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Logging Control

Initialy the use of a properties file will be used to enable/disable various logging options. The property value will be one of a set list. This will help avoid the ambigious parsing of Java Properties files.

# Comment Line
<logger> = <value [OFF|TRACE|DEBUG|INFO|WARN|ERROR|FATAL|ALL]>

The values for the <logger> are based on navigation through the hierarchy.

Hierarchy Refinement

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qpid ─┬─ broker
      │
      │
      │              ┌── [<username>] ───┐
      │              ├─ [<ip/hostname>] ─┤
      ├─ connection ─┴───── [<id>] ──────┴─ channel ── [<id>] ──────┬── subscription ── [<id>]
      │                                                             │
      └─ virtualHost ── <name> ─┐                      ┌─  binding  │
                                │                      │            │
                                ├─ exchange ── <name> ─┤            │
                                │                      │            │
                                ├─ queue ── <name> ────┴────────────┘         
                                │                             
                                ├─ plugin ── <name>
                                │                 
                                └─ messagestore 

At this state the configurability of logging will be limited to selection of logging level. Further details on the approach to provide configurable logging can be found here.

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

This hierachy has a number of paths which make it more difficult to process.

1. Connection can be optionally followed with up to one of the following: username,ip/host, id
2. Subscription can be reached through Connection and Virtualhost
3. Exchange and Queue can be added in either order
4. Binding can be routed through Queue and Exchange, or both in either order.

It is these difficulties that make it best to provide an abstraction layer so that a simple interface can be used at the site of the logging. These difficulties can be distilled to:

1. Procsessing values for all values of '<name>'
2. Overlapping configuration resolution
3. Presentation of entities with multiple paths

Procsessing values for all values of '<name>'

To ensure that the logger path is processable the '<name>' must be present to make it easier to understand when we have an identifier or a <name> value. i.e. Is this logging all events for exchanges on Virtualhost called 'queue' or logging all exchange events that occur in relatation to queues.

qpid.virtualhost.queue.exchange = INFO

By introducing the use of the '*' wild card we can make these two situations easier to read:

qpid.virtualhost.queue.exchange = INFO
qpid.virtualhost.*.queue.exchange = INFO

The '*' can then be used at the end of the logger to ensure all logging from this point in the hierarchy will be logged, rather than just events to the specified entity.

Overlapping configuration resolution

The loops in the graph will be handled by the logger configurator so that only one log entry is created for each event, even if there are multiple matching entries in the configuration. For example, the follow two entries are equivalent and will both enable all loging for bindings. If the user wishes to log all binding operations then only one entry is necessary but the presence of both should not cause duplicate messages.

qpid.virtualhost.*.exchange.*.binding = INFO
qpid.virtualhost.*.queue.*.binding = INFO

The overlapping of configuration such as logging all details of connection from user guest and from ip 127.0.0.1 will not result in a duplicated logging if guest connects from 127.0.0.1.

qpid.connection.guest.* = INFO
qpid.connection.<127.0.0.1>.* = INFO

Presentation of entities with multiple paths

Each entitiy will have a prescribed log format which will be designed to take into consideration its place in the hierarchy, see Logging Format Design for further details.

Log Configuration processing

The configuration will be processed top-to-bottom. This allows for defaults to be set and specific cases to have further logging enabled. The example below enables INFO logging for all events and specifically adds DEBUG logging for all activity related to the user 'guest'.

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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.

public interface OperationalLogger
{

    public boolean isInfoEnabledForPluginisInfoEnabled(Plugin p, Object oLogEntity entity);
    public void pluginInfoinfo(PluginLogEntity pentity, Object omessage);
    public void pluginInfoinfo(PluginLogEntity entity p, Object omessage, Throwable throwable);
// Repeated for each level 
    public boolean isInfoEnabled(Object o);TRACE|DEBUG|INFO|WARN|ERROR|FATAL
}

public interface LogEntity
{
    public voidString infogetLogPrefix(Object o);
    public void infosetCreator(Object o, Throwable throwableLogEntity creator);
...
// Repeated for each level TRACE|DEBUG|INFO|WARN|ERROR|FATAL
}

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.

Logging Usage

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

...

2009-06-29 13:35:10,1234 +0100 [ con:1(guest, 127.0.0.1, /)/ch:2/sub:1:qu(myqueue) ] Subscription Event occcured.

pubic class Channel
...
    pluginbinding = getACLPlugin();new ExchangeBinding(...);
    ((LogEntity)binding).setCreator(connection);
... 
// Verify binding can be performed/created
...
    if (_statusLogger.isInfoEnabledForPlugin(plugin, thisisInfoEnabled(binding))
    {
        _statusLogger.pluginInfo(plugin, thisinfo(binding, "Plugin Event occured for this.Created");
    }
...

Would result in the following:

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

Initial Log Messages

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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