Log Output Adapter

The Log Output adapter itself adds negligible overhead to each tuple when the configured log level is such that no logging actually occurs. When the log level is such that tuples are actually sent into the logging system, the overhead can become significant, depending on the type of appenders configured. Even logging appenders that are said to be asynchronous can introduce surprising delays.

To avoid all overhead delays introduced by logging system appenders, select the Log Asynchronously check box. With this option enabled, each incoming tuple is sent immediately to the adapter's output port, and a copy of the tuple is sent to a queue. The queue is managed by a separate thread that immediately retrieves the tuple from the queue and sends it to the currently configured logging system. Because each tuple's retrieval from the queue is immediate, this option's actions do not constitute buffering, just separately-threaded logging. When you enable the Log Asynchronously option, the profiling Size attribute for the Log adapter reports the size of this queue.

There can be unintended consequences of enabling the Log Asynchronously option:

There is a Java system property, streambase.log-adapter-async, that can be used to set the synchronous state of all Log adapters in an application at the same time, without having to edit the Properties view for all Log adapters in the application. Set streambase.log-adapter-async=true to force all Log adapters to enable the Log Asynchronously option. Set the property =false to restore the default synchronous state of all Log adapters.

The Log adapter provides several ways to format the message portion of log entries emitted from the adapter.

The Logger Name property must be specified, and corresponds to the %c portion of the log message pattern string. Use different Logger names for Log adapters in different portions of your application.

By default, the Log adapter emits the fields of its input tuple preceded by the name of the Logger that you assign. For example, a Log adapter instance might be configured with the Logger1 Logger Name but no other formatting options. With the input tuple {IBM, 164.35, 1000}, the default-configured adapter emits the following message:

Logger1 - IBM,164.35,1000.0

You can optionally precede the emitted tuple with a string prefix that helps further identify log messages emitted from this instance of the adapter. For example:

Logger1 - Incoming tuple: IBM,164.35,1000.0

You can optionally precede each field value with its corresponding field name (with or without the message prefix). In this case, the listing of input fields is preceded by an internal counting field, tupleid. For example:

Logger1 - Incoming tuple: (tupleid=0,symbol="IBM",price=164.35,numshares=1000.0)

Lastly, instead of emitting the input tuple's fields in order, you can provide a string pattern in the format defined by java.text.MessageFormat, with zero-based positional parameters in the form {0}, {1}, and so on, filled in with input field values in input schema order. The message pattern option allows you to construct log message text in phrase or sentence form, with some or all of the log message text provided by the value of fields in the input tuple. For the same input tuple as above, with the message format string {2, number, integer} shares of {0} traded at {1, number, currency}., the adapter emits the following:

Logger1 - 1,000 shares of IBM traded at $164.35.

Name: Use this field to specify or change the component's name, which must be unique in the application. The name must contain only alphabetic characters, numbers, and underscores, and no hyphens or other special characters. The first character must be alphabetic or an underscore.

Adapter Name: A read-only field that shows the formal name of the adapter.

Class: A field that shows the fully qualified class name that implements the functionality of this adapter. Use this class name when loading the adapter in StreamSQL programs with the APPLY JAVA statement. You can right-click this field and select Copy from the context menu to place the full class name in the system clipboard.

Start with application: If this check box is selected, an instance of this adapter starts as part of the containing StreamBase Server. If cleared, the adapter is loaded with the server, but does not start until you send an sbadmin resume command, or start the component with StreamBase Manager. With this option cleared, the adapter does not start even if the application as a whole is suspended and later resumed. The default and recommended setting is selected.

Enable Error Output Port: Select this check box to add an Error Port to this component. In the EventFlow canvas, the Error Port shows as a red output port, always the last port for the component. See Using Error Ports and Error Streams to learn about Error Ports.

Description: Optionally enter text to briefly describe the component's purpose and function. In the EventFlow canvas, you can see the description by pressing Ctrl while the component's tooltip is displayed.

The Log adapter has the following properties on the Adapter Settings tab in its Properties View in StreamBase Studio:

{2, number, integer} shares of {0} traded at {1, number, currency}.

Use the Concurrency tab to specify separate threading for this instance of this component, or multiplicity options, or both. The Concurrency tab settings are described in Concurrency Options, and dispatch styles are described in Dispatch Styles.