HDFS XML File Writer Output Adapter

Introduction

The TIBCO StreamBase® XML File Writer for Apache Hadoop Distributed File System (HDFS) is an embedded adapter suitable for streaming tuples to a text file formatted with XML tags.

The XML file created by this adapter does not contain a root node. Each tuple streamed by the adapter should be treated as an individual document. Input fields of type list or tuple are not supported.

Each field value can be optionally parsed for XML reserved characters such as <, >, and & in field values and XML-escaped if detected. Parsing for XML escaping incurs a performance penalty; disable this feature (the default) if you are sure your input data contains no XML reserved characters.

The adapter rolls over its output file when it reaches the size specified in the (optional) Max File Size parameter. When an output file is rolled over, the current File Name is appended with the current date, formatted as: yyyyMMddhhmmss. If an output file was already created with a particular date suffix, then subsequent log files are further appended with the suffix -0, -1, -2, and so on.

The adapter flushes writes to disk after every tuple unless Flush Interval is specified. If Flush Interval is specified, then a flush() is done asynchronously. Each flush and write to the output file is synchronized to prevent partial tuples from being written to disk.

Properties

The HDFS XML File Writer adapter is configured with the properties shown in the following sections. In certain cases, properties can also be set in the StreamBase Server configuration file.

General Tab

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: 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 field is set to Yes or to a module parameter that evaluates to true, an instance of this adapter starts as part of the containing StreamBase Server. If this field is set to No or to a module parameter that evaluates to false, the adapter is loaded with the server, but does not start until you send an sbadmin resume command, or until you start the component with StreamBase Manager. With this option set to No or false, the adapter does not start even if the application as a whole is suspended and later resumed. The recommended setting is selected by default.

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.

Adapter Properties Tab

Property	Description	Default
File Name (string)	The local file path.	None
User (string)	The user to use for HDFS file access. An empty value means use the current system user.	None
Use Default Charset (optional bool)	Specifies whether the default Java platform character set should be used. If this check box is cleared, a valid character set name must be specified for the Character Set property.	cleared
Character Set (optional string)	The character set for the XML file you are writing. Note If you specify a non-ASCII character set such as UTF-8, remember that character mappings are not necessarily one byte to one byte in non-ASCII character sets.	The setting of the system property `streambase.tuple-charset`. `US-ASCII` if the property is not set.
Truncate File (bool)	If true, truncate log on startup.	false, append
Max File Size (optional int)	The maximum XML file size in bytes before roll; 0 = no roll.	0, unlimited
Buffer Size (optional int)	The buffer size, which must be greater than 0; 0 = no buffer.	0, unlimited
Flush Interval (optional int)	The frequency with which to force flush, in milliseconds; 0 = always flush.	0, write immediately
Escape (check box)	If selected, characters in input tuples such as <, >, and & are XML encoded with `< > &` respectively. If cleared, such characters are embedded in the resulting XML verbatim.	cleared
Log Level	Controls the level of verbosity the adapter uses to send notifications to the console. This setting can be higher than the containing application's log level. If set lower, the system log level will be used. Available values, in increasing order of verbosity, are: OFF, ERROR, WARN, INFO, DEBUG, TRACE, and ALL.	INFO

HDFS Tab

Property	Data Type	Description
Buffer Size (Bytes)	int	The size of the buffer to be used, if empty the default will be used
Replication	short	The required block replication for the file, if empty the server default will be used, only used during file creation
Block Size (Bytes)	long	The default data block size, if empty the server default will be used, only used during file creation

Concurrency Tab

Use the Concurrency tab to specify parallel regions 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.

Caution

Concurrency settings are not suitable for every application, and using these settings requires a thorough analysis of your application. For details, see Execution Order and Concurrency, which includes important guidelines for using the concurrency options.

XML Formatting

The XML file emitted from this adapter takes the following form for each input tuple:

<tuple>
    <FieldName1>FieldValue1</FieldName1>
    <FieldName2>FieldValue2</FieldName2>
    <FieldName3>FieldValue3</FieldName3>
    ...
</tuple>

Typechecking and Error Handling

Typechecking fails if the input tuple includes fields of type list or tuple, and if the following optional parameters are specified and do not meet the following conditions:

Max File Size must be greater than or equal to 0.
Flush Interval must be greater than or equal to 0.
Buffer Size must be greater than or equal to 0.

If specified and those conditions are not met, typechecking fails.

Suspend and Resume Behavior

On suspend, all tuples are written to disk and the currently open XML file is closed.

On resumption, caching is restarted. The first log message occurs at resume time + Flush Interval.