X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?p=scpubgit%2FObject-Remote.git;a=blobdiff_plain;f=lib%2FObject%2FRemote.pm;h=2c8c096ff2ccd8a343f5a4be83e398f4e6e95583;hp=f937fb37f05dfc812a247156aaa72171bd20192b;hb=b0ec7e3b19d47b9ba5a864f5077d0dc8030834cc;hpb=f21d2f9042fbad3e958979f4db37f051b3c50998

diff --git a/lib/Object/Remote.pm b/lib/Object/Remote.pm
index f937fb3..2c8c096 100644
--- a/lib/Object/Remote.pm
+++ b/lib/Object/Remote.pm
@@ -150,8 +150,8 @@ L<Object::Remote::Logging::Logger>.
 
 =item OBJECT_REMOTE_LOG_FORWARDING
 
-Forward log events from remote connections to the local Perl interpreter. Set to 0 to disable
-this feature which is enabled by default. See L<Object::Remote::Logging>.
+Forward log events from remote connections to the local Perl interpreter. Set to 1 to enable
+this feature which is disabled by default. See L<Object::Remote::Logging>.
 
 =item OBJECT_REMOTE_LOG_SELECTIONS
 
@@ -161,6 +161,69 @@ See L<Object::Remote::Logging::Router>.
 
 =back
 
+=head1 KNOWN ISSUES
+
+=over 4 
+
+=item Large data structures
+
+Object::Remote communication is encapsalated with JSON and values passed to remote objects
+will be serialized with it. When sending large data structures or data structures with a lot
+of deep complexity (hashes in arrays in hashes in arrays) the processor time and memory requirements
+for serialization and deserialization can be either painful or unworkable. During times of
+serialization the local or remote nodes will be blocked potentially causing all remote
+interpreters to block as well under worse case conditions.
+
+To help deal with this issue it is possible to configure the ulimits for a Perl interpreter
+that is executed by Object::Remote. See C<Object::Remote::Connection> for details.
+
+=item User can starve run loop of execution opportunities
+
+The Object::Remote run loop is responsible for performing I/O and managing timers in a cooperative
+multitasing way but it can only do these tasks when the user has given control to Object::Remote.
+There are times when Object::Remote must wait for the user to return control to the run loop and
+during these times no I/O can be performed and no timers can be executed.
+
+As an end user of Object::Remote if you depend on connection timeouts, the watch dog or timely
+results from remote objects then be sure to hand control back to Object::Remote as soon as you
+can.
+
+=item Run loop favors certain filehandles/connections
+
+=item High levels of load can starve timers of execution opportunities
+
+These are issues that only become a problem at large scales. The end result of these two
+issues is quite similiar: some remote objects may block while the local run loop is either busy
+servicing a different connection or is not executing because control has not yet been returned to
+it. For the same reasons timers may not get an opportunity to execute in a timely way.
+
+Internally Object::Remote uses timers managed by the run loop for control tasks. Under
+high load the timers can be preempted by servicing I/O on the filehandles and execution
+can be severely delayed. This can lead to connection watchdogs not being updated or connection
+timeouts taking longer than configured.
+
+=item Deadlocks
+
+Deadlocks can happen quite easily because of flaws in programs that use Object::Remote or 
+Object::Remote itself so the C<Object::Remote::WatchDog> is available. When used the run
+loop will periodically update the watch dog object on the remote Perl interpreter. If the
+watch dog goes longer than the configured interval with out being updated then it will
+terminate the Perl process. The watch dog will terminate the process even if a deadlock
+condition has occured.
+
+=item Log forwarding at scale can starve timers of execution opportunities
+
+Currently log forwarding can be problematic at large scales. When there is a large
+amount of log events the load produced by log forwarding can be high enough that it starves
+the timers and the remote object watch dogs (if in use) don't get updated in timely way
+causing them to erroneously terminate the Perl process. If the watch dog is not in use
+then connection timeouts can be delayed but will execute when load settles down enough.
+
+Because of the load related issues Object::Remote disables log forwarding by default.
+See C<Object::Remote::Logging> for information on log forwarding.
+
+=back
+
 =head1 SUPPORT
 
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