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Status Update

Following on from the high level design, this page will provide a more detailed design approach to implement status update logging in the Java broker.

The logging hierarchy identified is not suitable to be directly used by Log4j as there is multiple routes and loops in the graph.

To better address this and to allow us to more eaily move between logging implementations an abstraction is recommended. This approach will allow the simplification of the logic around determining if logging should be performed in the main code base. For example a Binding logging statement can be controlled via Exchange and Queue, each of which may be limited to s specific instance.

This design will cover the following areas:

Logging Configuration

At this stage configuration will be limited to the addtion to the main config.xml file of the following option:

<broker>
 ...
 <logging>
    <level>INFO</level>
 <logging>
</broker>

This INFO level setting will be the default value if the section is not included in the configuration file. The setting will be global for all virtualhosts and will be exposed via the management console as logger 'qpid.operational' to allow dynamic level setting.

The ability to configure more fine grained logging will be investigated here, but will not be implemented in the initial phase.

Logging Levels

The following six levels represent the range of levels that will be available as part of the logging configuration. Whilst the initial implementation may not include specific messages at each level this section simply describes the type of message that would appear at each level and the behaviour associated with logging at that level. The levels are listed in order of the frequency of logging events. In addition to these six levels the values ALL and OFF may be used, these respectively represent TRACE and FATAL. FATAL messages will always be logged as they are associated with a broker shutdown.

FATAL
Occurs when an unrecoverable error has occured. A stack trace is automatically generated and a System.exit(1) is called halting the process.
e.g. Data corruption
ERROR
Occurs when a problem occurs in the system but it can generally continue to operate.
e.g. Unexpected error occurs that is limited to a single connection, i.e. not message store related.
WARN
Occurs when a potententialy harmful situation occurs.
e.g. Unexpected connection closure
INFO
General operational logging level, no logging on message delivery path way. No performance impact. Recommended for production use.
e.g. Creation/Destruction events
DEBUG
Additional logging on message delivery path way. May have performance impact. Not recommended for long term production use
e.g. Message Enqueue/Dequeue
TRACE
Full delivery path debugging. Will have performance impact. Not intended for production use.
e.g. Message selector behaviour

Logging Abstraction

The abstraction layer allows us to fully decouple the logging mechanism from any operational logging that the broker may wish to perform. The following code highlights show how we would abstract the logging operations.

OperationalLogger
public interface OperationalLogger
{
    public boolean isInfoEnabled(LogEntity entity);
    public void info(LogEntity entity, Object message);
    public void info(LogEntity entity , Object message, Throwable throwable);
// Repeated for each level TRACE|DEBUG|INFO|WARN|ERROR|FATAL
}
LogEntity
public interface LogEntity
{
    public String getLogPrefix();
    public void setCreator(LogEntity creator);
}

The LogEntity allows the OperationLogger to delegate the creation of the formated prefix as specfiecied here. Further additions to this interface may be required to enable selective configurations however this is not part of this design.

The addition of the ability to set a creator allows for situations such as Binding to have a Connection associated with the Binding. This will allow a Binding create event to be logged like this:

2009-06-29 13:35:10,1234 +0100 INFO [ con:1(guest@127.0.0.1/)/ch:2/ex(amq.direct)/qu(testQueue)/bd(routingKey) ] Created Binding

rather having no details about how the creation occured:

2009-06-29 13:35:10,1234 +0100 INFO [ vh(/)/ex(amq.direct)/qu(testQueue)/bd(routingKey) ] Created Binding

Logging Usage

Logging by a LogEntity
pubic class Subscription
...
    if (_statusLogger.isInfoEnabled(this))
    {
        _statusLogger.info(this, "Subscription Event occured.");
    }
...

Would result in the following based on the Logging Format Design.

2009-06-29 13:35:10,1234 +0100 INFO [ con:1(guest, 127.0.0.1, /)/ch:2/sub:1:qu(myqueue) ] Subscription Event occcured.
Logging of a newly created LogEntity via connection
...
    binding = new ExchangeBinding(...);
    ((LogEntity)binding).setCreator(connection);
... 
// Verify binding can be performed/created
...
    if (_statusLogger.isInfoEnabled(binding))
    {
        _statusLogger.info(binding, "Created");
    }
...

Would result in the following:

2009-06-29 13:35:10,1234 +0100 INFO [ con:1(guest, 127.0.0.1, /)/ch:2/pl(ACL, Consume, qu(myQueue)) ] Plugin Event occured for this. 

Initial Log Messages

FATAL

At this level it is only expected that broker/virtualhost wide components could cause a FATAL issue.

Broker
ManagementConsole
VirtualHost
MessageStore

MetaData not Found

ERROR

Broker

Startup errors

ManagementConsole

Startup errors
UserManagement notification(Create, Update, Delete)
Access Right modification/reload

VirtualHost
MessageStore

Recover errors

Connection

Unhandled exceptions leading to connection closure

Channel
Queue
Exchange
Binding
Subscription

WARN

Broker
ManagementConsole
VirtualHost
MessageStore
Connection

Unclean connection closure
Unsupported protocol version

Channel
Queue
Exchange
Binding
Subscription

INFO

Broker

Startup
Configuration details
Ready
Shutdown

ManagementConsole

Startup
Configuration details
Ready
Close

VirtualHost

Create
Configuration details
Close

MessageStore

Startup
Recover Status
Close

Connection

Open

Close

Channel

Create
Flow Status
Destroy

Queue

Create
Destroy

Exchange

Create
Destroy

Binding

Create
Destroy

Subscription

Create
Destroy

DEBUG

Broker
ManagementConsole
VirtualHost

Message Expiry

MessageStore
Connection

Creation Configuration details

Channel

Acknowledge
Commit
MessageRejection

Queue

Enqueue
Dequeue

Exchange

Route

Binding
Subscription

Send/Add to prefetch/unacked map

TRACE

Broker
ManagementConsole
VirtualHost
MessageStore

Enqueue
Dequeue

Connection
Channel
Queue

Message State Change(Available->Aquire...)

Exchange
Binding
Subscription
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