysql");
> ###Apache::DBI->connect_on_init("DBI:mysql:database=presa;host=localhost",
> "ODBC", undef, {PrintError =>1, RaiseError=>0, AutoCommit => 1});
> 
> in the GetCategories.pm module:
> ##use Apache::DBI;
> use DBI;
> my $dbh = ...;
> 
> I have tried more combinations, but every time I get the following error in
> the logs:
> 
> [Tue Dec 28 21:07:34 2004] [error] DBD::mysql::db prepare failed: handle 2
> is owned by thread 265c564 not current thread 14ce78c (handles can't be
> shared between threads and your driver may need a CLONE method added) at
> f:/web/presa/modules/GetCategories.pm line 18.\n
> -----
> 
> So I have commented out the following line in preload.pl:
> ###Apache::DBI->connect_on_init("DBI:mysql:database=presa;host=localhost",
> "ODBC", undef, {PrintError =>1, RaiseError=>0, AutoCommit => 1});
> 
> And in GetCategories.pm I have used only:
> 
> use DBI;
> my $dbh = ...;
> 
> Well, in this case the script works, but I don't know if this way of using
> DBI is the best way.

I'm afraid your script, just appears to be working and if you put it under 
a  stress testing, that will really involve multithreading you will see 
the same problem. Take a look at:
http://search.cpan.org/~rudy/DBD-mysql-2.9004/lib/DBD/mysql.pm#MULTITHREADING

-----------------------------
The multithreading capabilities of DBD::mysql depend completely on the 
underlying C libraries: The modules are working with handle data only, no 
global variables are accessed or (to the best of my knowledge) thread 
unsafe functions are called. Thus DBD::mysql is believed to be completely 
thread safe, if the C libraries are thread safe and you don't share 
handles among threads.

The obvious question is: Are the C libraries thread safe? In the case of 
MySQL the answer is "mostly" and, in theory, you should be able to get a 
"yes", if the C library is compiled for being thread safe (By default it 
isn't.) by passing the option -with-thread-safe-client to configure. See 
the section on How to make a threadsafe client in the manual.
-----------------------------

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