new branch grouped_has_many_join

[dbsrgits/DBIx-Class.git] / lib / DBIx / Class / Manual / Troubleshooting.pod

diff --git a/lib/DBIx/Class/Manual/Troubleshooting.pod b/lib/DBIx/Class/Manual/Troubleshooting.pod
index c9aa40b..e3b1ab3 100644 (file)
--- a/lib/DBIx/Class/Manual/Troubleshooting.pod
+++ b/lib/DBIx/Class/Manual/Troubleshooting.pod
@@ -17,11 +17,11 @@ SQL tracing, so to see what is happening try
 
 Alternatively use the C<< storage->debug >> class method:-
 
-  $class->storage->debug(1);
+  $schema->storage->debug(1);
 
 To send the output somewhere else set debugfh:-
 
-  $class->storage->debugfh(IO::File->new('/tmp/trace.out', 'w');
+  $schema->storage->debugfh(IO::File->new('/tmp/trace.out', 'w');
 
 Alternatively you can do this with the environment variable too:-
 
@@ -47,7 +47,7 @@ correctly.
 
 L<DBI> version 1.50 and L<DBD::Pg> 1.43 are known to work.
 
-=head2 ... Can't locate object method "source_name" via package ...
+=head2 Can't locate object method "source_name" via package
 
 There's likely a syntax error in the table class referred to elsewhere
 in this error message.  In particular make sure that the package
@@ -123,5 +123,38 @@ Now you'll get SQL like this:
 
   ... ORDER BY name DESC
 
+=head2 Perl Performance Issues on Red Hat Systems
+
+There is a problem with slow performance of certain DBIx::Class
+operations using the system perl on some Fedora and Red Hat Enterprise
+Linux system (as well as their derivative distributions such as Centos,
+White Box and Scientific Linux).
+
+Distributions affected include Fedora 5 through to Fedora 8 and RHEL5
+upto and including RHEL5 Update 2. Fedora 9 (which uses perl 5.10) has
+never been affected - this is purely a perl 5.8.8 issue.
+
+As of September 2008 the following packages are known to be fixed and so
+free of this performance issue (this means all Fedora and RHEL5 systems
+with full current updates will not be subject to this problem):-
+
+  Fedora 8     - perl-5.8.8-41.fc8
+  RHEL5        - perl-5.8.8-15.el5_2.1
+
+The issue is due to perl doing an exhaustive search of blessed objects
+under certain circumstances.  The problem shows up as performance
+degredation exponential to the number of L<DBIx::Class> row objects in
+memory, so can be unoticeable with certain data sets, but with huge
+performance impacts on other datasets.
+
+A pair of tests for susceptability to the issue, and performance effects
+of the bless/overload problem can be found in the L<DBIx::Class> test
+suite in the file C<t/99rh_perl_perf_bug.t>
+
+Further information on this issue can be found in
+L<https://bugzilla.redhat.com/show_bug.cgi?id=379791>,
+L<https://bugzilla.redhat.com/show_bug.cgi?id=460308> and
+L<http://rhn.redhat.com/errata/RHBA-2008-0876.html>
+
 =cut