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Oracle® Streams Advanced Queuing User's Guide
11g Release 2 (11.2)

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20 Oracle Messaging Gateway Message Conversion

This chapter discusses how Oracle Messaging Gateway (MGW) converts message formats from one messaging system to another. A conversion is generally necessary when moving messages between Oracle Streams Advanced Queuing and another system, because different messaging systems have different message formats. Java Message Service (JMS) messages are a special case. A JMS message can be propagated only to a JMS destination, making conversion a simple process.

This chapter contains these topics:

Converting Oracle Messaging Gateway Non-JMS Messages

MGW converts the native message format of the source messaging system to the native message format of the destination messaging system during propagation. MGW uses canonical types and a model centering on Oracle Streams Advanced Queuing for the conversion.

Overview of the Non-JMS Message Conversion Process

When a message is propagated by MGW, the message is converted from the native format of the source queue to the native format of the destination queue.

A native message usually contains a message header and a message body. The header contains the fixed header fields that all messages in that messaging system have, such as message properties in Oracle Streams Advanced Queuing and the fixed header in WebSphere MQ. The body contains message contents, such as the Oracle Streams Advanced Queuing payload, the WebSphere MQ message body, or the entire TIB/Rendezvous message. MGW converts both message header and message body components.

Figure 20-1 shows how non-JMS messages are converted in two stages. A message is first converted from the native format of the source queue to the MGW internal message format, and then it is converted from the internal message format to the native format of the destination queue.

Figure 20-1 Non-JMS Message Conversion

Description of Figure 20-1 follows
Description of "Figure 20-1 Non-JMS Message Conversion"

The MGW agent uses an internal message format consisting of a header that is similar to the Oracle Streams Advanced Queuing message properties and a body that is a representation of an MGW canonical type.

Oracle Messaging Gateway Canonical Types

MGW defines canonical types to support message conversion between Oracle Streams Advanced Queuing and non-Oracle messaging systems. A canonical type is a message type representation in the form of a PL/SQL Oracle type in Oracle Database. The canonical types are RAW, SYS.MGW_BASIC_MSG_T, and SYS.MGW_TIBRV_MSG_T.

WebSphere MQ propagation supports the canonical types SYS.MGW_BASIC_MSG_T and RAW. TIB/Rendezvous propagation supports the canonical types SYS.MGW_TIBRV_MSG_T and RAW.

See Also:

"DBMS_MGWMSG" in Oracle Database PL/SQL Packages and Types Reference for Syntax and attribute information for SYS.MGW_BASIC_MSG_T and SYS.MGW_TIBRV_MSG_T

Message Header Conversion

MGW provides default mappings between Oracle Streams Advanced Queuing message properties and non-Oracle message header fields that have a counterpart in Oracle Streams Advanced Queuing message properties with the same semantics. Where MGW does not provide a mapping, the message header fields are set to a default value, usually the default value defined by the messaging system.

Handling Arbitrary Payload Types Using Message Transformations

When converting to or from Oracle Streams Advanced Queuing messages, the MGW agent uses only its canonical types. Arbitrary payload types are supported, however, with the assistance of user-defined Oracle Streams Advanced Queuing message transformations to convert between an Oracle Streams Advanced Queuing queue payload and an MGW canonical type.

For MGW to propagate messages from an Oracle Streams Advanced Queuing queue with an arbitrary ADT payload (outbound propagation), you must provide a mapping to an MGW canonical ADT. The transformation is invoked when the MGW agent dequeues messages from the Oracle Streams Advanced Queuing queue. Similarly, for MGW to propagate messages to an Oracle Streams Advanced Queuing queue with an arbitrary ADT payload (inbound propagation), you must provide a mapping from an MGW canonical ADT. The transformation is invoked when the MGW agent enqueues messages to the Oracle Streams Advanced Queuing queue.

Figure 20-2 Oracle Streams Advanced Queuing Message Conversion

Description of Figure 20-2 follows
Description of "Figure 20-2 Oracle Streams Advanced Queuing Message Conversion"

The transformation is always executed in the context of the MGW agent, which means that the MGW agent user (the user specified using DBMS_MGWADM.CREATE_AGENT or DBMS_MGWADM.ALTER_AGENT) must have EXECUTE privileges on the transformation function and the Oracle Streams Advanced Queuing payload type. This can be accomplished by granting the EXECUTE privilege to PUBLIC or by granting the EXECUTE privilege directly to the MGW agent user.

To configure a MGW propagation job with a transformation:

  1. Create the transformation function.

  2. Grant EXECUTE to the MGW agent user or to PUBLIC on the function and the object types it references.

  3. Call DBMS_TRANSFORM.CREATE_TRANSFORMATION to register the transformation.

  4. Call DBMS_MGWADM.CREATE_JOB to create a MGW propagation job using the transformation, or DBMS_MGWADM.ALTER_JOB to alter an existing job.

The value passed in the transformation parameter for these APIs must be the registered transformation name and not the function name. For example, trans_sampleadt_to_mgw_basic is a stored procedure representing a transformation function with the signature shown in Example 20-1.

Note:

All commands in the examples must be run as a user granted MGW_ADMINISTRATOR_ROLE, except for the commands to create transformations.

Example 20-1 Transformation Function Signature

FUNCTION trans_sampleadt_to_mgw_basic(in_msg IN mgwuser.sampleADT)
RETURN SYS.MGW_BASIC_MSG_T;

You can create a transformation using DBMS_TRANSFORM.CREATE_TRANSFORMATION, as shown in Example 20-2.

Example 20-2 Creating a Transformation

BEGIN
  DBMS_TRANSFORM.CREATE_TRANSFORMATION(
        schema         => 'mgwuser',
        name           => 'sample_adt_to_mgw_basic',
        from_schema    => 'mgwuser',
        from_type      => 'sampleadt',
        to_schema      => 'sys',
        to_type        => 'MGW_BASIC_MSG_T',
        transformation => 'mgwuser.trans_sampleadt_to_mgw_basic(user_data)');
END;

Once created, this transformation can be registered with MGW when creating a propagation job. Example 20-3 creates job job_aq2mq, for whom messages are propagated from Oracle Streams Advanced Queuing queue mgwuser.srcq to non-Oracle messaging system queue destq@mqlink using transformation mgwuser.sample_adt_to_mgw_basic.

Example 20-3 Registering a Transformation

BEGIN
  DBMS_MGWADM.CREATE_JOB(
    job_name          =>   'job_aq2mq',
    propagation_type  =>    DBMS_MGWADM.OUTBOUND_PROPAGATION,
    source            =>   'mgwuser.srcq',
    destination       =>   'destq.mqlink',
    transformation    =>   'mgwuser.sample_adt_to_mgw_basic',
    exception_queue   =>   'mgwuser.excq');
END;

See Also:

"DBMS_MGWADM", "DBMS_MGWMSG", and "DBMS_TRANSFORM" in Oracle Database PL/SQL Packages and Types Reference

An error that occurs while attempting a user-defined transformation is usually considered a message conversion exception, and the message is moved to the exception queue if it exists.

Handling Logical Change Records

MGW provides facilities to propagate Logical Change Records (LCRs). Routines are provided to help in creating transformations to handle the propagation of both row LCRs and DDL LCRs stored in queues with payload type ANYDATA. An LCR is propagated as an XML string stored in the appropriate message type.

Note:

For LCR propagation, you must load the XDB package.

Because Oracle Streams uses ANYDATA queues to store LCRs, an ANYDATA queue is the source for outbound propagation. The transformation must first convert the ANYDATA object containing an LCR into an XMLType object using the MGW routine DBMS_MGWMSG.LCR_TO_XML. If the ANYDATA object does not contain an LCR, then this routine raises an error. The XML document string of the LCR is then extracted from the XMLType and placed in the appropriate MGW canonical type (SYS.MGW_BASIC_MSG_T or SYS.MGW_TIBRV_MSG_T).

Example 20-4 illustrates a simplified transformation used for LCR outbound propagation. The transformation converts an ANYDATA payload containing an LCR to a SYS.MGW_TIBRV_MSG_T object. The string representing the LCR as an XML document is put in a field named ORACLE_LCR.

Example 20-4 Outbound LCR Transformation

create or replace function any2tibrv(adata in anydata)
return SYS.MGW_TIBRV_MSG_T is
    v_xml   XMLType;
    v_text  varchar2(2000);
    v_tibrv sys.mgw_tibrv_msg_t;
BEGIN
    v_xml   := dbms_mgwmsg.lcr_to_xml(adata);
    -- assume the lcr is smaller than 2000 characters long.
    v_text  := v_xml.getStringVal();
    v_tibrv := SYS.MGW_TIBRV_MSG_T.CONSTRUCT;
    v_tibrv.add_string('ORACLE_LCR', 0, v_text);
    return v_tibrv;
END any2tibrv;

For LCR inbound propagation, an MGW canonical type (SYS.MGW_BASIC_MSG_T or SYS.MGW_TIBRV_MSG_T) is the transformation source type. A string in the format of an XML document representing an LCR must be contained in the canonical type. The transformation function must extract the string from the message, create an XMLType object from it, and convert it to an ANYDATA object containing an LCR with the MGW routine DBMS_MGWMSG.XML_TO_LCR. If the original XML document does not represent an LCR, then this routine raises an error.

Example 20-5 illustrates a simplified transformation used for LCR inbound propagation. The transformation converts a SYS.MGW_TIBRV_MSG_T object with a field containing an XML string representing an LCR to an ANYDATA object. The string representing the LCR as an XML document is taken from a field named ORACLE_LCR.

Example 20-5 Inbound LCR Transformation

create or replace function tibrv2any(tdata in sys.mgw_tibrv_msg_t)
return anydata is 
    v_field   sys.mgw_tibrv_field_t;
    v_xml     XMLType;
    v_text    varchar2(2000);
    v_any     anydata;
BEGIN
    v_field := tdata.get_field_by_name('ORACLE_LCR');
    -- type checking
    v_text  := v_field.text_value;
    -- assume it is not null
    v_xml  := XMLType.createXML(v_text);
    v_any  := dbms_mgwmsg.xml_to_lcr(v_xml); 
    return v_any;
END tibrv2any;

See Also:

Message Conversion for WebSphere MQ

MGW converts between the MGW canonical types and the WebSphere MQ native message format. WebSphere MQ native messages consist of a fixed message header and a message body. The message body is treated as either a TEXT value or RAW (bytes) value. The canonical types supported for WebSphere MQ propagation are SYS.MGW_BASIC_MSG_T and RAW.

Figure 20-3 Message Conversion for WebSphere MQ Using MGW_BASIC_MSG_T

Description of Figure 20-3 follows
Description of "Figure 20-3 Message Conversion for WebSphere MQ Using MGW_BASIC_MSG_T"

Figure 20-3 illustrates the message conversion performed by the MGW WebSphere MQ driver when using the canonical type SYS.MGW_BASIC_MSG_T. For outbound propagation, the driver maps the Oracle Streams Advanced Queuing message properties and canonical message to a WebSphere MQ message having a fixed header and a message body. For inbound propagation, the driver maps a native message to a set of Oracle Streams Advanced Queuing message properties and a canonical message. When the canonical type is RAW, the mappings are the same, except no canonical headers exist.

WebSphere MQ Message Header Mappings

When the MGW canonical type used in an outbound propagation job is RAW, no WebSphere MQ header information is set from the RAW message body. Similarly, for inbound propagation no WebSphere MQ header information is preserved in the RAW message body. MGW canonical type SYS.MGW_BASIC_MSG_T, however, has a header that can be used to specify WebSphere MQ header fields for outbound propagation, and preserve WebSphere MQ header fields for inbound propagation.

This section describes the message properties supported for the WebSphere MQ messaging system when using SYS.MGW_BASIC_MSG_T as the canonical type. Table 20-1 defines the MGW {name, value} pairs used to describe the WebSphere MQ header properties. The first column refers to valid string values for the SYS.MGW_NAME_VALUE_T.NAME field in the SYS.MGW_BASIC_MSG_T header. The second column refers to the SYS.MGW_NAME_VALUE_T.TYPE value corresponding to the name. (Refer to "Notes on Table 20-1" for explanations of the numbers in parentheses.)

For inbound propagation, the WebSphere MQ driver generates {name,value} pairs based on the source message header and stores them in the header part of the canonical message of the SYS.MGW_BASIC_MSG_T type. For outbound propagation, the WebSphere MQ driver sets the message header and enqueue options from {name,value} pairs for these properties stored in the header part of the SYS.MGW_BASIC_MSG_T canonical message.

Table 20-1 MGW Names for WebSphere MQ Header Values

MGW Name MGW Type WebSphere MQ Property Name Used For
MGW_MQ_accountingToken
RAW_VALUE (size 32)
accountingToken

Outbound (1), Inbound

MGW_MQ_applicationIdData
TEXT_VALUE (size 32)
applicationIdData 

Outbound (1), Inbound

MGW_MQ_applicationOriginData
TEXT_VALUE (size 4)
applicationOriginData

Outbound (1), Inbound

MGW_MQ_backoutCount
INTEGER_VALUE
backoutCount

Inbound

MGW_MQ_characterSet
INTEGER_VALUE
characterSet

Outbound, Inbound

MGW_MQ_correlationId
RAW_VALUE (size 24)
correlationId

Outbound (1), Inbound

MGW_MQ_encoding
INTEGER_VALUE
encoding

Outbound, Inbound

MGW_MQ_expiry
INTEGER_VALUE
expiry

Outbound, Inbound

MGW_MQ_feedback
INTEGER_VALUE
feedback

Outbound, Inbound

MGW_MQ_format
TEXT_VALUE (size 8)
format

Outbound (1), Inbound

MGW_MQ_groupId
RAW_VALUE (size 24)
groupId

Outbound (1), Inbound

MGW_MQ_messageFlags
INTEGER_VALUE
messageFlags

Outbound, Inbound

MGW_MQ_messageId
RAW_VALUE (size 24)
messageId

Outbound, Inbound

MGW_MQ_messageSequenceNumber
INTEGER_VALUE
messageSequenceNumber

Outbound, Inbound

MGW_MQ_messageType
INTEGER_VALUE
messageType

Outbound, Inbound

MGW_MQ_offset
INTEGER_VALUE
offset

Outbound, Inbound

MGW_MQ_originalLength
INTEGER_VALUE
originalLength

Outbound, Inbound

MGW_MQ_persistence
INTEGER_VALUE
persistence

Inbound

MGW_MQ_priority
INTEGER_VALUE
priority

Outbound, Inbound

MGW_MQ_putApplicationName
TEXT_VALUE (size 28)
putApplicationName

Outbound (1), Inbound

MGW_MQ_putApplicationType
INTEGER_VALUE
putApplicationType

Outbound (1), Inbound

MGW_MQ_putDateTime
DATE_VALUE
putDateTime

Inbound

MGW_MQ_putMessageOptions
INTEGER_VALUE
putMessageOptions

Outbound (1) (2)

MGW_MQ_replyToQueueManagerName
TEXT_VALUE (size 48)
replyToQueueManagerName

Outbound, Inbound

MGW_MQ_replyToQueueName
TEXT_VALUE (size 48)
replyToQueueName

Outbound, Inbound

MGW_MQ_report
INTEGER_VALUE
report

Outbound (1), Inbound

MGW_MQ_userId
TEXT_VALUE (size 12)
userId

Outbound, Inbound


Notes on Table 20-1

  1. This use is subject to WebSphere MQ restrictions. For example, if MGW_MQ_accountingToken is set for an outgoing message, then WebSphere MQ overrides its value unless MGW_MQ_putMessageOptions is set to the WebSphere MQ constant MQPMD_SET_ALL_CONTEXT.

  2. MGW_MQ_putMessageOptions is used as the putMessageOptions argument to the WebSphere MQ Base Java Queue.put() method. It is not part of the WebSphere MQ header information and is therefore not an actual message property.

    The value for the openOptions argument of the WebSphere MQ Base Java MQQueueManager.accessQueue method is specified when the WebSphere MQ queue is registered using the DBMS_MGWADM.REGISTER_FOREIGN_QUEUE call. Dependencies can exist between the two. For instance, for MGW_MQ_putMessageOptions to include MQPMD_SET_ALL_CONTEXT, the MQ_openMessageOptions queue option must include MQOO_SET_CONTEXT.

    The MGW agent adds the value MQPMO_SYNCPOINT to any value that you can specify.

MGW sets default values for two WebSphere MQ message header fields: messageType defaults to MQMT_DATAGRAM and putMessageOptions defaults to MQPMO_SYNCPOINT.

MGW provides two default mappings between Oracle Streams Advanced Queuing message properties and WebSphere MQ header fields.

One maps the Oracle Streams Advanced Queuing message property expiration, representing the time-to-live of the message at the time the message becomes available in the queue, to the WebSphere MQ header field expiry, representing the time-to-live of the message. For outbound propagation, the value used for expiry is determined by subtracting the time the message was available in the queue from the expiration, converted to tenths of a second. Oracle Streams Advanced Queuing value NEVER is mapped to MQEI_UNLIMITED. For inbound propagation, the value of expiration is simply expiry converted to seconds. WebSphere MQ value MQEI_UNLIMITED is mapped to NEVER.

The other default maps Oracle Streams Advanced Queuing message property priority with the WebSphere MQ header field priority. It is described in Table 20-2.

Table 20-2 Default Priority Mappings for Propagation

Propagation Type Message System Priority Values

Outbound

Oracle Streams Advanced Queuing

0

1

2

3

4

5

6

7

8

9

Outbound

WebSphere MQ

9

8

7

6

5

4

3

2

1

0

Inbound

Oracle Streams Advanced Queuing

9

8

7

6

5

4

3

2

1

0

Inbound

WebSphere MQ

0

1

2

3

4

5

6

7

8

9


Note:

For outbound propagation, Oracle Streams Advanced Queuing priority values less than 0 are mapped to WebSphere MQ priority 9, and Oracle Streams Advanced Queuing priority values greater than 9 are mapped to WebSphere MQ priority 0.

WebSphere MQ Outbound Propagation

If no message transformation is provided for outbound propagation, then the Oracle Streams Advanced Queuing source queue payload type must be either SYS.MGW_BASIC_MSG_T or RAW. If a message transformation is specified, then the target ADT of the transformation must be SYS.MGW_BASIC_MSG_T, but the source ADT can be any ADT supported by Oracle Streams Advanced Queuing.

If the Oracle Streams Advanced Queuing queue payload is RAW, then the resulting WebSphere MQ message has the message body set to the value of the RAW bytes and, by default, the format field set to the value "MGW_Byte".

If the Oracle Streams Advanced Queuing queue payload or transformation target ADT is SYS.MGW_BASIC_MSG_T, then the message is mapped to a WebSphere MQ native message as follows:

  • The WebSphere MQ fixed header fields are based on the internal Oracle Streams Advanced Queuing message properties and the SYS.MGW_BASIC_MSG_T.header attribute of the canonical message, as described in "WebSphere MQ Message Header Mappings".

  • If the canonical message has a TEXT body, then the WebSphere MQ format header field is set to MQFMT_STRING unless overridden by the header property MGW_MQ_format. The message body is treated as text.

  • If the canonical message has a RAW body, then the WebSphere MQ format header field is set to "MGW_Byte" unless overridden by the header property MGW_MQ_format. The message body is treated as raw bytes.

  • If the canonical message has both a TEXT and RAW body, then message conversion fails.

  • If the canonical message has neither a TEXT nor RAW body, then no message body is set, and the WebSphere MQ format header field is MQFMT_NONE.

  • If the canonical message has a TEXT body with both small and large values set (SYS.MGW_BASIC_MSG_T.TEXT_BODY.small_value and SYS.MGW_BASIC_MSG_T.TEXT_BODY.large_value not empty), then message conversion fails.

  • If the canonical message has a RAW body with both small and large values set (SYS.MGW_BASIC_MSG_T.RAW_BODY.small_value and SYS.MGW_BASIC_MSG_T.RAW_BODY.large_value not empty), then message conversion fails.

If the job option PreserveMessageID is specified with a value of TRUE, then the correlationId field of the WebSphere message header will be set to the AQ source message identifier. The correlationId value will be a 24-byte value of the form "AQMSGID:"+AQ_msgid where AQ_msgid represents the 16-byte Streams AQ message identifier.

WebSphere MQ Inbound Propagation

If no message transformation is provided for inbound propagation, then the Oracle Streams Advanced Queuing destination queue payload type must be either SYS.MGW_BASIC_MSG_T or RAW. If a message transformation is specified, then the source ADT of the transformation must be SYS.MGW_BASIC_MSG_T, but the destination ADT can be any ADT supported by Oracle Streams Advanced Queuing.

If the Oracle Streams Advanced Queuing queue payload is RAW and the incoming WebSphere MQ message has a format of MQFMT_STRING, then message conversion fails. Otherwise the message body is considered as raw bytes and enqueued directly to the destination queue. If the number of bytes is greater than 32KB, then message conversion fails. The actual limit is 32512 bytes rather than 32767 bytes.

If the Oracle Streams Advanced Queuing queue payload or transformation source ADT is SYS.MGW_BASIC_MSG_T, then the WebSphere MQ message is mapped to a SYS.MGW_BASIC_MSG_T message as follows:

  • Specific WebSphere MQ header fields are mapped to Oracle Streams Advanced Queuing message properties as previously described.

  • The SYS.MGW_BASIC_MSG_T.header attribute of the canonical message is set to {name, value} pairs based on the WebSphere MQ header fields, as described in Table 20-1. These values preserve the original content of the WebSphere MQ message header.

  • If the WebSphere MQ format header field is MQFMT_STRING, then the WebSphere MQ message body is treated as text, and its value is mapped to SYS.MGW_BASIC_MSG_T.text_body. For any other format value, the message body is treated as raw bytes, and its value is mapped to SYS.MGW_BASIC_MSG_T.raw_body.

Message Conversion for TIB/Rendezvous

MGW regards a TIB/Rendezvous message as a set of fields and supplementary information. Figure 20-4 shows how messages are converted between MGW and TIB/Rendezvous.

Figure 20-4 Message Conversion for TIB/Rendezvous

Description of Figure 20-4 follows
Description of "Figure 20-4 Message Conversion for TIB/Rendezvous"

When a message conversion failure occurs, messages are moved to an exception queue (if one has been provided), so that MGW can continue propagation of the remaining messages in the source queue. In inbound propagation from TIB/Rendezvous, an exception queue is a registered subject.

All TIB/Rendezvous wire format datatypes for TIB/Rendezvous fields are supported, except for the datatypes with unsigned integers and the nested message type. User-defined custom datatypes are not supported in this release. If a message contains data of the unsupported datatypes, then a message conversion failure occurs when the message is processed. A message conversion failure results in moving the failed message from the source queue to the exception queue, if an exception queue is provided.

Table 20-3 shows the datatype mapping used when MGW converts between a native TIB/Rendezvous message and the canonical ADT. For each supported TIB/Rendezvous wire format type, it shows the Oracle type used to store the data and the DBMS_MGWMSG constant that represents that type.

Table 20-3 TIB/Rendezvous Datatype Mapping

TIB/Rendezvous Wire Format Oracle Type ADT Field Type

Bool

NUMBER

TIBRVMSG_BOOL

F32

NUMBER

TIBRVMSG_F32

F64

NUMBER

TIBRVMSG_F64

I8

NUMBER

TIBRVMSG_I8

I16

NUMBER

TIBRVMSG_I16

I32

NUMBER

TIBRVMSG_I32

I64

NUMBER

TIBRVMSG_I64

U8

not supported

not supported

U16

not supported

not supported

U32

not supported

not supported

U64

not supported

not supported

IPADDR32

VARCHAR2

TIBRVMSG_IPADDR32

IPPORT16

NUMBER

TIBRVMSG_IPPORT16

DATETIME

DATE

TIBRVMSG_DATETIME

F32ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_F32ARRAY

F64ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_F64ARRAY

I8ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_I8ARRAY

I16ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_I16ARRAY

I32ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_I32ARRAY

I64ARRAY

SYS.MGW_NUMBER_ARRAY_T

TIBRVMSG_I64ARRAY

U8ARRAY

not supported

not supported

U16ARRAY

not supported

not supported

U32ARRAY

not supported

not supported

U64ARRAY

not supported

not supported

MSG

not supported

not supported

OPAQUE

RAW or BLOB

TIBRVMSG_OPAQUE

STRING

VARCHAR2 or CLOB

TIBRVMSG_STRING

XML

RAW or BLOB

TIBRVMSG_XML


For propagation between Oracle Streams Advanced Queuing and TIB/Rendezvous, MGW provides direct support for the Oracle Streams Advanced Queuing payload types RAW and SYS.MGW_TIBRV_MSG_T. To support any other Oracle Streams Advanced Queuing payload type, you must supply a transformation.

AQ Message Property Mapping for TIB/Rendezvous

This section describes the mapping between Oracle Streams AQ message properties and TIB/Rendezvous fields. This mapping is used to preserve Streams AQ message properties during outbound propagation, and set Streams AQ message properties during inbound propagation.

Table 20-4 describes the Streams AQ message properties supported using TIB/Rendezvous fields. The first column indicates the DBMS_AQ.MESSAGE_PROPERTIES_T field for the Streams AQ message property. The second and third columns indicate the name and datatype used for the TIB/Rendezvous field. The last column indicates if the message property is supported for inbound and outbound propagation.

Table 20-4 TIB/Rendezvous and MGW Names for Oracle Streams Advanced Queuing Message Properties

Oracle Streams Advanced Queuing Message Property MGW Name TIB/Rendezvous Wire Format Datatype Used For

priority

MGW_AQ_priority

TibrvMsg.I32

Outbound, Inbound

expiration

MGW_AQ_expiration

TibrvMsg.I32

Outbound, Inbound

delay

MGW_AQ_delay

TibrvMsg.I32

Outbound, Inbound

correlation

MGW_AQ_correlation

TibrvMsg.STRING

Outbound, Inbound

exception_queue

MGW_AQ_exception_queue

TibrvMsg.STRING

Outbound, Inbound

enqueue_time

MGW_AQ_enqueue_time

TibrvMsg.DATETIME

Outbound

original_msgid

MGW_AQ_original_msgid

TibrvMsg.OPAQUE

Outbound

msgid (1)

MGW_AQ_messageID

TibrvMsg.OPAQUE

Outbound


Notes on Table 20-4:

  1. The msgid Streams AQ property represents the Streams AQ message identifier, rather than a particular field of the DBMS_AQ.MESSAGE_PROPERTIES_T record.

TIB/Rendezvous Outbound Propagation

If no propagation transformation is provided for outbound propagation, then the Oracle Streams Advanced Queuing source queue payload type must be either SYS.MGW_TIBRV_MSG_T or RAW. If a propagation transformation is specified, then the target ADT of the transformation must be SYS.MGW_TIBRV_MSG_T, but the source ADT can be any ADT supported by Oracle Streams Advanced Queuing.

If the Oracle Streams Advanced Queuing queue payload or transformation target ADT is SYS.MGW_TIBRV_MSG_T, then:

  • Every field in the source message is converted to a TIB/Rendezvous message field of the resulting TIB/Rendezvous message.

  • If the reply_subject attribute is not NULL, then the reply subject supplementary information is set.

  • The send_subject field is ignored.

If the Oracle Streams Advanced Queuing queue payload is RAW, then:

  • The resulting message contains a field named MGW_RAW_MSG with value TibrvMsg.OPAQUE. The field ID is set to 0.

If the job option AQ_MsgProperties is specified with a value of TRUE, then the MGW agent generates fields to preserve the Streams AQ message properties in the TIB/Rendezvous message according to Table 20-4.

If the PreserveMessageID job option is specified with a value of TRUE, then the Streams AQ message identifier (msgid) is preserved in the TIB/Rendezvous message according to Table 20-4.

TIB/Rendezvous Inbound Propagation

If no propagation transformation is provided for inbound propagation, then the Oracle Streams Advanced Queuing destination queue payload type must be either RAW or SYS.MGW_TIBRV_MSG_T. If a propagation transformation is specified, then the target ADT of the transformation can be any ADT supported by Oracle Streams Advanced Queuing, but the source ADT of the transformation must be SYS.MGW_TIBRV_MSG_T.

If the Oracle Streams Advanced Queuing queue payload or transformation source ADT is SYS.MGW_TIBRV_MSG_T, then:

  • Every field in the source TIB/Rendezvous message is converted to a field of the resulting message of the SYS.MGW_TIBRV_MSG_T type.

  • The MGW agent extracts the send subject name from the source TIB/Rendezvous message and sets the send_subject attribute in SYS.MGW_TIBRV_MSG_T. The send subject name is usually the same as the subject name of the registered propagation source queue, but it might be different when wildcards are used.

  • The MGW agent extracts the reply subject name from the source TIB/Rendezvous message, if it exists, and sets the reply_subject attribute in SYS.MGW_TIBRV_MSG_T.

  • If the source TIB/Rendezvous message contains more than three large text fields (greater than 4000 bytes of text) or more than three large bytes fields (greater than 2000 bytes), then message conversion fails.

If the Oracle Streams Advanced Queuing queue payload is RAW, then:

  • The Oracle Streams Advanced Queuing message payload is the field data if the source TIB/Rendezvous message has a field named MGW_RAW_MSG of type TibrvMsg.OPAQUE or TibrvMsg.XML. The field name and ID are ignored. If no such field exists or has an unexpected type, then a message conversion failure occurs.

  • A message conversion failure occurs if the RAW data size is greater than 32KB. This is due to a restriction on the data size allowed for a bind variable. Also, the actual limit is 32512 rather than 32767.

If the job option AQ_MsgProperties is specified with a value of TRUE, then the MGW agent searches for fields in the original TIB/Rendezvous messages with reserved field names. Table 20-4 shows the field name strings and the corresponding values used in the TIB/Rendezvous message.

If such fields exist, then the MGW agent uses the field value to set the corresponding Oracle Streams Advanced Queuing message properties, instead of using the default values. If there is more than one such field with the same name, then only the first one is used. Such fields are removed from the resulting payload only if the Oracle Streams Advanced Queuing queue payload is RAW. If a field with the reserved name does not have the expected datatype, then it causes a message conversion failure.

See Also:

"DBMS_MGWMSG" in Oracle Database PL/SQL Packages and Types Reference for the value datatypes

JMS Messages

MGW propagates only JMS messages between Oracle JMS and non-Oracle JMS systems, without changing the message content. Figure 20-5 shows JMS message propagation.

MGW supports only the standard JMS message types. It does not support:

  • JMS provider extensions, because any such extensions would not be recognized by the destination JMS system. An attempt to propagate any such non-JMS message results in an error.

  • User transformations for JMS propagation.

  • Propagation of Logical Change Records (LCRs).

Figure 20-5 JMS Message Propagation

Description of Figure 20-5 follows
Description of "Figure 20-5 JMS Message Propagation"

For the purposes of this discussion, a JMS message is a Java object of a class that implements one of the five JMS message interfaces. Table 20-5 shows the JMS message interfaces and the corresponding Oracle JMS ADTs. The table also shows the interface, javax.jms.Message, which can be any one of the five specific types, and the corresponding generic Oracle JMS type SYS.AQ$_JMS_MESSAGE.

Table 20-5 Oracle JMS Message Conversion

JMS Message ADT

javax.jms.TextMessage

SYS.AQ$_JMS_TEXT_MESSAGE

javax.jms.BytesMessage

SYS.AQ$_JMS_BYTES_MESSAGE

javax.jms.MapMessage

SYS.AQ$_JMS_MAP_MESSAGE

javax.jms.StreamMessage

SYS.AQ$_JMS_STREAM_MESSAGE

javax.jms.ObjectMessage

SYS.AQ$_JMS_OBJECT_MESSAGE

javax.jms.Message

SYS.AQ$_JMS_MESSAGE


When a propagation job is activated, the MGW agent checks the Oracle Streams Advanced Queuing payload type for the propagation source or destination. If the type is one of those listed in Table 20-5 or ANYDATA, then message propagation is attempted. Otherwise an exception is logged and propagation is not attempted.

The MGW agent may add a JMS String property named OracleMGW_OriginalMessageID to the JMS message sent to the destination queue in order to preserve the original message identifier of the source message. This property is added if the PreserveMessageID job option is specified with a value of TRUE. It will also be added for any message moved to an exception queue upon a message conversion failure.

JMS Outbound Propagation

When dequeuing a message from an Oracle Streams Advanced Queuing queue, Oracle JMS converts instances of the ADTs shown in Table 20-5 into JMS messages. In addition it can convert instances of ANYDATA into JMS messages, depending on the content.

A queue with payload type ANYDATA can hold messages that do not map to a JMS message. MGW fails to dequeue such a message. An error is logged and propagation of messages from that queue does not continue until the message is removed.

JMS Inbound Propagation

Every message successfully dequeued using WebSphere MQ JMS is a JMS message. No message conversion is necessary prior to enqueuing using Oracle JMS. However, if the payload ADT of the propagation destination does not accept the type of the inbound message, then an exception is logged and an attempt is made to place the message in an exception queue. An example of such type mismatches is a JMS TextMessage and a queue payload type SYS.AQ$_JMS_BYTES_MESSAGE.