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through the synchronous SCA binding on each transaction, it is better to set modules A and B
to both use either eager parsing or lazy parsing.
The interaction between modules with different parsing modes takes place through
serialization and deserialization, which can negatively affect performance. If using a mixed
mode is unavoidable, starting an application from an eager parsing module to a lazy parsing
module is more efficient than the other way around. The output from the eager parsing
module is serialized into an XML string, and the target module using lazy parsing still benefits
fully from delayed parsing, producing this efficiency.
Share-by-reference libraries
Lazy parsing is optimized to use share-by-reference libraries. When a BO travels from one
module to another as a parameter of a synchronous SCA service invocation, a lazy copy is
used if the source and target modules share the BO schema through a share-by-reference
library. Without the share-by-reference optimization, the caller serializes the BO and the
callee deserializes the BO.
Differences in behavior for lazy parsing and eager parsing
If you are changing an application that was originally developed with eager parsing to use
lazy parsing, be aware of the differences in behavior between each mode, as summarized
here. Also consider the behavior differences between each node if you are planning to switch
an application between lazy and eager parsing mode.
Error handling
If the XML byte stream being parsed is ill-formed, parsing exceptions occur:
►
►
With eager parsing, the exceptions occur as soon as the BO is parsed from the inbound
XML stream.
With lazy parsing, the parsing exceptions occur latently when the application accesses the
BO properties and parses the portion of the XML that is ill-formed.
To properly handle ill-formed XML for either parsing mode, select one of the following options:
► Deploy a Mediation Flow Component on the application edges to validate inbound XML.
► Author lazy error-detection logic at the point where BO properties are accessed.
Exception stacks and messages
Because eager and lazy parsing have different underlying implementations, stack traces that
are generated by the BO programming interfaces and services have the same exception
class name. However, stack traces might not contain the same exception message or
wrapped set of implementation-specific exception classes.
XML serialization format
Lazy parsing provides a fast serialization optimization that attempts to copy unmodified XML
from the inbound data stream to the outbound data stream upon serialization. The fast
serialization improves performance, but the resultant serialization format of the outbound
XML data stream might be syntactically different than if the entire BO is updated in lazy
parsing, or if eager parsing is used.
The output XML serialization format might not be precisely syntactically equivalent across
these cases. However, the semantics of the XML data streams are equivalent, regardless of
the parsing mode, and the resultant XML can be safely passed between applications running
in different parsing modes with semantic equivalence.
Chapter 3. Development best practices 33